Why Would a Man Take Testosterone: Uses and Risks

The most common medical reason a man takes testosterone is to treat hypogonadism, a condition in which the body does not produce enough of the hormone on its own. Restoring testosterone to normal levels can improve libido, sexual function, mood, body composition, and bone density.¹ But the reasons men actually end up on testosterone therapy extend well beyond textbook hypogonadism, and the risk profile is more layered than most people realize.

What Hypogonadism Actually Means

Hypogonadism is not just “feeling tired” or “getting older.” It requires both low testosterone on a blood test and symptoms that match, such as low sex drive, erectile problems, fatigue, loss of muscle mass, increased body fat, or depressed mood. A doctor confirming the diagnosis typically orders at least two separate blood draws, because testosterone fluctuates throughout the day. Levels measured before about 10 or 11 a.m. tend to be higher than afternoon levels, particularly in younger men. One study found that men under 30 showed an average drop of roughly 79 ng/dL between morning and afternoon, while older men showed little difference.² Another community-based study found that blood drawn between 8 and 11 a.m. averaged about 412 ng/dL, compared to roughly 368 ng/dL when drawn outside that window.³

This daily rhythm is part of why the diagnosis can be tricky. In younger men, a single afternoon blood draw could make testosterone look artificially low. In older men, the early-morning spike characteristic of youth is often blunted or absent entirely, meaning the time of the draw matters less.⁴ This creates a practical puzzle: a 25-year-old who gets his blood drawn at 3 p.m. might look low on paper but be perfectly fine, while a 65-year-old’s results will be more consistent regardless of the clock.

Age-Related Decline Versus a Clinical Problem

Testosterone does decline with age, gradually and steadily. A large Korean study of nearly 28,000 men aged 40 and older found that levels dropped by about 0.021 ng/mL per year, and the prevalence of biochemical hypogonadism rose from about 5.5% in men in their 40s to roughly 11.6% in men 70 and older.⁵ So age alone does push some men below the clinical threshold, but most men who are aging normally stay within a functional range. The distinction matters because “my testosterone is lower than it was at 25” is not the same thing as “I have a medical condition that warrants treatment.”

Where it gets complicated is that many of the same conditions that drive testosterone down also worsen with age: obesity, poor sleep, chronic stress, and sedentary lifestyles all independently suppress testosterone production. A review of the broader secular decline in testosterone levels pointed to modifiable influences including physical inactivity, unhealthy diets, chronic stress, poor sleep, and exposure to endocrine-disrupting chemicals as substantial contributors.⁶ Research on stress-related testosterone suppression has shown that severe energy deficit, sleep disruption, and uncontrollable psychological stress suppress the hormonal signaling from the brain that drives testosterone production, and that this suppression reverses when energy balance and recovery are restored.⁷ In other words, some men who look like they have low testosterone really have low testosterone because of fixable lifestyle problems, not because their testes have failed.

What Testosterone Therapy Actually Does for the Body

When a man with genuinely low testosterone starts therapy, several things tend to improve. Body composition shifts are among the most consistent findings. In a randomized controlled trial of obese men on a calorie-restricted diet, those receiving testosterone lost about 2.9 kg more fat than those on placebo, and they regained lean mass during the maintenance phase while placebo-treated men did not. By the end of the study, testosterone-treated men had preserved roughly 3.4 kg more lean mass.⁸ A case report tracking a single individual using wearable technology found that lean muscle mass increased by about 6% during an initial phase of testosterone therapy and continued climbing, while body fat dropped, with bigger gains when therapy was combined with regular exercise.⁹

Sexual function is the other area where improvement is well documented. Testosterone therapy consistently improves libido in men with confirmed low levels, though the benefit plateaus once testosterone reaches the normal range. For erectile dysfunction, the picture is more nuanced: testosterone therapy tends to help men with mild erectile problems and can boost the effectiveness of medications like PDE5 inhibitors (the class that includes sildenafil), but it is less useful on its own for severe erectile dysfunction.¹⁰

Mood, Depression, and Cognitive Effects

Depression and low testosterone have a complicated relationship. A meta-analysis of 27 randomized trials involving roughly 1,900 men found that testosterone treatment was associated with a meaningful reduction in depressive symptoms compared to placebo, with the effect being more pronounced at higher doses.¹¹ However, the benefit is not universal. Some subpopulations respond better than others, including men with treatment-resistant depression and those with clearly low testosterone at baseline, while other studies have found no difference between testosterone and placebo on mood outcomes.¹²

Cognition is even murkier. One study found that men who already had cognitive impairment at baseline showed meaningful improvement after eight months of testosterone therapy, while those with normal cognition at the start did not see the same gains.¹³ Testosterone is not a cognitive enhancer for men who are already functioning normally, in other words, but it may help restore function that was lost alongside the hormonal decline.

