Weight loss peptides: claims, scientific evidence and limitations

Peptides often appear in studies on weight loss and in online discussions about weight loss. This is due, among other things, to the fact that some drugs with peptide structure affect the signaling systems related to appetite, satiety, glucose regulation, the physiology of the gastrointestinal tract, and other metabolic processes.

Large randomized clinical trials have shown significant weight reduction with specific interventions, including semaglutide and tirzepatide. These results are clinically significant, but they do not mean that all peptides cause weight loss, that every substance labeled as a „weight loss peptide” has comparable evidence, or that an unstudied product can replicate the results of a regulated drug. [1] [2]

The most important thing is to distinguish between chemical category a clinically researched treatment.

The term „weight loss peptides” can refer to very different products and substances, such as:

• approved prescription medications;
• experimental compounds that are in the phase of clinical trials;
• prescription drugs;
• supplements;
• products sold as research materials;
• substances grouped together in commercial offers despite different pharmacological properties.

They cannot be treated as equivalent in terms of evidence, formulation, production control, regulatory status, or clinical significance.

The strongest evidence in this field concerns specific products. It comes from studies of specific interventions conducted in defined populations, using specific formulations, comparators, endpoints, treatment periods, and statistical analysis methods.

In the article we explain what the most important results of body mass measurements really mean, what we learned from groundbreaking clinical studies, how body weight change differs from body composition change, why maintaining the effect after the end of treatment is a separate research question, and how to interpret data on cardiovascular health, safety, and regulatory status.

A broader discussion of why evidence regarding different peptide interventions should be analyzed separately can also be found in the article: Peptide therapy: what does this term mean and why do the scientific evidence differ so much?.

This text is an educational review of scientific evidence. It is not a guide for choosing a treatment, prescribing medications, dosing, preparing, or administering peptides.

The regulatory examples relate to specific jurisdictions, and their status was reviewed on September 20, 2026.

Why do peptides appear in searches related to weight loss?

Appetite signaling is one reason, but not a universal property of peptides

Some naturally occurring peptide hormones participate in communication between the gastrointestinal tract, the pancreas, the brain, and other tissues involved in energy regulation.

The development of drugs can exploit these biological pathways by creating molecules with properties suitable for specific clinical applications.

Semaglutide works on GLP-1 receptor, However, tirzepatide acts on GIP and GLP-1 receptors. Clinical data relate specifically to these specific substances, formulations, populations, and treatment programs.[1][2]

This distinction is crucial.

A peptide that acts on a completely different receptor does not accept evidence regarding weight control associated with semaglutide or tirzepatide simply because it also consists of amino acid residues.

Even similar relationships are not automatically equivalent

Substances acting within similar signaling systems may differ in terms of:

• receptor activity;
• selectivity towards receptors;
• pharmacokinetics;
• exposure time;
• modifications of the molecule;
• formulation;
• tolerance;
• adverse effects;
• clinical results.

The similarity of the mechanism may justify further research.

However, it does not guarantee comparable weight reduction.

Does „GLP-1” mean that all products have the same evidence?

No.

Terms related to GLP-1 describe a biological pathway or pharmacological target, not a single interchangeable product.

Individual drugs may differ in molecular structure, receptor activity, exposure, formulation, approved indications, and clinical results.

Therefore, evidence regarding semaglutide cannot be automatically transferred to another product related to GLP-1 or another peptide substance without appropriate studies. [1]

„Peptide” does not automatically mean „weight loss peptide”

Peptides perform many functions in biology that are not related to weight regulation.

They can participate in, among others:

• cellular signaling;
• regulation of the immune system;
• communication between tissues;
• hormonal physiology;
• neurological processes;
• the functioning of the digestive tract;
• many other biological processes.

The fact that some peptide drugs affect body weight does not mean that weight loss is a general property of peptides.

Weight loss, appetite and metabolism are different outcomes

The study may show a change in appetite without proving a sustained reduction in body weight.

It can also show a change in glucose levels or other metabolic biomarkers without measuring fat tissue.

Perhaps it can finally show an initial reduction in body weight without answering the question of whether the effect will persist after the end of the treatment.

These results should not be equated with one another.

Appetite is a separate endpoint

The study can measure:

• feeling of hunger;
• satiety;
• the amount of food consumed;
• food preferences;
• other variables related to appetite.

Such results can help to understand the mechanism of action.

However, they are not automatically evidence of a long-term reduction in body weight.

Does a reduction in appetite indicate a sustained loss of weight?

No.

Appetite is one result, whereas sustained weight loss requires direct measurement of body weight over a sufficiently long period of time.

The short-term effect on appetite does not automatically determine the magnitude or durability of subsequent changes in body weight.

