What do you mean when you say every cell has a sex? Men and women are different down to the cellular and molecular levels. You either have two X chromosomes, making you a female, or you have an X and a Y, making you a male. That is a fundamental biologic difference that makes men and women different. Those differences are expressed in every organ system.

What kind of differences are you talking about? Women are 70 percent more likely to experience depression over their lifetimes. We also know that there are brain differences between men and women in the areas connected with mood. You can actually see the sex differences when you put men and women in a MRI scanner and you expose them to stressful images. Alzheimer’s is also more common in women, and it’s not just because women live longer. There is a difference in the way that men and women experience the disease. Heart disease is another good example.

You’re hosting a conference in Boston on March 3 on the 20th anniversary of the National Institutes of Health Revitalization Act. How does that law figure in? That law made it mandatory that women and minorities be included in studies funded by the NIH. That was a game changer. Before then, women were not routinely included, nor were minorities.

Are you saying that women are included in the studies now, but the bigger issue of sexual differences is still being ignored? Exactly. Most studies still don’t report outcomes by sex. Sixty-six percent of brain research that begins in animals is either performed in male animals or in animals whose sex is not identified.

There was a 2010 report in the journal Science that said researchers typically use male mice in their experiments because males are cheaper and easier to work with than females. It’s true. It’s true. This sounds so absurd, but it’s really true. This is what is happening today in modern science and medicine.

Do you think it’s happening because most researchers are men? I don’t think we can assume that if we just populate the field with more female investigators it would make a difference. It’s the dominant culture of medicine and science that does not focus on these sex differences and we need to begin to transform the dominant culture.

How do you do that? Will it take a law? Will it take regulations? I’m not sure, but I can tell you it’s got to be more than those of us making the rational arguments. The rational arguments haven’t really turned the tide yet.

You served on a panel assembled by the Institute of Medicine that recommended all forms of contraception be covered under the Affordable Care Act. Why? It’s very clear that the health impact of contraception is extremely positive for women. Being able to space your pregnancies has a very significant impact on the health and well-being of women.

Were you surprised at the sometimes hostile reaction to the panel’s recommendation? The fact that there was such an outcry on birth control is a very unfortunate fact for our country. This isn’t a political hot potato. One of every two pregnancies is unintended. Unintended pregnancy is an epidemic in our country.

Dr. Johnson runs the Connors Center for Women’s Health and Gender Biology at Brigham and Women’s Hospital, chairs the Boston Board of Health, and served on Mayor Marty Walsh’s transition team.