Taking aspirin regularly can reduce the risk of heart attacks in men and strokes in women, according to analysis of six previous studies published in the Journal of the American Medical Association on Jan 17.

For years, many women have taken aspirin on the advice of doctors, based on studies of men, to reduce the risk of heart attack. This report and similar findings from the Women’s Health Study show the drug doesn’t work the same in women as in men.

This is the latest addition to a growing body of evidence on differences between the sexes in the safety and efficacy of medication.

Sex—that is, a person’s biological status as a man or a woman—affects all areas of health. These differences go beyond hormones associated with reproduction and deserve our careful attention.

What are some of the things we have learned about sex differences in medication?

    * For starters, common medications, including antibiotics, antihistamines, antidepressants, antipsychotics, and some heart medications, alone or in combination, cause more women than men to develop a potentially fatal irregular heartbeat.

    * Studies suggest that women may be less responsive than men to anesthesia, the drugs that render a person unconscious during surgery. Women also suffer more side effects from anesthesia, such as headaches and nausea.

The news isn’t all bad for women. Morphine-like painkillers, called kappa opioids, provide more powerful and longer-lasting relief to women than they do to men. At some doses kappa opioids can make the pain worse for men.

Exactly why drugs affect men and women differently remains unclear. The answer may turn out to be different for every class of medication. Nonetheless, research points to several possible mechanisms for these sex-based differences.

The way drugs are broken down in the body may hold part of the answer. Some liver enzymes that process drugs are more active in women than in men, which may affect the levels of drug in the body, drug effectiveness, or the severity of its side effects.

Overall differences in hormonal activity and anatomy affect the way drugs are processed. On average, women have lower body weight, smaller organ size, reduced blood flow, and a higher proportion of fat than men.

Organs seem to function differently depending on whether they are inside a male or female body. Evidence suggests that "female" kidneys are slower to act than "male" kidneys, a difference that may affect how fast the body gets rid of certain drugs.

What does this mean for the specific drugs you take now or may take in the future?

Unfortunately, the Food and Drug Administration, which approves all medications, and the pharmaceutical industry only recently began to analyze how being a woman or man affects the safety and efficacy of drugs. Reporting of this type of information in medical journals, while increasing, is still not routine.

We don’t have a lot of answers about how individual medications affect the sexes differently. The Institute of Medicine, however, made clear in 2001 that research involving both sexes “will have limited value unless the underlying implications—that is, the actual differences between males and females that make such research so critical—are systematically studied and elucidated.”

Without more complete answers, how should we react to emerging evidence about the differential effects of medication on women and men?

Until research verifies sex differences in the effectiveness or safety of a specific drug, you should follow these basic guidelines:

    * Always make sure your pharmacist provides you with information about the drugs you are taking.

    * Ask your pharmacist or doctor if your medication might work differently in women and men.

    * Tell your doctor about everything you take, including prescription and nonprescription drugs and dietary supplements.

    * Drugs may interact with certain foods and beverages, so ask your doctor or pharmacist if you should make any dietary modifications.

    * Let your doctor know about any side effects you may experience and keep track of them when you take your medications.