In the episode, which aired last week, Winslet answered questions about a range of topics—including one from an anonymous woman about what she should do about no longer wanting to have sex with her boyfriend after recently putting on weight and feeling unattractive. 

“Sometimes women have a real dip in libido because there might be stuff going on with their thyroid. There could also be stuff going on with your level of testosterone,” Winslet, 48, told the listener.

“A lot of people don’t know this, but women have testosterone in their body, when it runs out—like eggs—it’s gone. And once it’s gone you have to replace it, and that is something that can be done and you’ll feel sexy again. I know,” the Oscar-winner added, seemingly referring to her own use of testosterone replacement therapy (TRT). 

Winslet also suggested that the listener should have her thyroid levels and testosterone levels checked, noting, “Those things could have a direct impact on how you’re feeling. It’s not your fault, our bodies are weird and they behave in strange ways, especially as we get older.”

She continued: “So there could be a dip in those hormonal levels for you that is actually contributing much more than you think to how you feel about having sex with your boyfriend, so I would definitely go ahead and do that.”

Why women need testosterone

Testosterone is a type of androgen, or sex, hormone in everyone’s body, although men’s body’s make more than those of women, who require it at much lower levels, according to the Cleveland Clinic. It’s important for women’s reproductive and sexual health and overall wellness.

But the hormone, produced by women’s ovaries and adrenal glands, begins to gradually decrease beginning in one’s 30s, reaching especially low levels after menopause (although low testosterone can also be caused by estrogen therapy and hypothyroidism). 

While levels of estrogen fluctuate during the menstrual cycle, the hormone is produced consistently until menopause, when it decreases dramatically, causing hot flashes, sleep issues and a host of other problems. Women’s testosterone levels, on the other hand, peak during one’s teens and 20s and go down gradually afterward. 

A blood test given by a doctor can determine whether or not there’s been a drop—which, for women, may mean an impact on muscle and bone health, mood and energy, fertility, and, yes, libido. 

What is Testosterone Replacement Therapy (TRT) for women? 

TRT, or testosterone boosters, are sometimes used for cisgender men who face declining testosterone levels with age. It is also used as a part of gender-affirming care, particularly for transgender men who use the therapy as a masculinizing treatment for gender dysphoria—the psychological distress resulting from an incongruence between one’s sex assigned at birth and one’s gender identity.

But what is TRT for cisgender women? And is Winslet accurate in suggesting it be used for low libido?

Prescribing testosterone—available in forms from pills and injections to creams and patches—may indeed boost sex drive for some women after menopause, according to research: a 2019 meta-analysis which showed that testosterone “significantly increased sexual function” for postmenopausal women, with no serious adverse effects reported, plus a small 2010 placebo-controlled, double-blind study which found that TRT led to “significant improvements” in libido. 

Possible side effects include acne, weight gain, hair loss on head, and an increase in facial hair.

And because there is little research into its safety and long-term efficacy for women, it’s seen as an inappropriate treatment for breast-cancer or uterine-cancer survivors, according to the Mayo Clinic, as well as for women with heart, blood vessel, or liver disease. 

Still, Dr. Arianna Sholes-Douglas, gynecologist and author of The Menopause Myth, says she’s happy to hear TRT get some play. “It’s having its moment. People are talking about it. Hormone therapy is no longer this taboo topic, and there’s not so much fear around it. So that’s good news,” she tells Fortune.

Why is TRT for women controversial?

In addition to the lack of research into its safety, TRT has also not been approved for use in women by the U.S. Food and Drug Administration (FDA)—only in men with low testosterone caused by certain medical reasons. 

Since 2014, in fact, the FDA has been requiring that testosterone therapies come with warning labels that reflect a possible risk of heart attack and stroke. 

Because of the lack of official guidance for TRT for women, doctors sometimes will prescribe to women for an off-label use, which can be “problematic,” notes the Cleveland Clinic, because, “as there isn’t a standard for treatment, providers treat low testosterone in women the same way they’d treat it in men,” despite women requiring a much lower dose. 

Still, off-label use has increased, at least according to one study out of the UK, which found that the number of women in England prescribed testosterone gel increased by around tenfold between 2015 and and 2022—something the study attributes to the airing of a popular menopause documentary series that included information about testosterone treatment for menopausal women with low libido. 

That’s led to some disagreement among physicians.

“Women are being led to believe that it’s the missing piece of the jigsaw, that it’s going to be the solution to their relationship problems, and I think we have to be much more scientific about how that information is provided for women,” Paula Briggs, chair of the British Menopause Society, said in response to the study. “It’s coming from celebrities and politicians, and that’s not necessarily appropriate.”

Sholes-Douglas, meanwhile, is a proponent of prescribing off-label TRT for women—specifically for those dealing with Hypoactive Sexual Desire Disorder (HSDD).

“The biggest concern around it at this point is just making sure that you’re with a provider that understands hormone therapy,” she says. “But I love testosterone. I personally prescribe it a lot of my patients and I think it’s one of the one of the biggest-kept secrets to women, ultimately, feeling good.”

That can be prescribed in one of two ways, she explains: Either with lower dosages of male FDA-approved versions of testosterone, or through what’s called a compounding pharmacy, which mixes and combines ingredients more tailored to the individual patient. Sholes-Douglas offers both options to patients.

The gynecologist adds that she recently attended a Menopause Society meeting, and while it and other similar organizations tend to have strict stances on many aspects of TRT, “In the real world, out here in the trenches, women really do well on testosterone and tend to like it.”

Finally, low libido isn’t always an indication of low testosterone

There may be “more to the story” when it comes to women having low libido, according to Dr. Jolene Brighten, a naturopathic endocrinologist and clinical sexologist who pointed Fortune to a recent article on the topic posted to her website. 

Reasons for decreased sex drive can range from the mental—depression, anxiety, relationship problems, past trauma, or mental illness—to the physical. Those reasons may include use of certain medications (like SSRIs, for depression, nutrient deficiencies, and yes, low hormone production in the ovaries, including estrogen and testosterone.

That’s why, adds Sholes-Douglas, “You really have to dig deep to see: Why is your libido low? Women’s libido is complicated. It’s not just slap some testosterone on and it’ll be better. You need a full workup to see what is really happening.”

If blood tests do indicate low testosterone, for example, it’s important to also have one’s thyroid checked, as hypothyroidism could be a culprit—as Winslet suggested to the podcast listener.

She concluded, though, with this piece of advice: “Go easy on yourself… and if he adores you, let him bloody ravage you.”