From time to time, I've read that some herb teas may be unsafe. Can you give me guidelines for choosing ones that are?

ANSWER - In general, most herb teas likely to cause problems are those sold in bulk, often in health-food stores, with labels that don't clearly define what the mixture contains. On the other hand, prepackaged herb teas manufactured by large companies and found in supermarkets generally are safe if used in moderate amounts. Since some contain mixtures, it's a good idea to read the ingredients list before buying them, if you have allergies.

Among those in the better-left-alone category is lobelia tea, which in high doses can affect respiration and heart rate. The oils in wormwood tea have been reported to cause convulsions, so it, too, is best avoided. Sassafras contains a chemical that has been shown to cause liver cancer in animals. Comfrey also has been found to cause cancer in animal studies. And while chamomile does contain chemicals that relax gastrointestinal muscles (albeit in amounts that even in the strongest teas are too low to relieve symptoms), it can cause serious reactions in those who are allergic to asters, chrysanthemums, ragweed and yarrow.

QUESTION - A good friend has developed irritable bowel syndrome and is experiencing discomfort. I don't want to pester her with questions, but I do want to learn more about the condition. Can you describe it? How common is it?

ANSWER - Hallmarks of the condition are abnormal bowel function and, often, pain. Beyond that, it's hard to make generalizations that apply to all individuals who suffer from the problem. Results of both X-rays and other direct methods of looking at the bowel and "biochemical abnormalities bowel syndrome" (IBS) are inconsistent. Even the name is hard to pin down; it's sometimes referred to as spastic colon or mucous colitis. Symptoms can include indigestion, cramping, abdominal pain and diarrhea, which may alternate with constipation.

Estimating exactly how many people suffer from IBS is difficult for many reasons. Although the condition affects large numbers, the risk is not evenly spread. Using data from several large national surveys, Robert S. Sander, M.D., M.P.H., of the University of North Carolina recently reported in the journal Gastroenterology that as many as 4.7 million Americans - 2.9 percent of the population - suffer from IBS. (The figure came from the National Health and Examination Survey; lower numbers were obtained in other surveys.) And while numbers varied from survey to survey, the trends remained similar.

What are those trends? The condition is over three times more common in women than in men and over five times as likely to be found among whites than among blacks. Rates were highest among those 45 to 64 years old. And it has been estimated to prompt between 20 percent and 30 percent of all referrals to gastroenterology clinics.

QUESTION - I've heard it said that taking a glass of beer or wine before nursing an infant is a good idea because it helps the mother relax. Is there any truth to that?

ANSWER - That's what could be called an old wives' tale - or perhaps just as likely, an old husbands' tale. It's been around for a long time, but that doesn't mean it's true. Actually, drinking could have a negative effect on nursing by inhibiting the so-called let-down reflex necessary for the milk to flow.

And while the concentration is less than that in the mother's blood, even a couple of drinks can cause an infant to become intoxicated. Breast-feeding women should use little or no alcohol.