Testosterone for Women: What It Actually Does to Your Brain

"You know that scene from The Wizard of Oz where it goes from black and white to technicolor? That's my brain on testosterone."

That's a patient of Dr. Kelly Casperson's, speaking about starting testosterone therapy.

Then Casperson herself, at the same event:

"Picture 108 million women energized, focused, and ambitious. Not in spite of their age, but because they are supported through it."

These two sentences were said in a federal hearing room, to the FDA Commissioner of the United States, by a board-certified urologist who has spent her career watching women's quality of life collapse from something treatable, and then watching those women be told nothing was wrong.

This hearing, on July 17, 2025, was officially about removing the black box warnings from hormone therapy products. But tucked inside it was something else, a reckoning about testosterone, and how completely medicine has failed women on this one.

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This is not just a libido hormone

The first thing to dismantle is the stereotype. When most people hear "testosterone for women," they assume the conversation is about sex drive. That's a half-truth that has done a lot of damage.

Here's what Casperson actually told the FDA panel:

"Testosterone stereotype is that it's just for libido. It's a half-truth. It's a neurohormone critical for mitochondria, nerve function, muscle, bone, and brain function. Libido improves because dopamine and blood flow in the brain improve."

Libido improves as a downstream consequence of the brain working better, not because testosterone is some aphrodisiac switch. The brain has testosterone receptors throughout. When testosterone is restored to physiologic levels, dopamine signaling improves, blood flow improves, mitochondrial function improves, and the whole system runs more efficiently. Better sex drive is a side effect of better brain function.

Here's what testosterone actually does in the female body:

In your brain: It's a neurohormone that supports dopamine production, nerve conduction velocity, and cerebral blood flow. It drives what researchers call "goal-oriented behavior", the ambition, focus, and motivation to pursue things. Women who are deficient don't just feel tired; they feel flat. Uncaring about things they used to care about.

In your bones: Testosterone directly stimulates osteoblasts, the cells responsible for building new bone. This is distinct from estrogen's role in protecting existing bone. You need both.

In your muscles: Testosterone drives muscle protein synthesis and recovery. It's why resistance training yields results more slowly in perimenopause. The anabolic signal that supports repair is declining.

In your mitochondria: This is the cellular energy piece. Testosterone is involved in mitochondrial biogenesis, the production of new mitochondria. Less testosterone, less efficient energy production at the cellular level. This is why the fatigue that comes with deficiency doesn't respond to more sleep.

You make more testosterone than estrogen by mass. Not a little testosterone. Several times more, and after menopause fifteen times or more, because estradiol falls away and testosterone doesn't. It isn't a trace hormone that barely registers. It's foundational to your baseline biochemistry, and it starts declining around age 25: roughly half by age 40, and another quarter or so between your early forties and your late fifties. Before the hot flashes start. Before the cycle irregularities begin. Before anything announces itself as menopause.

And what that does to your brain, specifically, is about dopamine.

I covered the full neuroscience of this in Part 1, My Antidepressant Couldn't Fix This. Testosterone Did., including the VTA, the mesolimbic pathway, tyrosine hydroxylase, and anhedonia as a dopamine-system problem. If you haven't read it, start there; the brain science is the foundation for everything that follows.

The short version for context: testosterone acts directly at the origin point of the brain's two major dopamine pathways. Both carry androgen receptors at the VTA. Testosterone supports dopamine synthesis, receptor density, and reward-circuit function. When it declines, the system that generates motivation, pleasure, and the desire to pursue things runs at reduced capacity. This is why the clinical presentation of testosterone deficiency and anhedonia overlap so heavily, they share the same underlying mechanism.

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A regulatory failure, plainly named

There are zero FDA-approved testosterone products for women in the United States, at any dose, for any indication. There are 68 for men, 47 of them generics, which is what a solved problem looks like.

That isn't because it was never tried. Five estrogen-and-testosterone injectables were approved here, prescribed for roughly sixty years, and withdrawn, and the same drug class is still sold in Mexico, Japan, Peru and Taiwan. The reason nobody has been back to the FDA since 2004 turns out to be about patents rather than about safety. The whole history, including the twelve words that did more damage than any study: why there's no FDA-approved testosterone for women.