Metabolic Health and Blood Sugar

There is growing interest in testosterone’s effects on insulin resistance and blood sugar control, especially in men with type 2 diabetes. A meta-analysis of trials in men with both hypogonadism and type 2 diabetes found that testosterone therapy significantly reduced HbA1c, the standard marker for long-term blood sugar control.¹⁴ But the improvements in fasting glucose and fasting insulin were not statistically significant across studies, which suggests the benefit is real but modest in the short run.

Longer-term data paints a more dramatic picture. An 11-year registry study of hypogonadal men with type 2 diabetes found that about a third of those treated with testosterone achieved full remission of their diabetes, and nearly half reached normal glucose regulation over the follow-up period.¹⁵ Registry data is observational rather than controlled, so selection effects could explain some of this. Still, the consistency of the metabolic improvement over a decade of follow-up is hard to ignore, and the underlying biology supports the connection. Animal research has shown that testosterone can reduce the liver’s glucose output through pathways that suppress gluconeogenesis, the process by which the liver manufactures sugar and dumps it into the bloodstream.¹⁶

The Cardiovascular Question

For years, the biggest concern around testosterone therapy was whether it caused heart attacks and strokes. The question got a definitive large-scale trial in the form of the TRAVERSE study, published in the New England Journal of Medicine. In that trial, cardiovascular events occurred in about 7% of men in both the testosterone and placebo groups, and testosterone was formally shown to be noninferior to placebo on the primary cardiovascular endpoint.¹⁷ That same trial did, however, find a higher incidence of atrial fibrillation, acute kidney injury, and pulmonary embolism in the testosterone group, so the overall safety picture is “not catastrophic but not perfectly clean.”

Observational data from U.S. veterans with low testosterone and multiple medical problems also showed no increased cardiovascular risk from testosterone treatment. Transdermal testosterone was actually associated with lower cardiovascular risk in men who already had heart disease.¹⁸ Complicating the picture, a separate large database study found that men on testosterone replacement had a higher risk of major adverse cardiovascular events compared to controls, though the authors acknowledged that whether testosterone itself caused the elevated risk or whether the underlying testosterone deficiency was the real driver remains unclear.¹⁹ The current consensus leans toward testosterone therapy being cardiovascularly safe for most appropriately selected men, but close monitoring remains standard, especially in the first year.

Polycythemia and Thickened Blood

One of the most common side effects of testosterone therapy is polycythemia, a condition where the body makes too many red blood cells, thickening the blood and potentially raising the risk of clots. Roughly 12 to 30% of men on testosterone therapy develop a hematocrit above 51%, compared to about 13% of untreated men, representing roughly a threefold increase in odds.²⁰ The risk is not evenly distributed across delivery methods. A comparison of gels, injections, and pellets found that injectable testosterone was the worst offender, with about two-thirds of men on injections developing elevated hematocrit above 50%, compared to roughly 13% on gels and 35% on pellets.²¹

This is why regular blood work is non-negotiable during testosterone therapy. Doctors typically check hematocrit levels within the first few months and periodically afterward. If levels climb too high, the usual approach is either a dose reduction, a switch in delivery method, or therapeutic blood donation.

Prostate Safety

The fear that testosterone therapy causes prostate cancer was pervasive for decades and traces back to old observations that castration shrank prostate tumors. Modern evidence has not supported the idea that restoring testosterone to normal levels drives cancer growth. In the large TRAVERSE trial, the incidence of high-grade prostate cancer did not differ between testosterone and placebo groups, nor did rates of acute urinary retention, prostate biopsy, or invasive surgical procedures.²²

What does happen is a modest bump in PSA, the blood marker used to screen for prostate issues. In a controlled trial of older hypogonadal men, testosterone treatment raised PSA by an average of about 0.47 ng/mL over 12 months, compared to essentially no change in the placebo group. About 2% of testosterone-treated men crossed the commonly used clinical threshold of a PSA above 4.0, compared to 0.3% of those on placebo.²³ The PSA rise does not appear to reflect cancer risk, but it does mean that men on therapy need to establish a new PSA baseline early in treatment so that any subsequent changes can be interpreted correctly.

The Fertility Trap

Here is something many men do not realize before starting testosterone: it can shut down sperm production. Exogenous testosterone signals to the brain that there is plenty of hormone circulating, so the brain stops sending the signals that tell the testes to make both testosterone and sperm. This is the same principle behind investigational male contraceptives, which use testosterone as the active ingredient.

The effect is reversible, but recovery takes time and is not guaranteed. A study of men trying to restore fertility after testosterone use found that about 70% eventually achieved a usable sperm count with the help of medications designed to restart the hormonal axis. Both age and the duration of testosterone use significantly slowed recovery. The longer a man had been on testosterone and the older he was, the less likely he was to recover sperm production within 6 or 12 months of therapy.²⁴ For any man who wants children in the future, this needs to be part of the conversation before starting treatment, not after.

