When it comes to testosterone, women share a few things with men. Like men, they produce the hormone, although in much smaller amounts. Like men, they make less as they get older. And like men, women with low libidos who get testosterone treatments often experience a boost in sexual desire and enjoyment. No wonder millions of American women turn to their doctors to get testosterone prescriptions to enhance their sex lives—even though it’s not FDA-approved for women.

Yet, when it comes to testosterone and libido, women aren’t really like men‑—at all. For women, unlike men, just a little extra “T” can backfire in the bedroom.

Background: “Hypoactive sexual desire disorder” (HSDD)—the medical term for low libido—affects both men and women, but it’s particularly common in postmenopausal women. While there are many factors, including vaginal dryness, that can affect sexual comfort, low levels of testosterone may play a role, too.

Women make small amounts of testosterone in their adrenal glands, ovaries (even after menopause) and in cells with testosterone receptors, but levels start declining in their 20s and are often quite low by the 50s and beyond.

In women with HSDD, testosterone treatment can be an effective treatment, studies show. But there are sometimes side effects, including hair growth, acne and even mood changes.

Study: My colleague and I reviewed existing studies, including animal research, to identify whether women respond to testosterone treatment for HSDD differently from men—and why. One reason the FDA has approved dozens of testosterone products for men but none for women, they suggest, is that the proper dose for each individual woman isn’t understood yet.

Results: Men taking testosterone have a linear dose-related response when it comes to libido. At higher doses of testosterone, men have a bigger increase in libido than they do when taking a smaller dose.

In women, more testosterone may actually mean less desire. Example: 318 postmenopausal women with HSDD were treated with different doses of testosterone or a placebo for 24 weeks. Those who got the lowest daily doses—150 micrograms (mcg)—didn’t have any sexual benefit. Those who got 300 mcg had more sexual desire and more frequent “sexually satisfying” events. But increasing doses up to 450 mcg not only didn’t increase those benefits, it was actually associated with lower levels of desire. Plus, unpleasant side effects were a little higher in these women.

Women, it appears, don’t have a linear response to testosterone treatment—their response is more like a bell curve. You might call it the “Goldilocks effect”—the amount of testosterone that is just right for them.

Surprising finding: To dig deeper into what’s behind this phenomenon, we reviewed animal as well as human studies. One possible reason for the bell curve—while increasing concentrations of testosterone in women increase sexual function, at a certain point the “masculine” effects get in the way. These physical effects include deepening of the voice, hair loss where there should be hair, excessive hair where there shouldn’t be and acne. Not exactly turn-ons. Psychological effects of too much testosterone treatment may also include aggression, anxiety and depression.

Any of these features may affect a woman’s sexual desire and function—and she may become less sexually attractive to her partner. That’s true in animals. Human sexuality is a lot harder to study, we admit, so it’s just a thought experiment for now.

Bottom line: Discuss with your doctor whether this is the best approach for you—depending on your issues, there are many libido-boosting options.

Because there is no FDA-approved testosterone treatment for women, there is no approved dosage, either. If you do decide to be treated using testosterone, work with your doctor, who should be a hormone expert, to determine the dose that seems best for you…and then pay close attention to how the dose you’re taking is affecting you—body and mind. Just a little too much might actually dampen desire. In women, testosterone appears to work best in moderation.