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Why the research missed it

You will be told the evidence doesn't support this. That's true about the literature and misleading about the hormone. The trials measured testosterone with an assay that can't reliably read female concentrations, most ran twelve weeks against a consensus that says give it six months, and almost all of them asked only about sexual function. The full case, including the CDC study where one woman's blood came back as anything from 7.1 to 39.8 ng/dL depending on the lab, is here: why testosterone studies in women keep finding nothing.

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The side effects you deserve to know about

Clitoromegaly, voice deepening and hair loss are the three that get used to frighten women off this therapy, and the global consensus found no association with any of them at female doses. The safety evidence that answers the fear comes from a population almost nobody thinks to look at. That's a long enough subject to deserve its own page, and it has one: testosterone side effects in women, and what's really just too high a dose.

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My own experience, the honest version

Here is what I can tell you from the inside.

Before testosterone, I had textbook anhedonia. Didn't want to get out of bed in the morning. Couldn't summon the pull toward things I used to care about. This is worth naming precisely: I've been on an antidepressant for 30 years. It was doing its job on the serotonin side of things. But SSRIs and SNRIs address serotonin pathways, not the dopamine-mediated anhedonia that comes from testosterone deficiency. Those are different systems. Someone can be "treated" for depression and still experience the flat, motivationless quality of testosterone-deficiency anhedonia, because the antidepressant isn't touching that pathway at all. That's exactly what was happening to me.

On testosterone, I wake up actually wanting to get out of bed. Not in a "I should get up" way, but in the way I felt at 30, when the day felt like it held something worth getting to. I have the drive to finish things I start, which is different from discipline. Discipline is pushing yourself. This is pull. The creativity that built adoption.com from nothing in 1995, the kind that has you thinking about a new business at 7am before coffee, genuinely excited about the problem, came back. Hard things started feeling worth doing again rather than optional. At the gym, I'm not negotiating with myself to get through it; I want to be there. That quality of wanting is what I had lost, and I hadn't realized how much it shaped the texture of a day until it returned.

The neuroscience explains this exactly. Testosterone is a neurohormone that supports dopamine signaling and blood flow in the brain. What Casperson said at the FDA hearing about libido improving "because dopamine and blood flow in the brain improve", I felt that before I understood the mechanism. The goal-directed behavior researchers measure in studies, the ambition and motivation to pursue things, isn't vague. It's the literal experience of waking up with somewhere you want to go. The cellular energy piece connects too: testosterone is involved in mitochondrial production. Less testosterone means less efficient energy generation at the cellular level, and that explains why the fatigue that goes with deficiency doesn't fix with more sleep. I have been both versions of myself. The difference is not subtle.

I can tell you all of this with confidence because I can feel the cycle. My current dosing makes that unavoidably clear. I started exploring testosterone in London as a patient at Newson Health, Louise Newson's clinic. They prescribed AndroFeme, a testosterone cream originally developed in Australia and prescribed through Newson Health. Follow-up blood tests showed insufficient absorption, my working theory is that it was related to being overweight at the time, since skin thickness and body composition genuinely affect how much of a topical crosses into circulation. I felt nothing.

I moved to injectable. I've been using Despamen, a combination injectable available over the counter at Mexican pharmacies, testosterone enanthate 100mg plus estradiol valerate 5mg in one pre-filled syringe.

And when it works, it works the way I described above. All of it.

Here is the problem: testosterone enanthate has a half-life of about 4.5 days. The label says once a month. Injected on that schedule, levels peak in the first days and fall through subtherapeutic ranges by weeks two and three, which leaves roughly ten to fourteen days with essentially no hormone on board before the next dose. I could feel that window close. The drive went quiet. The excitement in the morning flattened out. Everything that hinges on the injection became visible precisely because it disappeared on a predictable schedule, and what came back in that gap was the anhedonia.

