Why people stop taking NMN

People stop taking NMN for a handful of reasons: they notice no difference, the monthly cost stops feeling justified, they read that the human evidence is thin, they get a side effect, or they lose confidence in the product's legal status. The published trials go a long way to explaining the first of these, because NMN raises NAD+ in the blood fairly reliably while most of the health measures tested alongside it have not changed.

Below, each reason is set against what human studies and regulators have said. Where a reason turns up often in personal accounts but has no data behind it, we describe it and leave it without a number.

The reasons people give for stopping

Published accounts of stopping NMN, many of them on supplement sellers' own blogs, return to the same explanations.

Many start with the complaint that nothing seemed to happen. Someone takes NMN for a few months expecting to feel more energetic or sharper, and feels much the same. That fits the trial data, as the next section shows.

Then there is cost. NMN is sold as a daily supplement with no end date, so it becomes a standing monthly bill, and that bill is harder to justify when the thing it pays for cannot be felt.

Some people stop after reading the research for themselves and finding less in it than they had assumed. Others describe side effects such as headaches, an upset stomach, skin irritation or worse sleep. We have not found a published survey measuring how often NMN users experience these, so we give no figure. The pooled trial data, covered further down, did not find adverse events more common on NMN than in the comparison groups.

The last reason is regulatory. The US regulator changed its position on NMN between 2022 and 2025, NMN has not been authorised as a novel food in Great Britain, and some people stop because they are no longer sure what they are buying.

Does NMN really work?

NMN raises NAD+ in the blood in most trials that have measured it. Whether it changes how a healthy person feels or performs is much less clear, because the results are mixed and the trials are small.

NMN is a precursor. Cells use it to build NAD+, and NMN availability is a rate-limiting factor in how mammals make NAD+. A rise in blood NAD+ is the change NMN produces most consistently in trials, and nobody can feel their blood NAD+ level. The table shows what some of the better-known randomised trials found.

One review pools these trials; another found them too different to pool. The 2026 meta-analysis of 15 randomised trials pooled results from doses of 250mg to 2000mg a day given for between 14 days and 24 weeks, finding no significant effect on body weight, BMI, fasting glucose, HbA1c, blood lipids or systolic blood pressure. Diastolic pressure fell slightly. The 2024 systematic review of ten trials with 437 participants found the trials too heterogeneous to pool; looking at physical performance, it described the improvements it found as non-significant.

Feeling no different after a course of NMN fits this evidence. What the trials detected most reliably was a change in blood chemistry, and the two reviews found no significant improvement in the physical or metabolic measures they looked at, apart from that small fall in diastolic pressure. For the difference between NMN and NAD+ itself, see NMN vs NAD+.

How long does NMN take to work?

Blood levels move within days. In a 14-day trial of 1000mg once or twice a day, blood NAD+ on day 8 was already similar to its day-14 level. In the 60-day trial of 300mg to 900mg, blood NAD+ was up in every NMN group by day 30. In a smaller study, nine men taking 250mg a day saw NAD+ in their white blood cells climb over eight weeks.

Functional measures are another matter. The trials in the 2024 review followed people for 4 to 12 weeks, and the longest NMN trials in the 2026 meta-analysis ran for 24 weeks. Three months of NMN is already as long as any trial in the 2024 review lasted. The trials give no point at which to expect a noticeable change, because they have not reliably shown one.

Is NMN safe?

NMN has been well tolerated in trials, and pooled data show no rise in adverse events compared with control groups. The longest trials ran for 24 weeks, so long-term safety is unknown.

The 2026 meta-analysis drew safety data from ten trials and found NMN did not increase overall, serious or withdrawal-related adverse events, adverse events in any particular body system, or the liver enzymes ALT and AST. Its authors also write that the evidence base "remains dominated by small, short-term trials" and that the safety data cannot exclude rare, delayed or long-term risks. In May 2026 the European Food Safety Authority's nutrition panel concluded that one synthetic form of β-NMN is safe at 300mg a day for adults, excluding pregnant and breastfeeding women. The human trials it reviewed used 250mg to 1250mg a day for 4 to 24 weeks.

