I know how bad smoking is for your health, but I was surprised to hear recently that it can cause sexual impotence. Is this true or just the latest ploy in the anti-smoking campaign?

A: (From Andrew Weil, MD: An important petition is currently before the federal government, which would require Congress to create mandatory labeling laws for genetically engineered foods. These folks need your support now. To find out more and sign an electronic petition, visit Mothers for Natural Law today. Thank you.)

Yes, as if the all the other damage smoking does to your body weren't enough, add impotence to the list. What's more, the link between smoking and impotence isn't really new. A 1994 study conducted by the New England Research Institute showed that among men with heart disease and hypertension, cigarette smoking was associated with a greater probability of complete impotence. That same year a study by the Centers for Disease Control and Prevention (CDC) found that among 4,462 Vietnam-era vets aged 31 to 49, the prevalence of impotence was 3.7 percent among current smokers compared to 2.2 percent among nonsmokers.

You might also be interested to know that when Pfizer Inc. was testing Viagra prior to FDA approval, three out of four men with erectile dysfunction taking part in the studies were cigarette smokers. Other research indicates that between 39 and 82 percent of men with vascular impotence -- erectile dysfunction stemming from reduced blood flow to the penis -- are smokers. This condition stems from smoke-related damage to the blood vessels supplying the penis. Smoking can also reduce male fertility. Chemical compounds in smoke alter levels of the hormones and enzymes that regulate sperm count as well as the shape and mobility of sperm. As the ads say, " Still think smoking is sexy?" In reality, every puff nudges you closer to impotence and infertility.

This sort of sexual dysfunction isn't limited to men either. During this summer's Viagra craze it became pretty clear that vaginal dryness and other sexual problems in women can result from restricted blood flow to the genitals. That's reason to believe that smoking might not be very sexy for women either. The only thing to do is quit. I know it's not easy. Tobacco, in the form of cigarettes, is the most addictive drug known, and smoking is a most efficient system for delivering nicotine directly to the brain. The only thing to do is to keep at it. If you've tried before and failed, please try again. There is so much help available: acupuncture, hypnotherapy, support groups, nicotine patches and gum. Friday was the Great American Smokeout. I hope you participated, but if not, quit today.

Andrew Weil, M.D.