Yes, aromatase inhibitors increase testosterone levels, often substantially. They work by blocking the enzyme that converts testosterone into estrogen, which triggers a hormonal chain reaction that pushes your body to produce more testosterone on its own. In clinical studies, men taking these medications have seen their testosterone levels double or even triple from baseline within months.
How They Raise Testosterone
Your brain constantly monitors estrogen levels to decide how much testosterone to produce. When estrogen is high, the hypothalamus and pituitary gland dial back their signals to the testes. Aromatase inhibitors interrupt this feedback loop by blocking the enzyme (aromatase) responsible for converting testosterone into estrogen. With estrogen levels dropping, the brain interprets this as a sign that more hormones are needed and ramps up production of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), the two chemical messengers that tell the testes to make more testosterone.
The hormonal shifts are measurable and significant. In one study of subfertile men treated with anastrozole for three months, LH levels roughly doubled, jumping from about 4.0 to 7.4 IU/L in one group and from 3.6 to 11.7 IU/L in another. FSH followed the same pattern. These increases in pituitary signaling directly translated to higher testosterone output from the testes.
This is fundamentally different from testosterone replacement therapy, which introduces testosterone from an outside source and actually shuts down the body’s own production. Aromatase inhibitors preserve natural testosterone manufacturing and, because they boost FSH as well, they also support sperm production. That makes them a relevant option for men who want higher testosterone without compromising fertility.
How Much Testosterone Increases
The degree of testosterone elevation depends on which aromatase inhibitor is used and who’s taking it. A randomized trial comparing the two most common options in pubertal males found stark differences. At one year, the anastrozole group averaged 552 ng/dL while the letrozole group averaged 982 ng/dL, nearly double. Letrozole suppressed estrogen to roughly half the levels seen with anastrozole, which drove the pituitary to push testosterone production harder.
In older men (age 60 and above) with low or borderline testosterone, a year-long trial of anastrozole restored testosterone into the mid-normal range for healthy young men. Men who had the most estrogen-driven suppression at baseline tended to see the biggest gains, which makes intuitive sense: there was more feedback inhibition to remove.
For context, one head-to-head comparison found that clomiphene (a different class of drug that blocks estrogen receptors rather than estrogen production) raised testosterone to 571 ng/dL compared to 408 ng/dL with anastrozole. So while aromatase inhibitors reliably boost testosterone, clomiphene may produce a somewhat larger increase in some men, likely because it blocks estrogen’s effects without actually lowering estrogen levels.
Letrozole vs. Anastrozole
Letrozole is the more potent of the two. In the three-year randomized trial comparing the drugs, estrogen levels on letrozole were half those on anastrozole, and testosterone levels were nearly double. By year two, the letrozole group averaged over 1,000 ng/dL, which sits at the very top of the normal adult male range and sometimes above it.
That extra potency is a double-edged sword. Higher testosterone sounds appealing, but pushing estrogen too low creates its own problems (more on that below). Anastrozole offers a more moderate effect, which is one reason it’s the more commonly prescribed option for managing estrogen in men. A survey of sexual medicine specialists found that 62% chose anastrozole as their first-line medication for elevated estrogen in hypogonadal men, with dosing typically ranging from 1 mg weekly to 1 mg daily depending on the clinical situation.
The Bone Density Tradeoff
Estrogen isn’t just a female hormone. Men need it too, particularly for bone health. When aromatase inhibitors suppress estrogen, bones can pay the price. A one-year placebo-controlled trial in older men found that anastrozole caused a measurable decline in spine bone mineral density. The treatment group lost bone density at the spine (dropping from 1.121 to 1.102 g/cm²) while the placebo group actually gained a small amount. The study’s conclusion was blunt: aromatase inhibition does not improve skeletal health in aging men with low testosterone, even though it successfully restores testosterone to normal levels.
This is the core tension with these drugs. Testosterone went up, but the estrogen suppression that made it possible weakened bones. In younger men or those using lower doses for shorter periods, this tradeoff may be less concerning. But for older men already at risk of osteoporosis, the bone density loss is a real consideration that limits how aggressively and how long these medications can be used.
Effects in Women
The testosterone picture looks quite different in women. Third-generation aromatase inhibitors suppress up to 98% of circulating estrogen in postmenopausal women, and they’re a cornerstone treatment for hormone receptor-positive breast cancer. In women, testosterone can increase modestly because more of it stays unconverted. One small study in premenopausal women found testosterone nearly doubled during letrozole treatment, rising from about 0.86 to 1.64 nmol/L, though this was transient.
The testosterone increases in women are far smaller in absolute terms than in men. Women don’t have the same testicular machinery to ramp up production in response to pituitary signals, so the rise comes mainly from reduced conversion of existing androgens rather than from dramatically increased production.
How They Compare to Other Options
Aromatase inhibitors sit in a middle ground between testosterone replacement and selective estrogen receptor modulators (SERMs) like clomiphene. All three raise testosterone, but through different mechanisms with different consequences.
- Testosterone replacement delivers the highest and most predictable testosterone levels but shuts down natural production and suppresses sperm counts, sometimes to zero.
- Clomiphene blocks estrogen receptors in the brain without lowering actual estrogen levels. This preserves estrogen’s protective effects on bone while still boosting LH, FSH, and testosterone. It tends to produce somewhat higher testosterone levels than anastrozole.
- Aromatase inhibitors boost testosterone while preserving fertility, but they lower estrogen levels throughout the body, which can affect bones, mood, and joint health over time.
The choice between these options often comes down to whether fertility preservation matters and how a man’s body handles changes in estrogen. For men who have genuinely elevated estrogen causing symptoms, an aromatase inhibitor addresses both the estrogen excess and the low testosterone simultaneously. For men whose primary concern is low testosterone with normal estrogen, clomiphene may offer a better balance of benefits and risks.