Recently, the National Institutes of Health (NIH) took U.S. scientists to task for their gender bias. Published in the journal Nature, an NIH commentary criticized the decades-old practice of omitting female test subjects and tissue samples from medical experiments for new drugs, The New York Times reported.

Previously, the NIH pressed scientists to also test more female subjects in human clinical trials. But many research advocates argue that medical sexism starts way before that stage of research—in fact, it goes back to using mainly male lab animals and tissue samples.

That’s a problem, said the NIH, because a wide swath of studies are now showing that many medications often work far differently in women than they do in men. For example, last year, the FDA told women to cut in half their doses of the sleeping pill Ambien after research showed women metabolized the drug completely differently than men.

The underlying assumption has been that females react to meds no differently than men, said one researcher. But that’s not always the case.

To help stop the research gender bias, starting this October, the NIH will direct scientists seeking federal grants to perform their experiments with both male and female animals. And when handing out cash, grant reviewers will also take into account whether a company’s medical tests are gender balanced.

New research shows that biologically speaking, males might actually be the weaker sex. Click here for more information.