Before using any NAD+-related product, it is worth understanding what published human safety data actually shows. Safety results also vary depending on the route of administration, so oral capsules, transdermal patches, injections, and intravenous infusions should not be treated as having an identical side effect profile. This guide compiles the results of human studies, discusses potential contraindications and gaps in drug interaction data, and explains what can realistically be said about „long-term safety,” given that clinical trials in this area are still relatively new.
Common side effects depending on the form: oral, patches, injections, and IV
Oral NAD+ precursors, such as NR and NMN, have shown generally good tolerance in multiple randomized, placebo-controlled human trials.
In an 8-week study of nicotinamide riboside at doses up to 1000 mg per day, no significant difference in the incidence of adverse events was found between the NR and placebo groups, and no serious adverse events were reported [1].
A multiple-dose study evaluating the combination of NR and pterostilbene also found that the intervention was well tolerated for the duration of the study [2].
Human safety studies on NMN have similarly shown no severe adverse effects at doses up to 1250 mg daily for 4 weeks [3], as well as after single doses up to 500 mg [4].
When mild adverse events were reported in these studies, they typically included symptoms such as headache, mild gastrointestinal discomfort, and fatigue. Importantly, some of these symptoms also occurred in participants receiving placebo at a similar frequency, making it difficult to determine whether each reported symptom was directly caused by the test compound [1,5].
At higher tested NR doses in the phase I safety study, 3000 mg of nicotinamide riboside per day was administered to individuals with Parkinson's disease for 30 days, and the intervention was reported to be tolerated for the duration of the study [6].
Transdermal patches have a significantly smaller human safety database.
As discussed in our separate guide on NAD+ patches, controlled human trial data on this route of administration are limited to a small pilot study. In that study, NAD+ patches using iontophoresis caused mild and transient skin irritation in approximately 25% participants [7].
This is a local skin effect, rather than a systemic symptom observed with some other routes of administration.
For subcutaneous or intramuscular NAD+ injections, controlled human study data characterizing side effects in detail remain limited.
As discussed in our injection guide, additional safety considerations arise from the method of administration itself. These include local pain or irritation, bruising, injection site reactions, and the potential for infection if aseptic preparation and administration principles are not followed.
These risks must be distinguished from the potential pharmacological effects of NAD+ itself.
Intravenous administration produced the most noticeable route-specific tolerance signal discussed in this guide.
A retrospective real-world study comparing commercially administered intravenous NAD+ with intravenous nicotinamide riboside found that individuals receiving IV NAD+ experienced gastrointestinal symptoms, including nausea, and cardiac-related symptoms, including palpitations, more frequently than those receiving IV NR in the same clinical settings [8].
This is an important route-specific observation.
It suggests that direct intravenous administration of NAD+ may have a different tolerance profile than oral NAD+ precursors and the intravenous administration of related precursor compounds.
However, because these results came from a retrospective real-world study rather than a randomized controlled trial, they should be considered as a safety signal rather than conclusive comparative evidence.
Contraindications and who should avoid NAD+
Available research does not provide a complete list of formal contraindications for every NAD+ product or every route of administration. However, there are groups that have been excluded from clinical trials or require greater caution for other reasons.
Pregnant or breastfeeding individuals have not been adequately studied in the human NAD+ research referenced in our guides.
Available studies generally did not include pregnant or breastfeeding participants, therefore safety data for these groups are lacking.
For this reason, the use of NAD+ or NAD+ precursors during pregnancy or breastfeeding should be discussed with a qualified healthcare professional before use.
Individuals with a personal or family history of cancer also require a more individualized approach.
As discussed in more detail in our disease research guide, one preclinical study showed that nicotinamide riboside supplementation was associated with an increased incidence of tumors and brain metastases in a mouse model of triple-negative breast cancer [9].
This result was not confirmed in humans and came from a specific animal model.
At the same time, NAD+ metabolism has a complex relationship with cancer biology, as rapidly dividing cancer cells can rely heavily on NAD+ salvage pathways to support metabolism and growth.
For this reason, general safety results obtained in healthy individuals or in non-cancer populations should not be automatically extrapolated to individuals with active cancer, a history of cancer, or a potentially increased cancer risk.
Individuals in such situations should discuss NAD+-related supplementation with their oncologist or another appropriately qualified physician.
Children and adolescents represent another group for whom dedicated safety data remain limited.