Large clinical studies measured body weight over many months, instead of inferring changes in it based solely on mechanisms related to appetite. [1] [2]

Metabolic changes should also be analyzed separately

Changes regarding:

• glucose;
• Insulins;
• lipids;
• energy expenditure;
• other metabolic markers

They may be scientifically significant without confirmation of a specific reduction in body mass or fat tissue.

Does weight loss automatically mean an improvement in metabolic health?

Not every metabolic outcome can be inferred solely from a change in the weight indication.

The studies can separately analyze:

• glucose;
• insulin;
• arterial pressure;
• lipids;
• other metabolic parameters.

If an article states an improvement in a specific parameter, it should be based on a study that actually measured it.

Broad marketing definitions can blur the differences

In search results, terms such as:

• „fat-burning peptide”;
• „peptide for metabolism”;
• „an appetite-suppressing peptide”;
• „a peptide for weight loss”;
• „a peptide for reshaping the figure”.

Such terms can give the impression that different results are interchangeable.

A better question is:

What exactly was measured in the study?

If body mass was measured, the body mass should be reported.

If adipose tissue was examined, adipose tissue should be reported.

If appetite is being assessed, it should be referred to as appetite.

If a metabolic biomarker was measured, that biomarker should be specified.

Animal studies require careful transfer to humans

The substance can affect:

• food consumption;
• body mass;
• fat tissue;
• energy expenditure;
• metabolic signaling

in an animal model.

This may justify further research.

However, this does not mean that effective treatment of obesity in humans has been proven.

Not every product that appears in a weight loss search is a peptide

Online weight management categories can combine chemically different substances, including:

• peptides;
• proteins;
• nanomolecules;
• supplements;
• plant products;
• other compounds.

The classification should be based on the actual active ingredient, and not on the category of the online store or the term used in social media.

The oral form does not specify whether the product is a peptide

The route of administration itself does not define the chemical class.

Some peptide medicines have specially formulated oral formulations.

Other oral medications used in weight control are not peptides.

Studies on oral semaglutide show why formulation and delivery technology require separate evidence [3].

The supplement with peptides is not a substitute for a prescription peptide medication

A supplement that is described as containing peptides can differ significantly from a prescription medication in terms of:

• composition;
• molecular identity;
• destinations;
• formulation;
• exposure;
• regulatory system;
• available clinical studies.

The mere occurrence of the word „peptide” does not create a clinical equivalence.

What did the most important studies actually show?

STEP 1: semaglutide

In the STEP 1 study, randomization was performed. 1961 adults with obesity or overweight and at least one weight-related condition, without diabetes.[1]

After 68 weeks, the average weight change was:

• −14.9% in the semaglutide group;
• −2.4% in the placebo group.

Both groups also participated in a lifestyle intervention.[1]

This is strong evidence regarding the specific intervention used in the conditions of this study.

However, this does not mean that:

• Each person will lose 14.9% kg of body weight;
• every product labeled as semaglutide is equivalent;
• each population will reach the same result;
• Each peptide will cause a similar reduction in body weight.

SURMOUNT-1: tirzepatide

SURMOUNT-1 study involved 2539 adults with obesity or overweight qualifying for it. The study also excluded people with diabetes [2].

After 72 weeks, the mean weight change in the three groups receiving tirzepatide ranged from:

−15.0% to −20.9%

compared to:

−3.1% in the placebo group. [2]

Again, this was a randomized, double-blind clinical trial concerning a specific treatment program.

This was not a study of the general category of „peptidic products”.

Why are STEP 1 and SURMOUNT-1 important?

These studies help explain a large part of the scientific and social interest in peptide drugs used in weight control.

The correct interpretation is:

Specific interventions led to a significant mean reduction in body weight in specific populations in randomized clinical trials.

An incorrect simplification would, however, be:

„peptides cause the loss of 15–20% kg of body weight”.

Such a statement removes information about the product, population, duration of the study, formulation, comparator, and the design of the study.

Does a higher percentage of weight loss automatically mean a better drug?

No.

Comparisons of treatment cannot be reduced to one percentage derived from separate studies.

Effectiveness should be interpreted together with:

• characteristics of the population;
• sometimes the duration of the study;
• adverse effects;
• by interrupting the treatment;
• end points;
• maintaining the effect;
• clinical context.

A higher percentage value in one study does not in itself prove an advantage over another intervention studied under different conditions.

Weight loss and changes in body composition

Body mass does not tell which tissue has changed

The total body mass includes, among other things:

• fat tissue;
• skeletal muscles;
• other non-fatty tissues;
• bones;
• water;
• organs;
• glycogen;
• the content of the alimentary canal.

The decrease in body mass does not mean that the entire change came from fat tissue.

It also does not specify the place from which the fat tissue was lost.

Does weight loss mean the same thing as fat loss?

No.

Weight indicates the total mass of the organism.

It does not allow determining which part of the change concerned the fat tissue, the lean mass, or the water.