So I take it twice a month instead.

I want to be straightforward about what that means rather than let it sit in the small print. 100 mg of testosterone enanthate is a male replacement dose, and taking it twice a month puts me above the physiologic range for a woman. I know that. I am knowingly taking a supraphysiologic dose. The 2019 international consensus on testosterone therapy for women bases its safety conclusions on doses that approximate premenopausal female concentrations, and I am not in that range. Every reassuring thing that consensus says about side effects is conditioned on a dose I am not taking.

I made that trade with my eyes open, because the alternative on offer was two weeks a month of the thing I started treatment to escape. That is my decision about my own body, made with information. It is not a recommendation, and it is emphatically not a protocol to copy.

The fact that I can feel the cycle at all is still useful information. It means the hormone is doing something real when it's present, and it means the monthly schedule was built for convenience rather than for anyone's physiology. What I actually want is the opposite of a big infrequent dose: smaller amounts more often, twice weekly or every other day, holding a steady level instead of a spike followed by a decline. That would let me come down in total exposure while feeling better, not worse. It is the thing I am working on.

If you take nothing else from this section: I am not the model. I am a woman solving for herself, in a country where the product exists over the counter, because the country I'm from never approved one. A clinician dosing you from scratch would almost certainly start somewhere very different, and should.

This is not a perfect story. I'm still figuring out what works for me. Which is, I think, the honest experience for most women navigating this without the FDA having done the regulatory work to make it straightforward.

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Your delivery options, an honest assessment

Since no FDA-approved product exists for women, you're working in the world of off-label and compounded. Here's what the options look like:

Topical cream or gel is where most specialists start. Applied daily to a consistent site, inner wrist, inner thigh, upper arm. Absorption varies significantly by individual; skin thickness, body composition, and application site all affect how much actually crosses into circulation. For women who absorb well, it's the gentlest entry point with the easiest titration. You can adjust dose quickly. For women who don't absorb well (like me), it produces good labs for some and nothing for others.

Subcutaneous injection is the option most intimidating to women who haven't considered it, and the one most likely to change their minds once they understand the needle. We're talking about a 27 to 31 gauge needle, half an inch long, going into belly fat or thigh fat. A 2017 study published in the Journal of Clinical Endocrinology & Metabolism by Spratt and colleagues confirmed that subcutaneous testosterone achieves therapeutic levels effectively, with patients strongly preferring it over intramuscular injection for comfort and convenience.

If you've ever injected Ozempic, Wegovy, or Mounjaro, you've already done this. The GLP-1 pen needles are 31 to 32 gauge, 4 to 6 millimeters long. Subcutaneous testosterone uses a 27 to 31 gauge needle, about 12 to 16 millimeters. They're in the same category. If you've pulled off a weekly Ozempic shot, the "I can't inject myself" belief doesn't survive the comparison. The skill set is identical.

Weekly or twice-weekly small subcutaneous injections also solve the pharmacokinetics problem, you maintain stable, steady levels rather than the spike-and-crash cycle that monthly injections guarantee.

Pellets, inserted under the skin every three to six months, are heavily promoted at hormone clinics and are the one I'd push back on hardest as a starting point. Kelly Casperson puts it well: "Pellets tend to run supraphysiologic and that means hair loss and side effects. You need to earn your pellet. Don't go from zero to Mount Everest." The practical problem is irreversibility. You cannot take a pellet out if the dose is wrong, you wait months for it to dissolve, and ACOG recommends against them as first-line therapy. My guidance: use a removable form first, establish that you respond well and aren't prone to side effects, then revisit pellets as a convenience option. There's also a risk that rarely comes up in the sales pitch: testosterone pellets and endometrial risk.

The complete side effects discussion, including clitoromegaly, voice deepening, and the hair loss question with its management options, has its own page: testosterone side effects in women.

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If you think you might be deficient

The symptom picture for low testosterone in women overlaps heavily with perimenopause: fatigue that sleep doesn't fix, brain fog, low libido, difficulty building muscle despite consistent effort, low motivation, mood flatness, a reduced sense of ambition or competitive drive. If you're in the 40-to-65 range and have several of these, it's worth investigating.