Individual trials show how hard it is to pin a symptom on the supplement. In the 14-day Pencina trial, which used a pharmaceutical-grade NMN called MIB-626, one participant on 1000mg twice a day stopped because of diarrhoea, and two had mild rises in liver enzymes: one taking NMN, one taking placebo. In the eight-week Japanese study, mild liver enzyme rises turned up once in the placebo period, once in the washout and once on NMN. The same study measured sleep quality with a standard questionnaire and found no significant change on NMN.

If you are pregnant, breastfeeding, taking prescribed medication or under medical supervision, speak to a doctor before starting or stopping NMN or any other NAD+ product. None of them is for under-18s. The research on NAD+ itself, side effects included, is in NAD+ benefits and side effects.

Where NMN stands with regulators

As of September 2026, NMN does not appear on the Food Standards Agency's register of novel foods authorised for Great Britain. A novel food is one not eaten to a significant degree in the UK or EU before 15 May 1997, and novel foods need to be authorised before they can be placed on the market in Great Britain. The FSA lists an application to authorise β-nicotinamide mononucleotide as in progress, at the risk assessment stage.

In the US, the FDA told one NMN ingredient maker in October 2022 that NMN was excluded from the legal definition of a dietary supplement. In September 2025, answering a citizen petition from the Natural Products Association and the Alliance for Natural Health USA, it changed its interpretation and concluded that NMN is not excluded. A December 2025 FDA letter sets out that sequence and formally sets aside the 2022 letters.

What to weigh before stopping or switching

Start with why you began. If the aim was a higher blood NAD+ level, the trials suggest NMN does that. If it was something specific, such as energy, sleep or weight, it is worth checking whether any trial measured it; for weight, the pooled trials found no significant change, and the one study here that measured sleep quality found none either.

Then think about whether what you noticed, good or bad, came from NMN at all. Placebo groups in these trials produced abnormal blood results too, and in the NR trial described below, both people who dropped out over side effects were taking placebo at the time. A single bad week is weak evidence either way.

If you switch, the alternative will have its own evidence gaps, and the next section covers them. Whatever you move to, it is reasonable to ask the seller for a batch certificate of analysis from an independent laboratory, so you know what is in the product you are comparing.

Other ways people try to raise NAD+

Nicotinamide riboside (NR) is the closest alternative precursor. Nicotinamide riboside chloride is authorised as a novel food in Great Britain for food supplements at up to 300mg a day for adults, with a lower limit in pregnancy and breastfeeding. In a crossover trial where 24 healthy adults aged 55 to 79 completed six weeks on each arm, 1000mg of NR a day raised NAD+ in blood cells by about 60% compared with placebo. A 2023 review of 25 published papers on NR in humans concluded that it has displayed few clinically relevant effects.

The two ordinary forms of vitamin B3, nicotinic acid and nicotinamide, are NAD+ precursors as well. The NHS says taking 17mg or less of nicotinic acid supplements a day, or 500mg or less of nicotinamide, is unlikely to cause any harm, and that high doses of nicotinic acid can cause skin flushes and, over long periods, liver damage.

Direct NAD+ has been studied in people less than NMN has. The human work we know of is on intravenous drips. A 2019 pilot infused 750mg of NAD+ over six hours into eight men and found no change in plasma NAD+ until after two hours, with no adverse events. A 2026 retrospective review of six clinic clients given NAD+ drips recorded moderate to severe digestive symptoms, a raised heart rate and chest pressure during the infusions. Neither study tells you what an injection will do.

We sell NAD+ itself, as a 1000mg pre-mixed vial with a reusable auto-injector, so we have an interest here. We do not claim it will do what NMN did not, and we know of no controlled trial comparing the two. Our science page sets out what NAD+ does in the cell and where the evidence runs out.

Exercise has some human data too. In a 2020 study, 16 untrained middle-aged adults did ten weeks of resistance training, twice a week, and NAD+ measured in their thigh muscle rose by 127%. The study had no comparison group that skipped the training.