The nicotinic acid form of vitamin B3, sold both as a vitamin at milligram doses and used as a lipid-modifying drug at gram doses. At those higher doses it produces an intense, harmless-but-alarming skin flush that is its defining characteristic.
Niacin is the most instructive entry in this catalogue, because it does exactly what it claims and it still failed. At 1.5–2 g/day it lowers LDL cholesterol and triglycerides and raises HDL more than almost any other agent — this is not in dispute. Two large randomised trials then tested whether that translated into fewer heart attacks and strokes when added to a statin. AIM-HIGH and HPS2-THRIVE both found no reduction in cardiovascular events, and HPS2-THRIVE found significantly more serious adverse events: new-onset diabetes, infections, bleeding and gastrointestinal problems. Moving a number on a lipid panel and improving health are different things, and niacin is the clearest demonstration of the gap.
Regulation: The Tolerable Upper Intake Level is 35 mg/day for adults from supplements and fortified foods, set on flushing. Gram-level niacin is a prescription lipid-modifying medicine in most countries, yet immediate-release niacin at 500 mg per tablet is sold over the counter as a supplement — a 14-fold gap between the upper limit and freely available single tablets.
What the research used
The amounts, forms and durations published trials of Niacin (nicotinic acid) actually administered.
These are the amounts published trials administered — not a recommendation, and not a dose to copy. Trial participants were screened, supervised and given a characterised preparation. What is in a retail bottle is frequently not what was studied, and the amount that suits one person is not general advice.
Studied for Recommended Dietary Allowance, adults
14–16 mg NE
Strong
14 mg niacin equivalents/day for women and 16 mg for men. Deficiency (pellagra) is now rare outside maize-dependent diets, alcohol dependence and malabsorption.
Studied for Tolerable Upper Intake Level, adults
35 mg
Strong
Applies to supplemental and fortificant niacin, and is based on flushing rather than serious toxicity. Doses used for lipids are 40–60 times this figure and belong under medical supervision.
Studied for Lipid-modifying trials
1500–2000 mg
Strong
Extended-release niacin, daily · 3–4 years
These are the AIM-HIGH and HPS2-THRIVE doses. Both trials found no reduction in cardiovascular events on top of statin therapy, and one found a significant excess of serious adverse events.
This is general information about food, not medical advice. It cannot diagnose, treat or replace guidance from a clinician who knows your history.
When it was taken
Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.
None of the timings below were directly compared in a trial. They reflect how the research happened to dose, or what the pharmacology implies — which is not the same as a timing being better.
🌙Evening
Limited
Lipid doses are conventionally taken at bedtime with a low-fat snack, partly so the flush occurs during sleep. Taking 325 mg of aspirin roughly half an hour beforehand reduces flushing measurably, which has been tested; the bedtime convention itself has not been compared against other times.
Timing was not directly compared. This reflects convention or how the compound behaves in the body, not a trial showing this window works better.
🍽️With food
Limited
Food slows absorption and reduces the intensity of the flush, though a high-fat meal is usually avoided with lipid dosing. Hot drinks, alcohol and spicy food intensify flushing.
Timing was not directly compared. This reflects convention or how the compound behaves in the body, not a trial showing this window works better.
The evidence in depth
Best supported: Moderate
What each association actually rests on, and the papers behind it. A rating describes the state of the research, not how promising the supplement sounds. How we rate evidence.
At gram doses niacin lowers LDL cholesterol and triglycerides and raises HDL cholesterol substantially, reproduced across many trials and meta-analyses. This is the rare case where a supplement moves the marker decisively — and where large outcome trials then showed that moving the marker did not reduce cardiovascular events when added to a statin.
What may be going on: Niacin inhibits hepatic diacylglycerol acyltransferase-2 and reduces VLDL secretion, and acts on the GPR109A receptor in adipose tissue — the same receptor responsible for the flush.
Moderate evidence. Several human studies point the same way, with real caveats.
Two large randomised trials adding niacin to statin therapy found no reduction in heart attacks, strokes or cardiovascular deaths, and one found a significant excess of serious adverse events. Niacin was withdrawn from several guidelines on this basis.
Not enough evidence. Not enough human research to say anything useful yet.
Niacin is a precursor of NAD, which is central to energy metabolism, but there is no evidence that supplementation improves energy or fatigue in people with adequate intake. Pellagra, the deficiency disease, is a different situation entirely.
Not enough evidence. Not enough human research to say anything useful yet.
No source is attached to this association yet, so it is rated not enough evidenceby default. It is listed because people commonly ask about it — not because there is evidence for it.
Things to know
Interactions, contraindications and dose limits, most serious first. Concentrated extracts interact with medication in ways the whole plant does not, so this section carries more weight here than it does on a food page.
Too much
Hepatotoxicity, especially with sustained-release forms
Gram-level niacin can cause liver injury ranging from raised transaminases to fulminant hepatic failure, and sustained-release preparations have been disproportionately implicated because slower absorption favours the hepatotoxic metabolic pathway. Liver function monitoring is standard practice with prescription niacin, and unmonitored over-the-counter use at these doses is the real hazard.
Too much
Trials found no cardiovascular benefit and more adverse events
HPS2-THRIVE reported significant excesses of new-onset diabetes, worsened glycaemic control in existing diabetes, infections, bleeding and gastrointestinal events in the niacin arm, with no reduction in cardiovascular events. Anyone considering niacin for their heart should know that the trials designed to demonstrate that benefit did not find it.
Too much
Raises blood glucose and uric acid
High-dose niacin worsens insulin resistance, can precipitate new-onset diabetes, and raises uric acid enough to trigger gout attacks. Both effects are dose-related and were seen consistently across the large trials.
Interaction
Myopathy risk with statins, and additive effects with blood pressure drugs
Combining niacin with a statin increases the risk of muscle injury, which was one of the concerns in the large trials. Niacin is also vasodilatory, adding to the hypotensive effect of blood pressure medication and alcohol.
Avoid
Avoid in active liver disease, active peptic ulcer and pregnancy at high doses
High-dose niacin is contraindicated in active liver disease and active peptic ulcer disease, and gram doses have not been established as safe in pregnancy. Dietary and RDA-level amounts are a different matter.
Worth knowing
Flushing, and what people do about it
Intense facial and upper-body flushing, warmth, itching and occasionally dizziness begin 15–30 minutes after an immediate-release dose. It is prostaglandin-mediated, harmless, and the main reason people stop. The workaround of buying "flush-free" inositol hexanicotinate is worse than useless — it does not release meaningful nicotinic acid and has no lipid effect.
In the food catalogue
The whole-food form, where one exists. The evidence for a concentrated extract rarely transfers to the food, or the other way round — these are cross-links, not equivalents.