(MONEY Magazine) – If you have tried -- and tried again -- but still failed to stop smoking, you probably shrugged off the introduction of nicotine skin patches as just the latest wacko ''miracle'' way to kick the habit. But by now, you're probably having second thoughts. After all, one study showed that 26% of smokers who used patches stayed off cigarettes for six months, vs. 12% of placebo-patch wearers. Sales of three existing patches already exceed $300 million, and a fourth, Nicotrol, just hit the market. Before you call your doctor for a prescription, here's what you should know: -- Dr. Robert Shipley, director of Duke University Medical Center's Stop Smoking program, says that there is no discernible difference in the effectiveness of the four patches. All claim to wean you off cigarettes by releasing nicotine into your bloodstream.

-- It takes two to five months to become cigarette-free, assuming the patch works for you. Since patches cost $3 to $4 each, figure on spending $200 to $650. -- Your health insurer probably won't cover the cost unless your doctor prescribes patches to fight a disease such as emphysema. A few cautions: Pregnant women should not use patches, since the nicotine introduced into a woman's system could be harmful to her baby. Two other potential side effects for any user: rashes and sleep problems. You could be part of the 74% who fail, but you will stand a 50% better chance if you take a stop-smoking counseling class at the same time. Local American Lung Association chapters offer a seven-session clinic for $60 to $125. Private groups, such as Smoke Enders and Smoke Stoppers, typically charge between $100 and $325.