NAD+ / NMN

NAD+ (nicotinamide adenine dinucleotide) is a coenzyme every cell needs for energy metabolism and for activating repair-related proteins like sirtuins and PARPs. NAD+ levels are well documented to decline with age, which is the biological rationale behind trying to raise them back up.

Here's the catch that matters for anyone shopping for this: you can't just take NAD+ itself as a pill. NAD+ is a large, charged molecule with poor oral bioavailability, so it's broken down in digestion before it can meaningfully raise cellular NAD+ levels. What's actually sold and studied instead are precursors — smaller molecules the body converts into NAD+ — mainly nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR). When you see "NAD+ supplement" on a label, it is, almost without exception, one of these two precursors, not NAD+ itself.

The biggest, most current picture: a 2026 PRISMA-guided systematic review by Gallagher and Emmanuel et al., published in Ageing Research Reviews, screened peer-reviewed studies from 2010–2025 and identified 113 eligible studies (33 in humans, 80 in rodents) on NAD+-boosting strategies including NR, NMN, and other precursors. Its conclusion is the cleanest summary of where this field actually stands: in humans, oral NR and NMN consistently and reliably raise NAD+-related biomarkers in blood — that part is well replicated — but clinical effectiveness for anti-aging or wellness outcomes remains inconclusive, with the review calling for larger, longer, better-designed trials with prespecified functional endpoints.

Read the systematic review on PubMed →

NMN vs. NR vs. plain nicotinamide, head-to-head: a 2026 randomized, placebo-controlled trial by Christen, Cuenoud, and colleagues (Nestlé Health Science), published in Nature Metabolism, gave 65 healthy adults matched daily doses of nicotinamide (500mg), NR (1,000mg), NMN (1,000mg), or placebo for 14 days. NR and NMN each produced roughly a two-fold increase in whole-blood NAD+ levels, with no significant difference between the two precursors, while plain nicotinamide only produced a short-lived bump. The study also found gut bacteria play a bigger role than expected — converting NMN and NR into nicotinic acid along the way — and that both precursors increased short-chain fatty acid production, a secondary, preliminary finding about gut health rather than a proven benefit in its own right.

Read the trial in Nature Metabolism →

Where the marker-vs-function gap becomes concrete: a 2025 systematic review and meta-analysis by Prokopidis et al., published in the Journal of Cachexia, Sarcopenia and Muscle, pooled randomized controlled trials of NMN and NR against placebo in older adults (mean age over 60) to test whether raising NAD+ actually translates into less age-related muscle loss. It found no statistically significant effect on skeletal muscle index, no improvement in handgrip strength, and no change in gait speed. The authors' own conclusion: "current evidence does not support NMN and NR supplementation for preserving muscle mass and function" in this population.

Read the meta-analysis →

Put together, this is about as clean a "biomarker moves, function doesn't (yet)" story as exists in the supplement world right now: the mechanism is real, the biomarker response is real and replicated across independent labs, but the outcomes people actually care about — strength, physical function, measurable healthspan benefit — have not been shown in the controlled trials run so far.

There is no official or standardized dose for NMN or NR — this is not a nutrient with an RDA, and trials have used a fairly wide range. NMN human trials have most often used 250–300mg/day, with a 2022 safety study (Fukamizu et al., Scientific Reports) testing up to 1,250mg/day for 4 weeks without serious adverse effects. NR trials have generally used higher doses, commonly 300–1,000mg/day. The 2026 head-to-head trial above used 1,000mg/day of either NMN or NR for its 14-day comparison. None of these ranges should be read as a recommendation — they're simply what's been studied, and being honest about it: nobody has established an optimal dose because nobody has established a proven functional benefit to optimize for yet.

Read the NMN safety study →

Regulatory status (US): NMN's legal status as a dietary supplement has been genuinely contested. In November 2022, the FDA concluded NMN did not qualify as a dietary ingredient, reasoning that it had already been authorized for investigation as a new drug (via IND filings tied to a pharmaceutical company's NMN formulation) before being marketed as a supplement. The Natural Products Association filed a citizen petition and a federal lawsuit challenging that reasoning. On September 29, 2025, the FDA reversed its position, concluding NMN is not excluded from the dietary supplement definition after all, and reinstated prior new-dietary-ingredient notifications for NMN products. As of this writing NMN is legally marketable as a dietary supplement in the US again — but the back-and-forth is worth knowing, since it could in principle be revisited again given the unusual history here.

Read about the FDA reversal →

Safety data so far: published human trials, including doses up to 1,250mg/day for NMN over 4 weeks, have generally reported NMN and NR as well-tolerated, with no serious adverse events and only occasional mild complaints like GI discomfort, headache, flushing, or insomnia. That said, the longest published randomized trials run only around 12 weeks, so there's no long-term human safety data yet — a real gap for something increasingly marketed for long-term, ongoing use. Pregnant or breastfeeding people, anyone with a history of cancer (since NAD+ fuels rapidly dividing cells generally, not just healthy ones), and anyone on other medications should talk to a doctor before starting, given how thin the long-term data still is.