Therefore, the results of STEP 1 and SURMOUNT-1 should primarily be interpreted in accordance with their endpoints regarding body mass, unless a separate body composition analysis is discussed.[1][2]

The claim regarding the specific loss of fat requires proper measurement of body composition.

The composition of the body answers another question

Among other things, DXA and imaging methods are used to estimate body composition.

They allow them to try to distinguish between different tissue regions.

However, body composition analysis should be interpreted separately from the main weight measurement, as it may only include a portion of the participants.

Lean mass does not only mean muscle

This is a particularly important distinction:

lean mass ≠ exclusively skeletal muscles.

It also includes other tissues that do not contain fat.

Changes can also affect its measurements:

• hydration;
• glycogen;
• organs;
• connective tissues;
• other fat-free ranges.

Therefore, reductions in lean mass should not be automatically described as identical muscle loss.

Does losing non-fat mass mean losing the same amount of muscle?

No.

Lean mass includes more than just skeletal muscles and can change, among other things, under the influence of hydration.

It also does not directly measure the strength, quality, or function of the muscles.

Therefore, conclusions regarding muscle preservation require appropriate data on body composition and function.

Body composition does not automatically determine function

Even precise measurement of tissues does not directly indicate:

• force;
• strength;
• mobility;
• power;
• physical fitness;
• quality of the muscles.

These elements require separate functional measurements.

Why do claims about „muscle protection” require their own evidence?

The product can reduce body weight without showing that it maintains all aspects of muscle health.

An assessment of such a claim may require research on:

• body composition;
• skeletal muscles;
• forces;
• the functioning of the physical body;
• changes over time.

Loss of fat does not automatically mean maintaining a completely fat-free mass

Even if the majority of the lost weight comes from fat, this does not automatically mean:

„There was no loss of muscle.”.

These are two different claims.

Can a body composition test prove strength performance?

No.

Body composition measurements estimate the amount of specific tissues.

Strength, on the other hand, is a functional result.

Neurological, mechanical, training, and nutritional factors also influence the force.

Therefore, the claim of maintaining muscle function requires direct functional measurements.

Percentage change and percentage points

These terms are often confused in descriptions of studies concerning weight reduction.

Percentage change

It describes the change relative to a specific initial value.

If the reference point is the initial body mass, a decrease of 12% means a change corresponding to 12% of that value.

Percentage points

The difference between the two percentage values is expressed in percentage points.

For example:

if one group loses 12% of its initial body weight, and the other 3%, the difference between the averages is:

9 percentage points.

That doesn't change the fact that the reduction in the first group is 12%.

This is an arithmetic example, not the result of a specific clinical study.

Why is this important in studies concerning discontinuation of treatment?

In withdrawal studies, the new reference point may be the body weight at the time of randomization, after previous weight loss.

The later percentage increase can therefore be calculated relative to this lower value.

It should not simply be subtracted from the previous percentage calculated relative to the initial initial mass.

The criteria are different.

Average group performance versus individual performance

The average of the survey does not show the full range of the participants' responses.

Individual people may experience:

• a change greater than the average;
• minor change;
• a slight change;
• re-increase in body weight;
• adverse effects;
• Discontinuation of treatment.

Does the average of the study predict the outcome of a particular person?

No.

The average describes the group experience and can hide significant differences between the participants.

The reported result is also influenced by qualification criteria, protocol compliance, parallel care, missing data, and statistical methods used.

STEP 1 therefore presents the result at the group level under specific conditions, rather than a guaranteed result for each individual.[1]

Response thresholds provide additional information

The studies may report the percentage of participants achieving a certain level of weight reduction.

This helps to see the distribution of the answers.

The interpretation still depends on:

• the analyzed population;
• missing data;
• interruption of treatment;
• statistical methods.

The best-performing group does not represent the entire study

Media headlines may focus on the group achieving the highest average reduction.

It is not the same as:

• the average result of all groups;
• the result of each participant;
• a forecast for a specific person.

Estimands are important

Modern studies can report several endpoints, that is, precisely defined questions regarding the effect of the treatment.

One analysis might ask:

What happened regardless of the interruption of treatment?

Another one can analyze:

What happened when it was decided to continue the treatment or follow the protocol?

Both can provide useful information.

Providing only a more favorable result without explaining what it actually represents can be misleading.

Weight reduction and clinical outcomes

Weight loss may have clinical significance.

However, it is not the same thing as directly proving a smaller number:

• heart attacks;
• strokes;
• disabilities;
• hospitalization;
• deaths.

Such results require separate studies.

SELECT and cardiovascular outcomes

The SELECT study included 17,604 people aged at least 45 years with a known cardiovascular disease and overweight or obesity, but without diabetes. [4]

In the medium-term observation period of 39.8 months The main composite endpoint for cardiovascular events occurred in:

• 6.5% people in the semaglutide group;
• 8.0% people in the placebo group.