Most human studies on NR, NMN, and related compounds have involved adults, often middle-aged or older.
Pediatric dosing, safety, impact on development, and long-term effects have not been adequately established.
Individuals with certain cardiovascular diseases may also require greater caution, especially when considering intravenous or injectable NAD+.
This applies primarily to heart-related symptoms reported in the retrospective study IV [8].
This should be interpreted as a route-specific issue, rather than a universal contraindication applying equally to all forms of NAD+ and its precursors.
People with a diagnosed allergy or hypersensitivity to the ingredients of a specific product should also avoid those ingredients.
Potential allergens or irritants may include inactive ingredients, preservatives, excipients, adhesives used in patches, or components present in injection formulations.
In injectable products, some bacteriostatic diluents may contain preservatives such as benzyl alcohol, which is not suitable for everyone.
Does NAD+ interact with other supplements or medications?
Research on drug interactions represents a significant gap in the current NAD+ literature.
Dedicated human studies evaluating the interactions of NAD+ precursors with commonly prescribed medications are limited.
Many clinical trials limited the potential for confounding results by excluding participants taking specific medications, rather than intentionally investigating whether these medications interact with NR, NMN, or other NAD+-related compounds.
The absence of reported interactions in such studies should therefore not be interpreted as evidence that clinically significant interactions do not occur.
Some caution can be inferred from the biological pathways affected by NAD+ metabolism.
For example, some human studies have reported effects on glucose regulation and insulin sensitivity, although the results have not been consistent across all studies.
Individuals using insulin or other glucose-lowering medications should therefore discuss the use of NAD+ precursors with their doctor, especially if there is a possibility of changes in blood glucose levels or insulin sensitivity.
Similarly, in some NR studies, cardiovascular and vascular parameters were evaluated, including blood pressure-related outcomes.
Therefore, individuals taking antihypertensive or other cardiovascular medications may benefit from a professional evaluation before starting a NAD+-related supplement.
Research on combining it with other supplements is also limited.
There are no dedicated controlled studies establishing the safety or efficacy of combining NAD+ precursors with many products frequently promoted alongside them, such as resveratrol, collagen supplements, or other compounds associated with longevity.
Some products have been studied in specific combinations, but these results should not be automatically generalized to every formulation or every combination of supplements.
Claims that two products exhibit a specific „synergistic effect” should therefore be treated with caution, unless the given combination has been directly tested.
Because formal interaction studies remain limited, the most reliable approach is a review of the complete list of medications and supplements by a physician or pharmacist.
Is NAD+ safe long-term? What is actually known?
The term „long-term safety” requires careful use in relation to NAD+ precursors.
Human studies typically ranged from single-dose studies to several weeks or months, with some studies covering a period of about one year [1,2,3,6].
This provides useful information on short-term and medium-term tolerance.
However, it does not provide the same kind of multi-year safety data that is available for drugs or supplements used and studied for many decades.
Within the previously studied periods, the safety results for oral NR and NMN have been generally reassuring.
Many independent research teams have tested various compounds and doses without finding a repeatable pattern of serious adverse effects attributed to NR or NMN [1,2,3,4,5,6].
However, the absence of significant safety signals for weeks or months does not mean that continuous use for many years is safe.
A longer exposure could theoretically reveal rare, cumulative, metabolic, or population-specific effects that shorter clinical trials are not designed to detect.
Research continues to evolve into more targeted populations and outcome categories.
For example, a systematic review and meta-analysis evaluating NMN and NR regarding skeletal muscle parameters in older adults reflect the growing base of clinical research focused on specific age-related issues such as sarcopenia and muscle function [10].
A growing body of research is providing more information on shorter-term use in selected populations, but it should not be confused with actual long-term safety surveillance.
The most precise conclusion is that the safety data for short- and medium-term oral NR and NMN are generally reassuring across multiple human studies, while the actual safety of continuous, multi-year use remains insufficiently established.
The issue of cancer: what do studies show and what do they not show?
The relationship between NAD+ metabolism and cancer is complex and should not be reduced to claims that NAD+ „causes cancer” or „prevents cancer.”.
Cancer cells often modify their metabolic pathways to support rapid proliferation.
In several types of cancer, the activity of the NAD+ salvage pathway, particularly involving the NAMPT enzyme, may be increased.
For this reason, NAMPT inhibitors have been investigated as potential anti-cancer strategies.
This shows that some cancer cells can be heavily dependent on NAD+ metabolism.
