Medicine isn't gender neutral: understanding why could make us all healthier.

Consider the classic Hollywood heart attack. First there's left-arm pain, followed by crushing pressure and then a sweating middle-aged man clutching his heart. Yet women in the midst of a heart attack often present none of these symptoms.

"I thought it was either the flu or nausea," says Nancy Loving of her heart attack, which announced itself with back pressure, light-headedness and nausea. Such symptoms, common in women, often result in female heart attack victims being sent home from the emergency room "with a bottle of Tums," says Ms. Loving, Executive Director of WomenHeart: The National Coalition for Women with Heart Disease, based in Washington D.C.

Why the difference? That's a question doctors are now struggling to answer. The big change, however, is that they are asking the question at all. Until recently, the medical world tended to treat women as if they were simply pint-sized men with slightly different plumbing. Research studies almost never included women, so there were no data documenting the differences. In the mid-80s, women started protesting their exclusion, saying the lopsided data made for bad science. About 10 years ago, the government and the medical community recognized the problem and changed the rules for research. The results of subsequent gender-inclusive studies are now transforming the way medicine is practiced.

Indeed, the differences between men and women are turning out to be significant in the diagnosis and treatment of everything from heart disease to depression. "There are sex differences at every level--the cell, the organ, the way the body functions," explains Sally Shaywitz, a neuroscientist and professor of pediatrics at Yale University. For example, we now know there are sex-based differences in both digestive juices and liver enzymes, which explains why men and women often metabolize drugs differently. Men and women also use their brains differently, are susceptible to different diseases and respond differently to treatment. Some diseases even manifest themselves differently. Colon cancers in women, for example, tend to be located higher in the colon. Boys with attention deficit disorder are rowdy, while the girls tend to be quiet.

"One isn't better than the other," says Sherry A. Marts, vice president for scientific affairs at the Society for Women's Health Research, Washington D.C. "Different just means different."

But recognizing those differences means scientists are now able to ask better questions. Why, for example, do women live longer than men? No one has the answer, although the evidence is clear that males have a higher mortality rate all through their lifetimes, says George Lazarus, a New York pediatrician. The result is a lifespan that's, on average, six years shorter than that of women. "Trying to understand the biological reason for some of these things will clearly lead to clinical advances," he says. "It has the potential to lead to better treatment for both sexes."

The Institute of Medicine already has drawn up a list of recommendations for future research on sex-based differences and similarities in a whole host of medical areas, ranging from sex at the cellular level to sex differences in brain function. "It is the way medicine is going to be practiced in the next decade," says Marianne Legato, director of Columbia University's Partnership for Gender-Specific Medicine and author of the book "Eve's Rib." The first medical textbook on the topic, edited by Legato, has just been published, and there is talk that gender-specific medicine may become a specialty medical practice.

Consumers, who played a big role in the initial push to include women in health research, remain a driving force in this fast-evolving field. That's because an educated patient is a potent tool for change in medical practice, Marts says. With information on gender specific medicine increasingly available on the Internet, Marts tells people "Take the issue seriously. Do a little bit of research yourself."

But gender-specific medicine is only the first step, says Sharonne N. Hayes director of the women's heart clinic at the Mayo Clinic, Rochester, Minn. "In 10 years, I think we will be looking beyond gender." By then, she says, more data will be available on other factors like race and ethnicity, and researchers will have dug deeper into molecular medicine. The goal, she says, is individualized medicine.

After all, she says, right now cardiologists, like plumbers, commonly fix a problem by going around it. "What we really want to do is fix it by stopping the disease process."