Copyright © 2015, Chicago Tribune

Before a drug or treatment hits the market, it has to be extensively tested. Usually, the test subjects include laboratory animals — mice, rats, pigs. For decades, those critters shared one trait: They were predominantly male. Scientists seeking breakthroughs experimented almost exclusively on male animals. (We'll get to human test subjects in a moment.)

Researchers shunned female animals because they feared the animals' reproductive cycles or hormonal changes could skew the results. Even for diseases prevalent in women, researchers used predominantly male animals in their studies.

The reliance on male animals has carried enormous consequences for women. Drugs that work in men might not work so well in women, or women may report stronger side effects. Women also may require different dosages. In 2013, for example, the U.S. Food and Drug Administration told women to cut in half their doses of the sleeping pill Ambien after research showed that the drug lingered in women's systems.

Of drugs removed from the market by the FDA from 1997 to 2000, 8 in 10 were yanked because they posed greater health risks for women than for men, the U.S. Government Accountability Office reported in 2001.

Now the males-only club is removing its No Girlzz Alowed sign.

A 2014 National Institutes of Health policy that requires scientists to begin using female lab animals takes full effect in January. All basic and animal research must include females — or researchers must justify the exclusion. Bottom line: Use females or lose funding.

This is great news and long overdue.

"I'm really thrilled," says Teresa Woodruff, director of Northwestern University's Women's Health Research Institute, who lobbied for this policy change for years. "I think this is going to be a complete game-changer for science and medicine. If we can get a better understanding of how drugs work at the basic science level, on men and women, that's going to improve the medical pipeline for all of us."

You might think including female animals in research is common sense. But remember, until 1993, many researchers thought nothing of using male subjects almost exclusively in human clinical trials to test a broad array of treatments and drugs. No Girlzz Alowed. As if the physiology of men and of women were so similar as to be nearly indistinguishable.

"The truth of the matter is men and women are very different at the cellular level, at the molecular level, at the systemic level," Doris Taylor, director of regenerative medicine research at the Texas Heart Institute told The Washington Post.

Something you probably didn't know: "Every cell has a sex," Dr. Janine Clayton, director of the NIH's Office of Research on Women's Health, told The New York Times. "Each cell is either male or female, and that genetic difference results in different biochemical processes within those cells. ... If you don't know that and put all of the cells together, you're missing out, and you may also be misinterpreting your data."

In 1993, Congress required that NIH-funded human clinical research studies include women. Today, more than half of the participants in such studies are women. (Even so, the NIH only reports how many women are included in trials, not if researchers are analyzing the outcomes of trials by sex; that would help determine whether males and females are responding differently to the same drugs or treatments.)

The 1993 law also didn't specifically extend to basic research at the animal level. Enter the 2014 NIH policy.

"Most scientists want to do the most powerful experiment to get the most durable, powerful answers," NIH Director Francis Collins told the Times last year. "For most, this has not been on the radar screen as an important issue. What we're trying to do here is raise consciousness."

The best way to do that: with money. The NIH spends billions to drive basic medical research in this country.

When it tells tens of thousands of researchers who rely on NIH grants that they must include females or explain why not, most will be sure to include females. Over time, that should mean treatments and blockbuster drugs that are safer and more effective for all of us.

Copyright © 2015, Chicago Tribune