However, this does not mean that NAD+ itself is inherently carcinogenic to healthy tissues.
At the same time, there are preclinical results that justify caution.
In one animal study using a specialized imaging method, nicotinamide riboside supplementation was associated with an increased tumor incidence and a higher number of brain metastases in a mouse model of triple-negative breast cancer [9].
This is a published result and should not be ignored.
However, it was obtained in a specific animal tumor model and no comparable effect has been demonstrated in humans.
Animal tumor models also differ significantly from typical human supplementation conditions.
Current evidence therefore does not support the simple conclusion that NAD+ supplementation causes cancer.
They also do not show that NAD+ supplementation prevents cancer.
This relationship may depend on factors such as cell type, tumor biology, NAD+ metabolism pathways, disease stage, and potentially the specific precursor or type of intervention studied.
Individuals with active cancer, a history of cancer, or a strong family history of cancer should therefore not base their decisions solely on general safety data obtained from the general population.
An individual consultation with an oncologist or other qualified healthcare professional is more appropriate, as many NAD+ studies were not designed to assess cancer incidence, recurrence, metastasis, or long-term oncological outcomes.
When to stop use and consult a doctor?
Medical evaluation may be indicated if new or persistent symptoms develop after starting an NAD+-related product.
Persistent or worsening gastrointestinal symptoms, such as nausea, vomiting, or significant abdominal discomfort, should be discussed with a healthcare professional, especially if they began after the introduction of a new supplement or therapy.
Chest pain, heart palpitations, an unusually fast or irregular heartbeat, or other cardiovascular symptoms require increased caution.
This is particularly important during or after intravenous or injection administration of NAD+, as heart-related symptoms were reported more frequently with IV NAD+ in the retrospective study discussed previously [8].
Symptoms suggesting an allergic reaction, including a widespread rash, swelling of the face or throat, wheezing, or difficulty breathing, require prompt medical evaluation.
Persistent or worsening reactions at the patch or injection site should also be evaluated.
Local redness or irritation can sometimes be mild and temporary, but increasing pain, swelling, warmth, discharge, expanding redness, or systemic symptoms may indicate a more serious reaction or infection.
Every new, unexplained symptom appearing after the introduction of a new NAD+-related product should also be considered in the context of other supplements, medications, and existing medical conditions.
Because dedicated interaction data is limited, an unexpected symptom cannot always be definitively attributed to NAD+ itself or separated from possible drug interactions without clinical evaluation.
Individuals with a personal or family history of cancer, pregnant or breastfeeding women, people with chronic cardiovascular diseases or metabolic disorders, and those taking multiple medications may benefit from discussing the use of NAD+ with a healthcare professional before starting, rather than waiting for an adverse effect to occur.
Limitations of current evidence
- Actual long-term human safety data regarding regular supplementation with NAD+ precursors are still unavailable. Most published studies cover periods ranging from a single dose to several weeks or months, and some lasted about one year [1,2,3,6].
- Good short-term and medium-term tolerance should not be automatically interpreted as proof of safety during continuous use over many years.
- Dedicated human drug-drug interaction studies for NR, NMN, and other NAD+-related compounds remain limited.
- Many clinical trials have excluded participants taking certain drugs instead of directly investigating the risk of interactions, so the lack of reported interactions does not prove that all combinations are safe.
- The oral safety results of NR or NMN cannot be automatically generalized to NAD+ patches, subcutaneous, intramuscular, or intravenous injections, because the routes of administration differ significantly.
- Controlled safety data regarding self-administered subcutaneous or intramuscular NAD+ injections remain limited.
- The IV NAD+ tolerance results discussed in this guide are from a single retrospective real-world study, rather than a randomized comparative trial [8].
- The discussed cancer risk comes from a specific preclinical mouse model and has neither been confirmed nor definitively ruled out in human supplementation studies [9].
- Most NAD+ precursor studies were not designed to evaluate long-term cancer incidence, recurrence, metastasis, or mortality.
- Safety data are insufficient for pregnant or breastfeeding individuals, children, adolescents, and many medically complex populations.
- People with cardiovascular disease, diabetes, cancer, or other chronic conditions may not be adequately represented in general safety studies.
- The composition of the product formulation is another potential source of risk. Adverse reactions may result from inactive ingredients, preservatives, impurities, sterility issues, or formulation differences rather than from NAD+ itself.
