Short answer: Both are forms of vitamin B3. Only niacin (nicotinic acid) causes flushing and changes cholesterol; niacinamide does neither.1 Even so, in two large trials, adding high-dose niacin to a statin did not lower heart events.23 Niacinamide, 500 mg twice a day, cut new non-melanoma skin cancers by 23% in one trial,4 but not in transplant recipients.5
| Niacin (nicotinic acid) | Niacinamide (nicotinamide) | |
|---|---|---|
| What it is | One of the two most common forms of vitamin B3 in supplements; almost completely absorbed1 | The other common form; also almost completely absorbed1 |
| Flushing | Yes, above nutritional needs; extended-release forms are made to reduce it1 | No, because of its slightly different structure1 |
| Cholesterol | Very high doses raise HDL by 10% to 30% and lower LDL1 | No effect; it does not bind the receptors behind niacin's effect on blood fats1 |
| Large outcome trials | AIM-HIGH (3,414 people) and HPS2-THRIVE (25,673 people): no fewer heart events when added to a statin23 | ONTRAC (386 people): 23% fewer new non-melanoma skin cancers in 12 months; ONTRANS (158 transplant recipients): no difference45 |
| Side effects | At high doses: low blood pressure, higher blood sugar, stomach upset, vision problems and liver damage, more likely with extended-release forms1 | Side effects similar to placebo in both skin cancer trials45 |
| NIH upper limit | 35 mg a day of supplemental niacin for adults, unless under medical care; it covers both forms1 | Same limit1 |
NIH says very high doses of nicotinic acid, more than 100 times the daily need, have long been used to treat abnormal blood fats.1 The question was whether that lowers heart attacks and strokes on top of a statin.
In AIM-HIGH, 3,414 people with heart disease took 1,500 to 2,000 mg a day of extended-release niacin or placebo with a statin. HDL rose and triglycerides fell, but the trial stopped early at about 3 years: heart events were 16.4% with niacin and 16.2% with placebo. It was funded by NHLBI and Abbott Laboratories.2 In HPS2-THRIVE, 25,673 people took 2 g of extended-release niacin with laropiprant (an anti-flushing drug) or placebo for a median of 3.9 years. Major vascular events did not drop (13.2% vs 13.7%), and serious problems with diabetes control, infections and bleeding rose. Merck was among the funders.3
In the ONTRAC trial, 386 people who had had at least two non-melanoma skin cancers took 500 mg of nicotinamide twice a day or placebo for 12 months. New skin cancers were 23% lower and precancerous spots (actinic keratoses) fewer, with side effects similar to placebo. The benefit did not last after stopping.4
The same team then tested the same dose in 158 organ transplant recipients. There was no difference: 207 new skin cancers with nicotinamide and 210 with placebo. That trial stopped early because too few people joined.5
They are studied for different things and cannot stand in for each other: niacinamide has no effect on cholesterol, and niacin's cholesterol changes did not prevent heart events in the two large trials. No trial compared the two forms directly. This is general information, not personal advice. More detail: the Niacin (Nicotinic Acid) and Niacinamide (Nicotinamide) guides.