The right labs: total testosterone, free testosterone by equilibrium dialysis, and SHBG. Tested together. Morning draw. Also useful: DHEA-S, estradiol, and FSH to see the full picture.

Find a menopause specialist rather than a general practitioner. The North American Menopause Society has a provider finder at nams.org. You are asking for off-label treatment, there is no FDA-approved product, so you need a doctor who knows how to navigate that landscape. A GP who hasn't been trained in this territory may be unfamiliar with what's available or uncomfortable prescribing it; a menopause specialist won't be.

If you're currently taking an oral contraceptive, ask specifically for free testosterone and SHBG, not just total testosterone. That's a conversation most doctors aren't initiating. You may need to start it.

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Back to the Wizard of Oz

That patient's brain going from black and white to technicolor has a mechanism. Mitochondria, dopamine, and a neurohormone her body stopped making in adequate quantities. When it was restored, her brain came back online. The cognitive flatness, the fatigue, the sense of operating at partial capacity, those are symptoms with a mechanism, not the normal price of getting older.

108 million women. Energized, focused, ambitious. Not in spite of their age, but because they are supported through it.

It took until 2025 for anyone in a federal hearing room to say that out loud and mean it.

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Annette Thompson is 57, the founder of adoption.com, and a menopause advocate writing about evidence-based women's health.

This article is educational and does not constitute medical advice. Talk to a physician before starting any hormone therapy.

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Sources

The therapy works, and the safety data exists - Islam RM et al., Lancet Diabetes and Endocrinology 2019, the definitive meta-analysis of randomized trials: testosterone reliably improves sexual function in women. It also found the evidence on mood, cognition, and musculoskeletal outcomes was still insufficient, which is exactly the gap this article is about. - Davis SR et al., Journal of Sexual Medicine 2019, the Global Consensus Position Statement on Testosterone Therapy for Women, published simultaneously in several journals: the international standard-of-care document. - Achilli C et al., Fertility and Sterility 2017: transdermal testosterone improves hypoactive sexual desire disorder in postmenopausal women. - Davis SR and Wahlin-Jacobson S, Lancet Diabetes and Endocrinology 2015: the physiology review behind testosterone as a neurohormone and its decline with age.

The age-related decline - Zumoff B et al., J Clin Endocrinol Metab 1995: the source of the "about half by 40" figure. An expected 0.61 nmol/L at 40 against 1.3 nmol/L at 21, read off a fitted regression in 33 healthy cycling women, so treat it as a well-replicated shape rather than a precise measurement. - Wang Y, Islam RM, Bond M, Davis SR, eBioMedicine 2025, the Australian Women's Midlife Years (AMY) study, 1,104 women aged 40 to 69 measured by mass spectrometry: the source of the further quarter. Median testosterone fell from 0.56 nmol/L at ages 40 to 44 to 0.42 nmol/L at 55 to 59, reaching a nadir at 58 to 59 before rising modestly, with no effect of natural menopause itself. - Davison SL et al., J Clin Endocrinol Metab 2005, n=1,423: androgens decline continuously with age, with no menopause step-change. Cited for that shape only; it does not contain the "another quarter" figure.

Beyond libido - Horwath O et al., Journal of Applied Physiology 2020: testosterone drives measurable muscle fiber growth in women (a randomized trial in young women).

Delivery - Spratt DI et al., J Clin Endocrinol Metab 2017: subcutaneous testosterone reaches therapeutic levels and patients prefer it to intramuscular injection.

The trans men safety cohorts (de Blok 2019, the 2026 Frontiers review) and the hair-loss drug trials (Verdonschot 2014, Nascimento e Silva 2022, Vano-Galvan 2021) now sit with the claims they support, on testosterone side effects in women.

The 56% anhedonia cohort (Glynne 2024) now sits with the argument it supports, on why testosterone studies in women keep finding nothing. The TRAVERSE trial and the FDA regulatory record sit with the history.