Niacin is a natural substance — in fact, it's vitamin B3. Like other vitamins, it keeps the body's metabolism working properly. The Recommended Daily Allowance (RDA) for vitamin B3 is only 18 mg a day. That's far less than the amount needed to improve cholesterol.

In the doses needed to improve cholesterol, niacin is a drug, and a potent one. On average, it can lower LDL ("bad") cholesterol by 10%–25%. Statins and other lipid-lowing drugs do even better, but niacin outshines them all for lowering triglyceride levels (down 20%–50%) and raising HDL ("good") cholesterol levels (up 15%–35%).

Niacin preparations fall into two categories: crystalline and controlled release. Crystalline niacin is quickly absorbed, so it's usually taken two to three times a day. Ideally, you'd take this about 15 to 30 minutes after eating. Typical doses range from 250mg twice a day to 500mg three times a day. Many people have unpleasant itching, flushing (getting a red face), and headaches.

Controlled-release preparations are much less likely to produce flushing and itching. However, they are somewhat more likely to produce liver inflammation, to raise blood sugar levels, and to trigger gout.

Other side effects of any niacin preparation include fatigue, blurred vision, nausea, peptic ulcers, and erectile dysfunction.

Niacin that you buy without a prescription can vary widely in its actual niacin content and potency. Look for one that's USP approved, and once you find a brand and dose that works, stick with it. Avoid the "no-flush" products. They don't cause flushing, but they don't lower cholesterol, either.

Your doctor can prescribe niacin, such as Niaspan. Prescription products have been reviewed by the Food and Drug Administration. They're more expensive, but often covered by insurance. Doctors usually start with a single 500mg tablet at bedtime, then double or triple the bedtime dose if necessary.

Many people turn to niacin because they want to treat themselves. But even though you can get all the niacin you want without a prescription, you should always respect it as a powerful drug. Let your doctor know if you're using niacin. Your doctor who can tell you if niacin is right for you and monitor you to see if it's working and keep an eye out for side effects as you increase the dose.