NMN Side Effects: What You Need to Know Before You Start

Any responsible supplement company should be upfront about side effects. Here's an honest assessment of what the clinical data shows about NMN safety — and who should be cautious.

The Good News: NMN Has a Strong Safety Profile

Multiple human clinical trials have assessed NMN safety, and the picture is reassuring. A 2020 safety study found no adverse effects at doses of 100mg, 250mg or 500mg taken orally as a single dose. A 12-week trial at 250mg daily found no significant adverse events. The 2023 multi-dose trial (300mg, 600mg, 900mg) also reported no serious adverse effects at any dose level.

NMN is a naturally occurring molecule — your body already produces it and it's found in small amounts in food. This contributes to its favourable safety profile.

Reported Side Effects

In clinical trials, side effects have been mild and infrequent. The most commonly reported include:

• Nausea: Occasionally reported when taking NMN on an empty stomach at higher doses. Taking it with a small amount of food usually resolves this
• Headache: Rare, usually resolves within the first week as the body adjusts
• Flushing: More commonly associated with high-dose niacin (Vitamin B3); much less common with NMN at standard doses
• Digestive discomfort: Uncommon; again, resolved by taking with food

Who Should Exercise Caution

Cancer patients or those with a history of cancer: NAD+ plays a role in cell proliferation. While NMN doesn't cause cancer, individuals with active cancer or certain cancer histories should discuss NAD+ precursor supplementation with their oncologist before starting.

Pregnant or breastfeeding women: Insufficient safety data exists for this population. Avoid until more data is available.

Those taking prescription medications: NMN may interact with certain medications. Speak to your GP before starting if you're on regular prescription medication.

Under 18: NAD+ levels are naturally high in younger people. Supplementation is not warranted and has not been studied in this age group.

The Bottom Line

For healthy adults over 30 with no contraindications, NMN at standard doses (250–500mg) has an excellent safety record across multiple clinical trials. Start at a lower dose and take it with food if you have a sensitive stomach.

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Written by Dr Chun Tang, MBChB, MRCGP — founder of Little Ox and practising UK GP with 26 years of clinical experience.