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New Drug Research Must Now Test on Female Animals

To date, nearly all animal trials are done on males only; earlier studies are done on male cell lines.

by Jason Koebler
May 14 2014, 5:47pm
Image: Shutterstock

Time and time again, modern medical research has proven that men and women react differently to certain drugs and are affected by diseases at different frequencies and to different degrees of severity. So why is nearly all preclinical medical research done on male animals and on male cells in test tubes?

The National Institutes of Health announced today that it is developing policies to require all medical researchers that it funds (and there are a lot of them) to use a balance of male and female cells and animals for all future preclinical research. The policies will take effect in October, according to Francis Collins, director of the NIH and Janine Clayton, director of the NIH’s Office of Research on Women’s Health. Exceptions will be made for research that’s specific to only one sex.

The move is similar to one made with the with the NIH Revitalization Act of 1993 that required the inclusion of women (and minorities) in all NIH-funded clinical research, and comes as a result of more proof that testing new drugs on only male mice or primates or cells isn’t going to cut it. 

“The over-reliance on male animals and cells in preclinical research obscures key sex differences that could guide clinical studies,” Clayton and Collins wrote in an article describing the move, published in Nature. “And it might be harmful: Women experience higher rates of adverse drug reactions than men do.”

Among recent findings that spurred the move: Multiple sclerosis affects far more women than men, but women are likely to have less severe symptoms; sex-skewed findings in Parkinson’s, schizophrenia, and stroke research; and the discovery that stress plays a greater role in substance abuse in women than it does in men. 

The move should have probably been a no-brainer, but a disproven fear that menstrual cycles in animals could have an impact on drug research (though, if you think about it, that’s certainly a reason for more equality in preclinical research) and decades-long conventions to test on male animals only have persisted in the industry, according to the NIH. 

Reasons for male focus in animal-model selection centre on concerns about confounding contributions from the oestrous cycle. But for most applications, female mice tested throughout their hormone cycles display no more variability than males do,” Collins and Clayton wrote. Convention is another probable reason for reliance on the male-only models that have been typical in many research areas for decades. Lack of understanding about the potential magnitude of the effect of sex on the outcome being measured is likely to perpetuate this blind spot.”

It’s unclear whether other institutions that fund studies will follow suit, but the move is huge: The NIH spends $30.1 billion annually (not all of that is on medical research, but a huge portion of it is), and doles out 50,000 grants to more than 300,000 researchers each year. The decision has the potential to completely change how preclinical medical research is done.