Does niacin (B3) interact with any medications?

The tuberculosis drugs isoniazid and pyrazinamide block the body from making niacin out of tryptophan.

What this means for you

Two different things get called niacin, and only one of them is a vitamin question.

The vitamin interaction is narrow: isoniazid and pyrazinamide, both used against tuberculosis, block the body from making niacin out of tryptophan. Anyone on that treatment is already under close supervision, and this is a point for the treating clinician rather than a reason to buy anything.

It is worth knowing how often that goes wrong, because the answer is more often than you would guess. In 1,212 cases of pellagra published since 2000, isoniazid was the cause in 14.3 per cent, the largest drug-related share of the lot. The figure is probably flattering to the drug's importance, since a case caused by a medicine gets written up more readily than a case caused by poverty. It is still one in seven of the published cases, and it means the connection is real rather than theoretical.

The other niacin is the gram-level dose once prescribed for cholesterol, and the honest summary there is that it failed. Across 23 randomised trials in 39,195 people, nicotinic acid did not reduce deaths, heart attacks or strokes. If you are taking high-dose niacin for your heart on your own initiative, that trial evidence is the reason to raise it with your doctor.

One more combination deserves a mention. If you take gram-level niacin and you also have type 2 diabetes, the two work against each other. Across pooled randomised trials, long-term niacin pushed fasting glucose up by 0.085 mmol/L while it was raising HDL cholesterol by 0.27 and lowering triglycerides by 0.39. The authors of that analysis asked for glucose to be monitored on long-term treatment, which is a sentence to take to whoever manages your diabetes rather than to act on alone.

Flushing at doses above 35 mg is unpleasant rather than dangerous, and it is what the upper limit is based on.

The pairing that is printed on statin labels

Not for everyone. This one is named in FDA-approved statin labelling rather than inferred. Above a gram of niacin a day taken together with atorvastatin, cases of myopathy and rhabdomyolysis, which is muscle breakdown, have been seen. The label tells prescribers to weigh the benefit against that risk. Lipid-lowering doses of niacin are not something to add on top of a statin on your own, and a gram a day is thirty times the supplemental ceiling and about sixty times the requirement.

Two products sold around niacin, both tested

Myth. No-flush niacin gives you the benefit without the flush. The inositol hexanicotinate form was compared head to head with an extended-release niacin, both at 1,500 mg a day. The extended-release form cut total cholesterol by 11 per cent, LDL by 18 and non-HDL by 15, and raised HDL by 12, all clearly significant. The no-flush form moved blood fats no more than placebo and showed no evidence of being absorbed at all. It delivers exactly what its name promises and nothing else.

Myth. NMN and the other NAD boosters restore your metabolism. Pooling every randomised trial of NMN, at 250 to 2,000 mg a day for 14 days to 24 weeks, it came out safe. No increase in adverse events, none in liver enzymes. It also produced no significant change in body weight, body mass index, fasting glucose, HbA1c, blood fats or systolic blood pressure. Safe and inert is the fair summary.

Established. A separate trial shows what that looks like from the inside. Older adults fed 207.5 niacin equivalents a day for a month, as tryptophan, nicotinic acid and nicotinamide together, did change their niacin metabolism: muscle methyl-nicotinamide went from 0.025 to 0.098. Nothing else moved. Mitochondrial respiration, maximally uncoupled respiration and exercise efficiency all came back unchanged. The biochemistry behaved exactly as the theory predicted and the muscle was unaffected.

Written from the evidence cards and the data on this page, then checked back against the sources. Bioma Learn has no human medical reviewer at this time and we say so rather than invent one. Information, not medical advice. How we verify.

Full guide: Niacin: the vitamin that became a heart drug and then failed the trials