The risk factor amounted to 0,80. [4]

What does SELECT confirm?

The study provides data on cardiovascular outcomes in the studied population.

It included the following people:

• with a known cardiovascular disease;
• with overweight or obesity;
• without diabetes;
• meeting certain qualification criteria.

What does SELECT not confirm?

It does not automatically mean the same absolute benefit for:

• young adults;
• people without a recognized cardiovascular disease;
• populations at lower risk;
• to anyone who wants to reduce their body weight;
• people using other peptide interventions.

Does the cardiovascular benefit apply to anyone who wants to lose weight?

No.

SELECT was aimed at people with a specific risk profile.

The absolute cardiovascular benefit may strongly depend on the initial risk and the length of observation period.

Therefore, the boundaries of the population studied should remain part of the proposal.[4]

Relative and absolute effects are not the same thing

The risk factor of 0.80 describes the relative comparison of the time to the occurrence of the event according to the analysis of the study.

The observed rates of events differed, however, by:

1.5 percentage point.

These are related but different statistics.

They should not be interpreted as a reduction in cardiovascular events by 20 percentage points.

Does the loss of weight itself lead to improvements in cardiovascular outcomes?

No.

Weight reduction may be clinically significant, but cardiovascular events require direct measurement.

In SELECT, they were evaluated directly, instead of being inferred solely based on changes in body weight.[4]

Approved medicines and research claims

The approval applies to a specific product

In the European Union, the EMA describes the indications for weight management for the semaglutide-containing drug Wegovy and the tirzepatide-containing Mounjaro [5] [6].

Current information regarding Wegovy includes formulations with various population restrictions.

This shows why the information about approval should specify:

• product;
• the active substance;
• a formulation when it matters;
• indication;
• the population;
• jurisdiction;
• the date.

The statement alone:

„peptides are approved for weight loss”

It is too wide.

Example from the United States

The FDA’s 2023 notice documented the approval of Zepbound, containing tirzepatide, for the long-term management of body weight in eligible adults.[7]

The historical communication describes a specific regulatory decision.

If the current details of the indications are important, you should check the current full information about the product.

Regulatory status may change

Regulatory authorities may:

• to expand the indications;
• approve new formulations;
• update product information;
• add warnings;
• introduce other regulatory changes.

Therefore, the current status should be checked with the appropriate regulator.

Experimental results should remain described as experimental.

Retatrutyd

The phase 2 study regarding retatridine involved 338 adults, and the results regarding body weight were observed by 48 weeks. [8]

Significant weight reduction was observed in the studied groups.

Adverse reactions have also been reported, including gastrointestinal complaints and an increase in heart rate.[8]

What did the study show?

It showed that a specific intervention using retatridate:

• it has been tested in humans;
• led to measurable changes in body weight;
• provided safety data during the study.

What the study did not show?

The publication of the results of phase 2 is not the same as the product being approved for sale.

According to the current FDA communication, retatrutide and cagrilintide are not components of drugs approved by the FDA.[9]

This is information related to the United States.

Does Phase 2 testing mean that the compound is almost approved?

No.

Phase 2 may provide important data on efficacy and safety in humans, but further studies and regulatory assessment may still be necessary.

Not all substances with promising results in early development phases ultimately receive authorization.

Retrospective results should therefore be considered important experimental data, and not a guarantee of future approval.[8][9]

„Promising” and „experimental” do not exclude each other

The term “experimental” does not mean ignoring interesting results.

At the same time, promising clinical data do not justify presenting it as a fixed, approved treatment.

Both facts can be presented simultaneously.

The tested drug and a similarly named product are not automatically equivalent.

A clinical trial evaluates a specific intervention.

It includes more than just the name of the molecule itself.

They may have significance:

• chemical identity;
• formulation;
• the method of production;
• stability;
• concentration;
• packaging;
• route of administration;
• quality control.

The very name of the active substance does not prove equivalence

Another product using the same or similar name of the ingredient may not have a confirmed equivalence in terms of:

• identity;
• purity;
• stability;
• exposure;
• pharmacokinetics;
• quality;
• clinical results.

High purity does not mean the same evidence as the drug used in the study.

Purity is an analytical parameter, not a proof of therapeutic equivalence.

Ready clinical medicine is also defined by factors such as:

• formulation;
• production;
• stability;
• the amount of substance;
• route of administration;
• quality control system.

High-purity research material does not therefore automatically translate into clinical results for the regulated finished product.

„Research use only” does not mean that the product has been clinically verified.

The designation of a product as intended for research describes its research context.

Does not confirm:

• clinical validation;
• authorization;
• usability for human use;
• equivalence with the product used in the clinical trial.

User reviews do not replace clinical studies

Individual experiences can be real.