- The absence of serious adverse events in a clinical trial does not prove that rare reactions cannot occur in larger populations or with longer exposure.
Disclaimer
The article is for educational purposes only and summarizes scientific research. It does not constitute medical advice, diagnosis, therapeutic recommendations, or a recommendation for the use of NAD+, NAD+ precursors, supplements, patches, injections, or intravenous therapies.
NAD+ and its precursors should not be presented as FDA- or EMA-approved methods for preventing, treating, or curing diseases, unless referring to a specific approved medicinal product and indication.
The article does not contain a full list of possible side effects, contraindications, precautions, allergies, or interactions with medications and supplements.
Available clinical trials provide primarily short- and medium-term safety data and should not be interpreted as confirming the safety of continuous use over many years.
Before starting any supplement or NAD+-related therapy, you should consult a qualified healthcare professional or pharmacist, especially during pregnancy or breastfeeding, in the case of active or past cancer or a significant family history of cancer, cardiovascular disease, or diabetes, as well as when taking prescription drugs or multiple supplements.
In case of chest pain, severe palpitations, difficulty breathing, swelling of the face or throat, symptoms of a severe allergic reaction, increased or persistent vomiting, or other serious or concerning symptoms, seek medical attention immediately.
References
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[2] Dellinger, R. W., Santos, S. R., Morris, M., Evans, M., Alminana, D., Guarente, L., & Marcotulli, E. (2017). Repeat dose NRPT (nicotinamide riboside and pterostilbene) increases NAD+ levels in humans safely and sustainably: A randomized, double-blind, placebo-controlled study. npj Aging and Mechanisms of Disease, 3, 17. https://doi.org/10.1038/s41514-017-0016-9
[3] Fukamizu, Y., Uchida, Y., Shigekawa, A., Sato, T., Kosaka, H., & Sakurai, T. (2022). Safety evaluation of β-nicotinamide mononucleotide oral administration in healthy adult men and women. Scientific Reports, 12, 14442. https://doi.org/10.1038/s41598-022-18272-y
[4] Irie, J., Inagaki, E., Fujita, M., Nakaya, H., Mitsuishi, M., Yamaguchi, S., Yamashita, K., Shigaki, S., Ono, T., Yukioka, H., Okano, H., Nabeshima, Y., Imai, S., & Yasuda, K. (2020). Effect of oral administration of nicotinamide mononucleotide on clinical parameters and nicotinamide metabolite levels in healthy Japanese men. Endocrine Journal, 67(2), 153–160. https://doi.org/10.1507/endocrj.EJ19-0313
[5] Yi, L., Maier, A. B., Tao, R., Lin, Z., Vaidya, A., Pendse, S., Thasma, S., Andhalkar, N., Avhad, G., & Kumbhar, V. (2022). The efficacy and safety of β-nicotinamide mononucleotide (NMN) supplementation in healthy middle-aged adults: A randomized, multicenter, double-blind, placebo-controlled, parallel-group, dose-dependent clinical trial. GeroScience, 45, 29–43. https://doi.org/10.1007/s11357-022-00705-1
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[7] Isman, A., Nyquist, A., Strecker, B., Harinath, G., Lee, V., Zhang, X., & Zalzala, S. (2024). Low-dose naltrexone and NAD+ for the treatment of patients with persistent fatigue symptoms after COVID-19. Brain, Behavior, & Immunity – Health, 36, 100733. https://doi.org/10.1016/j.bbih.2024.100733
[8] Reyna, K., Heinzen, G., Patel, N., Ritter, M., Siojo, A., Legere, H., & Pojednic, R. (2026). Intravenous infusion of nicotinamide adenine dinucleotide (NAD+) versus nicotinamide riboside (NR): A retrospective tolerability pilot study in a real-world setting. Frontiers in Aging, 7, 1652582. https://doi.org/10.3389/fragi.2026.1652582
[9] Maric, T., Bazhin, A., Khodakivskyi, P., Mikhaylov, G., Solodnikova, E., Yevtodiyenko, A., Giordano Attianese, G. M. P., Coukos, G., Irving, M., Joffraud, M., Cantó, C., & Goun, E. (2023). A bioluminescent-based probe for in vivo non-invasive monitoring of nicotinamide riboside uptake reveals a link between metastasis and NAD+ metabolism. Biosensors and Bioelectronics, 222, 114826. https://doi.org/10.1016/j.bios.2022.114826
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