Males and females of any species are biologically different. There's a growing body of evidence that not only supports that, but also points out that each gender responds differently to certain medical treatments. So why does most medical research mostly only involve male animals and cells in their experiments?

Not only is a new study pointing out the need for including females in medical research, but now, many major medical journals are making it a rule that researchers must indicate the sexes of animals they used in their experiments. Most notably, if researchers only use one sex in a study, the authors of the research must explain why.

Science has already proven that women are medically different from men. Take heart disease, for example, which acts completely different in women. More women die from cardiovascular disease than men, and even the symptoms are often different. Another example is Alzheimer's disease, which is more common in women than men. Women also handle pain differently, and the way they experience that pain is often different.

"Women make up half the population, but in surgical literature, 80 percent of the studies only use males," says Melina R. Kibbe, M.D., senior author of the study. "We need to do better and provide basic research on both sexes to ultimately improve treatments for male and female patients."

The new research, done by Northwestern University, looked at over 2,300 medical studies published in medical journals. Over 20 percent of these studies did not mention the gender of the animals experimented on. Of those studies that did mention sex, a whopping 80 percent only used males.

Women also respond differently to drugs than men and could require different dosages. However, research only done on male animals means that proper dosages for women aren't being examined. Yet these dosages are what's recommended for both men and women, regardless of gender. These wrong dosage amounts could lead to serious medical issues for women.

Interestingly enough, Kibbe was also only using male rats in her vascular research, because male rats don't have hormonal changes, making them easier for studying. However, a fellow researcher opened her eyes.

"I started out with ignorance," says Kibbe. "After Teresa enlightened me, I saw in my own research huge differences between the sexes. I immediately became aware of the significance of this problem."

Laws already cover something similar for human clinical trials, which makes certain that researchers use women in their trials. It's only a matter of time before we see animal research also getting its own set of regulations.

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