However, they are not equivalent to controlled evidence.

Body weight can change under the influence of many factors, including:

• the amount of energy consumed;
• physical activity;
• illnesses;
• other medications;
• water management;
• the way of feeding;
• of sleep;
• parallel treatment;
• natural fluctuations.

The user's opinion usually does not allow us to separate these factors.

The „before and after” photos have additional limitations

Appearance can be influenced by:

• attitude;
• clothes;
• lighting;
• camera angle;
• distance;
• hydration;
• moment of taking the photo.

The photographs also do not allow us to determine:

• body composition;
• the identity of the product;
• causal relationship;
• the durability of the effect.

A credible clinical claim should therefore lead to appropriate research, and not just to a collection of positive stories.

The study population determines the scope of the conclusions

STEP 1 and SURMOUNT-1 primarily included adults meeting specific criteria of obesity or overweight and excluded people with diabetes.[1][2]

The average results from these studies should not be automatically applied to groups that were not represented in them.

These may include:

• people with diabetes;
• young people;
• pregnant women;
• elderly people with fragility syndrome;
• people who do not meet the criteria regarding body weight.

Can the results for adults without diabetes be directly applied to other groups?

Not automatically.

The inclusion criteria specify the population represented by the results obtained.

Other groups may differ in terms of:

• responses to treatment;
• risks;
• approved indications;
• other clinical conditions.

Qualification criteria are part of the evidence

They may include:

• age;
• initial BMI;
• co-existing diseases;
• previous treatment;
• the medications used;
• other diseases.

All these elements affect the possibility of generalizing the results.

The treatment time and the observation time answer other questions

The study can observe the participants:

• during active treatment;
• after the end of treatment;
• in both of these periods.

Duration of treatment

It shows what happened during the use of the intervention.

Maintaining the effect

It answers the question of whether the change persisted over time.

The period after discontinuation

It shows what happened after the intervention ended or was changed.

Does „maintained weight loss” mean a permanent effect?

No.

In scientific publications, the term „maintained” usually means that the effect was still observed at a certain point in time.

It does not mean:

„forever”.

A result that persists for 68 or 72 weeks should be described in relation to that period.

What do the studies on discontinuation of treatment show?

Extension of STEP 1

In the extension of STEP 1, post-treatment and structured lifestyle intervention were observed. 327 participants. [10]

A year later, the people previously assigned to semaglutide regained an average of about two-thirds of the previously lost body weight. [10]

This result is significant, but it requires context.

Study:

• it included part of the original population;
• it had an exploratory nature;
• was observed by the participants after the end of the treatment being studied;
• It also ended structured intervention regarding lifestyle.

Therefore, the result cannot be reduced to simply discontinuing the medication.

SURMOUNT-4

SURMOUNT-4 applied a different design.

After the initial 36-week period of use of tirzepatide 670 participants They were randomly assigned to continue treatment or switch to placebo for a further 52 weeks. [11]

From the moment of randomization to week 88, the average body weight changed by:

• −5.5% with continued tirzepatide;
• +14.0% after switching to placebo. [11]

Why is a reference point important?

These percentages refer to body weight at the time of randomization, that is, after the initial treatment period.

They should not be directly combined with the previous percentage values calculated relative to the original initial mass.

Can body weight increase after the end of treatment?

Yes.

In discontinuation studies, a rebound increase in body weight was observed.

STEP 1 extension and SURMOUNT-4 had different designs, but both show why initial weight reduction and its subsequent maintenance are separate questions. [10] [11]

This does not mean that every person will have the same course of action.

Does the renewed increase in body weight mean that the previous test result was false?

No.

Intervention can have a measurable effect during its implementation, even if part of that effect diminishes after its completion.

SURMOUNT-4 directly analyzed the difference between continuing treatment and switching to placebo. [11]

The renewed increase in body weight changes the interpretation of the durability of the effect, but does not invalidate the result observed during treatment.

Resignation and tolerance affect the interpretation of the results

The individuals included in the study may differ from the participants who chose not to participate.

The analysis of people who finish the study may give a different picture.

If the analysis only includes people who are still receiving treatment, the result may differ from the analysis that takes into account the consequences of discontinuing therapy.

The reason for the interruption of treatment is important

Discontinuation due to adverse reactions is part of the actual outcome of the treatment.

It should not be overlooked during the evaluation of effectiveness.

Good reporting should therefore explain:

• how many people were randomized;
• how many have completed treatment;
• for how many were available measurements of the results;
• why the participants interrupted their participation;
• how the missing data was handled.

Comparing different studies requires caution

STEP 1 and SURMOUNT-1 differed, among other things:

• intervention;
• sometimes duration;
• characteristics of the participants;
• procedures;
• support programs;
• statistical analyses. [1] [2]

Placing the largest percentage values side by side shows the results of individual publications.

