Before using any NAD+-related product, it is worth understanding what published human safety data actually show. Safety results also vary depending on the route of administration, so oral capsules, transdermal patches, injections, and intravenous infusions should not be treated as if they have an identical adverse 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 generally shown good tolerability in numerous randomised, placebo-controlled human trials.
In an 8-week study of nicotinamide riboside at doses up to 1,000 mg daily, 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 NMN safety studies similarly showed no severe adverse effects with 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. Crucially, some of these symptoms also occurred in participants receiving the placebo with similar frequency, which makes it difficult to determine whether each reported symptom was directly caused by the test compound [1,5].
At the higher tested doses of NR in the Phase I safety study, 3000 mg of nicotinamide riboside per day was administered to people 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 utilising 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 trial data detailing side effects remains limited.
As discussed in our guide on injections, 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 any 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 setting [8].
This is an important route-specific observation.
She 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, as these results came from a retrospective real-world study rather than a randomised controlled trial, they should be regarded 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 for other reasons require greater caution.
Pregnant or breastfeeding individuals were not adequately evaluated in the human NAD+ studies 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 suitably qualified healthcare professional before use.
People with a personal or family history of cancer also require a more individual approach.
As discussed in greater detail in our disease research guide, one preclinical study showed that nicotinamide riboside supplementation was associated with an increased incidence of tumours and brain metastases in a mouse model of triple-negative breast cancer [9].
This result has not been confirmed in humans and came from a specific animal model.
Simultaneously, NAD+ metabolism has a complex relationship with cancer biology, as rapidly dividing tumour 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 cancer-free populations should not be automatically applied to people with active cancer, a history of cancer, or a potentially increased risk of cancer.
Individuals in such situations should discuss NAD+-related supplementation with an oncologist or another appropriately qualified doctor.
Children and young people 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.
Paediatric dosage, safety, impact on development and long-term effects have not been adequately established.
People with certain cardiovascular conditions may also need to exercise greater caution, particularly when considering intravenous or injectable NAD+.
This relates primarily to cardiac symptoms reported in 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 ingredients 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 into drug interactions represents a significant gap in the current NAD+ literature.
Dedicated human studies evaluating the interactions of NAD+ precursors with commonly prescribed prescription drugs are limited.
Many clinical trials have limited the potential for confounding results by excluding participants taking certain medications, rather than purposefully 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.
A certain caution can be deduced from the biological pathways influenced 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.
People using insulin or other glucose-lowering medications should therefore discuss the use of NAD+ precursors with their doctor, particularly 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.
Individuals taking antihypertensive or other cardiovascular medications may therefore benefit from a professional assessment 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 were investigated in specific combinations, but these results should not be automatically generalised to every formulation or every supplement combination.
Claims that two products exhibit a specific „synergistic effect” should therefore be treated with caution, unless the combination in question has been directly tested.
As formal interaction studies remain limited, the most reliable approach is a review of the full list of medicines and supplements by a doctor 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 long-term safety data that is available for medicines or supplements that have been used and studied for many decades.
Within the periods studied so far, the safety results for oral NR and NMN have generally been reassuring.
Many independent research teams have tested various compounds and doses without finding a repeatable pattern of serious adverse events attributed to NR or NMN [1,2,3,4,5,6].
However, a lack of significant safety signals for several 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 in relation to 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 regarding shorter-term use in selected populations, but this should not be confused with actual long-term safety monitoring.
The most precise conclusion is that safety data for short-term and medium-term oral NR and NMN are generally reassuring across multiple human studies, whereas the actual safety of continuous, multi-year use remains insufficiently established.
The cancer issue: what research shows and what it doesn't show
The relationship between NAD+ metabolism and cancer is complex and should not be reduced to claims that NAD+ either „causes cancer” or „prevents cancer”.
Cancer cells frequently 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 reliant 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 specialist imaging method, it was found that nicotinamide riboside supplementation was associated with an increased incidence of tumours and a greater 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 cancer model and a comparable effect has not been demonstrated in humans.
Animal tumour 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 dependence may depend on factors such as cell type, tumour biology, NAD+ metabolism pathways, stage of disease, and potentially the specific precursor or type of intervention studied.
Therefore, individuals with active cancer, a history of cancer, or a strong family history of cancer should 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 evaluate the incidence of cancer, recurrence, metastasis, or long-term oncological outcomes.
When should you stop use and consult a doctor?
A medical evaluation may be indicated if new or persistent symptoms appear 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, particularly if they started after the introduction of a new supplement or therapy.
Chest pain, 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 more frequently reported 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 transient, but increasing pain, swelling, warmth, discharge, spreading 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 are limited, an unexpected symptom cannot always be attributed with certainty to NAD+ alone 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 reaction to occur.
Limitations of current evidence
- Actual long-term human safety data regarding regular supplementation with NAD+ precursors are still not available. Most published studies cover periods ranging from a single dose to a few weeks or months, and some lasted approximately one year [1,2,3,6].
- Good short-term and medium-term tolerance should not automatically be interpreted as evidence of safety with 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 medicines rather than directly investigating the risk of interactions, therefore the absence of reported interactions does not prove that all combinations are safe.
- Oral safety results for NR or NMN cannot be automatically generalised to NAD+ patches, subcutaneous, intramuscular or intravenous injections, as 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 derived from a single retrospective real-world study rather than a randomised controlled trial [8].
- The discussed cancer risks originate from a specific preclinical mouse model and have neither been confirmed nor definitively ruled out in human supplementation studies [9].
- Most NAD+ precursor studies were not designed to assess long-term cancer incidence, recurrence, metastasis, or mortality.
- Safety data are insufficient for pregnant or breastfeeding women, 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 events may stem from inactive ingredients, preservatives, impurities, sterility issues or differences in the formulation, 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 summarises scientific research. It does not constitute medical advice, diagnosis, therapeutic recommendations or a recommendation to use NAD+, NAD+ precursors, supplements, patches, injections or intravenous therapies.
NAD+ and its precursors should not be presented as FDA- or EMA-approved methods for the prevention, treatment or cure of diseases, unless referring to a specific approved medicinal product and indication.
The article does not contain a complete list of possible side effects, contraindications, precautions, allergies, or interactions with medicines and supplements.
Available clinical trials provide mainly data on short-term and medium-term safety and should not be interpreted as confirmation of the safety of continuous use over many years.
Before starting any NAD+ related supplement or 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, with cardiovascular disease or diabetes, as well as when taking prescription medicines or multiple supplements.
In the event of chest pain, severe palpitations, difficulty breathing, swelling of the face or throat, symptoms of a severe allergic reaction, worsening or persistent vomiting, or other serious or concerning symptoms, medical help should be sought 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 randomised, 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 randomised, multicentre, double-blind, placebo-controlled, parallel-group, dose-dependent clinical trial. GeroScience, 45, 29–43. https://doi.org/10.1007/s11357-022-00705-1
[6] Berven, H., Kverneng, S., Sheard, E., Søgnen, M., Af Geijerstam, S. A., Haugarvoll, K., Skeie, G., Dölle, C., & Tzoulis, C. (2023). NR-SAFE: A randomised, double-blind safety trial of high dose nicotinamide riboside in Parkinson’s disease. Nature Communications, 14, 7793. https://doi.org/10.1038/s41467-023-43514-6
[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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