However, it does not create a randomized study directly comparing the two drugs.

Do separate studies show which drug is „the best”?

Not in a direct way.

Head-to-head comparisons are more informative for assessing the relative effectiveness if:

• the populations are suitable;
• the formulations are comparable;
• the endpoints are consistent;
• the treatment conditions are appropriately adjusted.

Intermediate analyses can be useful, but they require assumptions regarding the comparability of different studies.

Security and loopholes in evidence

Effective intervention can still cause adverse effects

In the most important studies on weight control, adverse effects on the gastrointestinal tract were reported in parallel with weight loss. [1] [2]

Some participants discontinued treatment due to adverse reactions.

This information belongs to the same assessment of evidence as effectiveness.

„Mainly mild or moderate” does not mean „without risk”

If the majority of adverse reactions were classified as mild or moderate, this does not mean that:

• each event was small;
• serious incidents are impossible;
• The drug is suitable for everyone.

Does a large average weight reduction make the side effects insignificant?

No.

Effectiveness and tolerance are two parts of the same evaluation.

A large, medium-sized weight loss does not eliminate adverse effects or confirm the appropriateness of the intervention for each individual.

A reliable summary should present both the potential benefits and the potential harms.

There is no single safety profile for „weight loss peptides”

The category is too broad.

Safety depends on:

• a specific molecule;
• mechanism;
• formulation;
• exposure;
• population;
• medications being used concurrently;
• individual clinical situation.

The size and length of the study limit the ability to detect the risk

A small or short-term study may not detect it reliably:

• rare adverse reactions;
• delayed effects;
• very long-term consequences;
• effects occurring in populations excluded from the study.

The absence of a specific problem in a limited study is not proof that such a problem is impossible.

„Long-term effects” is not just one question

The term can refer to:

• further reduction of body weight;
• maintenance of the gained mass;
• body composition;
• cardiovascular events;
• the functioning of the physical body;
• quality of life;
• adverse effects;
• the situation after the end of treatment.

One study rarely answers all these questions.

SELECT provides longer data on cardiovascular outcomes in a specific population. [4]

STEP 1 extension and SURMOUNT-4, on the other hand, provide information regarding the maintenance of the effect and withdrawal. [10] [11]

These studies complement each other.

However, this does not mean that all questions regarding long-term effects have been resolved.

Weight loss, fat loss and body contouring are different concepts

Weight loss

Reduction of the total body mass.

Loss of fat

Reduction of the amount of fat tissue.

Change in the non-fat mass

Change in the mass of tissues other than fat. This is not the same as the change in skeletal muscle mass.

Reconstruction of the body

A broader term describing the change in the proportion of fat tissue and non-fat mass.

Maintaining functionality

Maintaining or improving:

• forces;
• mobility;
• strength;
• other functional parameters.

A study measuring only body weight cannot automatically confirm all of these effects.

How to evaluate the claim regarding the peptide for weight loss?

The evidence supports specific conclusions regarding specific interventions.

They do not support treating all peptides as a single universal category of weight loss supplements.

Simple hierarchy of evidence regarding peptides and weight reduction

Mechanistic evidence

They show that the molecule affects a pathway related to appetite or metabolism.

They confirm the biological plausibility of the hypothesis.

They do not prove weight reduction in humans.

Animal studies

They can show changes:

• food consumption;
• body mass;
• fat tissue;
• metabolism.

These are still preliminary data.

Early research involving humans

They can provide information about:

• exposure;
• tolerance;
• initial effectiveness;
• short-term results.

They may justify conducting larger studies.

Randomized controlled studies

They provide stronger evidence regarding:

• changes in body weight;
• adverse effects;
• differences between the groups

in a specific population.

Long-term studies and studies of clinical outcomes

They may answer additional questions regarding:

• cardiovascular events;
• maintaining the effect;
• a longer period of observation.

Regulatory authorization

It applies to a specific product and the indication in a specific jurisdiction.

These levels should not be combined just because they all relate to peptide substances.

Frequently asked questions

Do all peptides affect body weight?

No. Peptides perform very different biological functions, and their activity depends on the structure of the molecule, receptors, exposure, formulation, and biological target. The most important studies regarding weight reduction discussed in this article analyzed semaglutide and tirzepatide, not the general category of peptides. [1] [2] Therefore, their results cannot be extrapolated to the unrelated substance simply because it is also a peptide.

Can a peptide supplement replicate the results of a prescription drug?

This cannot be assumed. The supplement may differ from the drug in terms of composition, molecular identity, formulation, stability, exposure, quality control, and available studies. The development of oral semaglutide demonstrates well why the peptide’s own name does not confirm equivalent clinical activity.[3] Replicating the results of a prescription drug study would require appropriate evidence regarding the specific product.

Do the „before and after” photos confirm the loss of fat?

No. Photos can document the appearance, but they do not measure body composition. Appearance is influenced by factors such as lighting, clothing, posture, camera angle, hydration, and the moment of photography. They also do not allow for reliable determination of the product’s identity, causal relationship, or durability of the effect. In large randomized studies, standardized measurements of body mass were used and controlled comparisons, rather than promotional photos. [1] [2]

Does greater weight loss always mean greater fat loss?

No. A total change in body weight can include changes in fat mass, non-fat mass, and water. The relationship between total weight reduction and fat loss depends on the actual changes in body composition. Therefore, the claim regarding specific fat mass requires appropriate measurements.

Does the commercial availability of the peptide mean that it has been approved as a weight loss product?

No. Commercial availability, regulatory authorization, product quality, and clinical evidence are separate issues. A substance can be advertised or sold while remaining an experimental compound or a product without evidence equivalent to an approved drug. The current status should be verified with the appropriate regulator.

Can the results regarding semaglutide or tirzepatide be used as evidence for another „weight loss peptide”?

No. The most important clinical studies support specific conclusions regarding semaglutide and tirzepatide under the conditions in which they were studied. [1] [2] The unrelated peptide requires its own data. Transferring results from recognized drugs to another substance just because it is also classified as a peptide is a mistake in categorizing.

Limitations of current evidence

The first limitation is the specificity of the product.

The strongest evidence relates to specific drugs, not peptides as a single chemical class.

The second is specificity of the population.

Large studies use specific criteria for qualification, and their average results cannot be automatically transferred to unstudied populations.

The third is duration of the studies.

Even large studies do not answer all the questions about the whole of life.

The fourth is maintaining the effect.

The initial weight reduction does not automatically determine what will happen after the end of treatment.

The fifth is body composition.

The actual body mass does not allow for an exact determination of which part of the change was related to fat or skeletal muscle.

He is sixth. functional interpretation.

The change in lean mass does not directly affect strength, mobility, or the quality of the muscles.

He is seventh. comparing different studies.

Separate studies do not automatically determine which intervention is more effective than the other.

The eighth is Regulatory diversity.

Authorizations and designations may vary between jurisdictions and change over time.

The ninth is uncertainty associated with experimental relationships.

Promising results from early studies may coexist with unresolved questions regarding long-term safety, efficacy, and future regulatory status.

The tenth is product equivalence.

An unexamined preparation cannot automatically take over the evidence regarding a clinically tested finished product simply because it uses a similar name for the active ingredient.

Ultimately, the term itself „peptides for weight loss” it is too broad to constitute a scientific conclusion.

This is a search category.

Evidence still needs to be analyzed separately for each molecule, each product, indication and study.

Summary

Peptide drugs have become an important part of modern research into weight control because some specific molecules can affect the signaling systems associated with appetite and metabolic regulation.

Large randomized studies have shown a significant average reduction in body weight for certain interventions.

In STEP 1, semaglutide was associated with a mean change in body weight of −14.9% after 68 weeks, Compared to −2.4% in the placebo group, in a specific study population.[1]

In SURMOUNT-1, the average weight reduction in the tirzepatide groups was between −15.0% to −20.9% after 72 weeks, Compared to −3.1% in the placebo group. [2]

SELECT provided separate data on cardiovascular outcomes associated with semaglutide in a selected high-risk population with known cardiovascular disease and overweight or obesity, without diabetes. [4]

Studies on withdrawal provide another part of the picture.

The STEP 1 extension and SURMOUNT-4 show that the initial reduction in body weight and the subsequent maintenance of the effect are different outcomes, and that after changing or discontinuing treatment, a rebound increase in body weight may occur. [10] [11]

These results are important.

However, this does not mean that:

• each peptide causes weight loss;
• every product containing a peptide is equivalent;
• each person will achieve the average observed in the study;
• all the lost mass comes from adipose tissue;
• the change in lean mass is identical to the loss of muscle;
• the weight reduction is permanent;
• any loss of mass provides an identical cardiovascular benefit;
• experimental compounds are equivalent to approved drugs;
• products with a similar name reproduce the results of regulated formulations.

A scientifically justified assessment must therefore relate to a specific product and a specific result.

In the case of any claim regarding a „weight loss peptide,” it is worth asking:

Which exact molecule was tested?

What formulation was used?

Who was studied?

What was the comparator?

How big was the change in body weight?

Was the body composition analyzed?

How long did the observation last?

What happened after the end or change of treatment?

What adverse reactions and cases of discontinuation of treatment have been reported?

What clinical results other than body weight have actually been measured?

What is the current regulatory status of a specific product in a given jurisdiction?

Breaking down these questions makes the interpretation of the evidence much more transparent.

The current scientific literature confirms significant weight management effects for certain specifically studied peptide drugs.

However, it does not confirm the treatment. „weight loss peptides” as a single universally effective and interchangeable category.

Disclaimer

The article is purely educational and scientifically informational in nature. It does not constitute medical advice, diagnosis, advice regarding weight loss or weight management, guidance regarding the selection of treatment, prescription of medications, dosage, preparation or administration of substances. It is also not a recommendation to use any peptide, prescription drug, prescription preparation, experimental compound, supplement or research material.

Clinical trial results describe results observed in specific populations and should not be interpreted as guaranteed results for a specific individual. Authorizations, indications, warnings, and product information may vary among jurisdictions and change over time.

Those making decisions regarding obesity, body mass, metabolic health, cardiovascular health, or prescription medications should use the current information from relevant regulatory authorities and consult with a properly qualified health protection professional.

References

[1] Wilding, J. P. H., Batterham, R. L., Calanna, S., Davies, M., Van Gaal, L. F., Lingvay, I., McGowan, B. M., Rosenstock, J., Tran, M. T. D., Wadden, T. A., Wharton, S., Yokote, K., Zeuthen, N., Kushner, R. F., and STEP 1 Study Group (2021). Once-weekly semaglutide in adults with overweight or obesity. The New England Journal of Medicine, 384(11), 989–1002. 10.1056/NEJMoa2032183.

[2] Jastreboff, A. M., Aronne, L. J., Ahmad, N. N., Wharton, S., Connery, L., Alves, B., Kiyosue, A., Zhang, S., Liu, B., Bunck, M. C., Stefanski, A., & SURMOUNT-1 Investigators. (2022). Tirzepatide once weekly for the treatment of obesity. The New England Journal of Medicine, 387(3), 205–216. 10.1056/NEJMoa2206038.

[3] Lewis, A. L., McEntee, N., Holland, J., & Patel, A. (2022). Development and approval of Rybelsus (oral semaglutide): ushering in a new era in peptide delivery. Drug Delivery and Translational Research, 12(1), 1–6. 10.1007/s13346-021-01000-w.

[4] Lincoff, A. M., Brown-Frandsen, K., Colhoun, H. M., Deanfield, J., Emerson, S. S., Esbjerg, S., Hardt-Lindberg, S., Hovingh, G. K., Kahn, S. E., Kushner, R. F., Lingvay, I., Oral, T. K., Michelsen, M. M., Plutzky, J., Tornøe, C. W., Ryan, D. H., & SELECT Trial Investigators. (2023). Semaglutide and cardiovascular outcomes in obesity without diabetes. The New England Journal of Medicine, 389(24), 2221–2232. 10.1056/NEJMoa2307563.

[5] European Medicines Agency. (n.d.). Wegovy: European public assessment report. Retrieved September 20, 2026, from Wegovy: European public assessment report.

[6] European Medicines Agency. (n.d.). Mounjaro: European public assessment report. Retrieved September 20, 2026, from Mounjaro: European public assessment report.

[7] U.S. Food and Drug Administration. (2023, November 8). FDA approves new medication for chronic weight management. FDA approves new medication for chronic weight management.

[8] Jastreboff, A. M., Kaplan, L. M., Frías, J. P., Wu, Q., Du, Y., Gurbuz, S., Coskun, T., Haupt, A., Milicevic, Z., Hartman, M. L., & Retatrutide Phase 2 Obesity Trial Investigators. (2023). Retatrutide, a triple-hormone-receptor agonist for obesity—A phase 2 trial. The New England Journal of Medicine, 389(6), 514–526. 10.1056/NEJMoa2301972.

[9] U.S. Food and Drug Administration. (n.d.). FDA’s concerns with unapproved GLP-1 drugs used for weight loss. Retrieved September 20, 2026, from FDA’s concerns with unapproved GLP-1 drugs used for weight loss.

[10] Wilding, J. P. H., Batterham, R. L., Davies, M., Van Gaal, L. F., Kandler, K., Konakli, K., Lingvay, I., McGowan, B. M., Oral, T. K., Rosenstock, J., Wadden, T. A., Wharton, S., Yokote, K., Kushner, R. F., & STEP 1 Study Group. (2022). Weight regain and cardiometabolic effects after withdrawal of semaglutide: The STEP 1 trial extension. Diabetes, Obesity and Metabolism, 24(8), 1553–1564. 10.1111/dom.14725.

[11] Aronne, L. J., Sattar, N., Horn, D. B., Bays, H. E., Wharton, S., Lin, W. Y., Ahmad, N. N., Zhang, S., Liao, R., Bunck, M. C., Jouravskaya, I., Murphy, M. A., & SURMOUNT-4 Investigators. (2024). Continued treatment with tirzepatide for maintenance of weight reduction in adults with obesity: The SURMOUNT-4 randomized clinical trial. JAMA, 331(1), 38–48. 10.1001/jama.2023.24945.