How Testosterone Is Delivered

Several formulations are available, and the choice involves trade-offs between convenience, blood-level stability, and side-effect profile.

Injections: Testosterone cypionate and enanthate are the most common short-acting forms, with a half-life of about 8 days. They are injected into muscle, usually every one to two weeks. Testosterone undecanoate is a longer-acting injectable with a half-life of about 34 days, requiring less frequent dosing.²⁵ Injections produce peaks and troughs in blood levels, which can cause mood swings and energy fluctuations, and they carry the highest risk of polycythemia.
Gels: Applied daily to the skin, gels provide more stable hormone levels. They reach peak concentration within a few hours and maintain relatively steady levels throughout the day.²⁵ The downside is the risk of skin-to-skin transfer to partners or children, which requires careful hand-washing and covering the application site.
Patches: Worn on the skin, patches deliver testosterone continuously over 24 hours. Skin irritation at the application site is the most common complaint.
Pellets: Implanted under the skin in a minor office procedure, pellets release testosterone slowly over several months. They eliminate the need for daily or weekly dosing but require a small incision and carry a risk of pellet extrusion.

Short-acting formulations like gels and patches mimic the body’s natural rhythm more closely, while long-acting options like pellets and undecanoate injections tend to have better patient adherence but are more likely to push testosterone above the normal range, which can amplify side effects.²⁶

Supraphysiological Doses and Anabolic Steroid Abuse

A significant number of men take testosterone or related compounds not for a medical condition but to build muscle, enhance athletic performance, or improve their appearance. At the doses typically used for these purposes, which can be many times higher than replacement doses, the risk profile changes dramatically. Side effects of anabolic-androgenic steroid abuse include acne, high blood pressure, liver toxicity, unfavorable cholesterol changes, erectile dysfunction, breast tissue growth, and heart muscle damage.²⁷ Suppression of the body’s own hormonal axis, cardiovascular complications, and nervous system damage are also well documented at these levels.²⁸

The distinction between replacement therapy and abuse is enormous. Replacement aims to bring a deficient man’s testosterone into the normal range, typically somewhere between 300 and 1,000 ng/dL. Performance-enhancing use pushes levels far above that ceiling. The side effects that generate fear in the public conversation about testosterone are largely driven by this high-dose, unsupervised use rather than by clinically monitored replacement.

The Telehealth Wild West

The rise of direct-to-consumer men’s health platforms has made testosterone dramatically easier to obtain, but not necessarily safer. An investigation that used a “secret shopper” with completely normal testosterone levels (675 ng/dL, well within the reference range of 264 to 916) found that 6 out of 7 online platforms offered testosterone therapy anyway. Only one platform asked about cardiovascular history or future fertility plans, and most had no testosterone threshold at all for initiating treatment, falling outside both major professional guidelines.²⁹

This creates a real problem. A man with normal hormone levels who starts testosterone will still get the body-composition benefits and the libido boost, at least initially. He will also suppress his own production, making himself dependent on exogenous testosterone for the very functions his body was handling fine before. He will take on the risks of polycythemia, fertility suppression, and everything else discussed above, with none of the medical justification. For men who are genuinely symptomatic and genuinely low, testosterone therapy can be transformative. For men who feel vaguely tired and see an ad on Instagram, the risk-to-benefit calculation is very different.

When Lifestyle Changes Come First

Because so many drivers of low testosterone are modifiable, guidelines generally recommend addressing those before defaulting to hormone replacement. Losing excess weight can substantially raise testosterone on its own. Improving sleep quality and duration matters, since sleep disruption directly suppresses the hormonal signaling that drives testosterone production.⁷ Resistance training in the context of adequate caloric intake does not suppress testosterone and may help maintain levels over time.⁷ Managing chronic stress and reducing exposure to endocrine-disrupting chemicals are also recommended as part of a comprehensive approach.⁶

None of this means testosterone therapy is wrong for men who have done the lifestyle work and still test low. It means that jumping straight to a prescription, especially from a platform that has a financial incentive to prescribe, skips a step that might solve the problem without lifelong medication. A man whose testosterone is 280 ng/dL because he sleeps five hours a night and carries 50 extra pounds has a different problem than a man whose levels are 280 because of pituitary disease, even though the blood test looks the same.

1
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PubMed Central. Testosterone Therapy Improves Erectile Function and Libido in Hypogonadal Men
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JAMA Psychiatry. Association of Testosterone Treatment With Alleviation of Depressive Symptoms in Men
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13
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14
PubMed Central. Treatment with Testosterone Therapy in Type 2 Diabetic Hypogonadal Adult Males: A Systematic Review and Meta-Analysis
15
PubMed Central. Remission of type 2 diabetes following long-term treatment with injectable testosterone undecanoate in patients with hypogonadism and type 2 diabetes
16
PubMed Central. Testosterone supplementation improves glucose homeostasis despite increasing hepatic insulin resistance in male mouse model of type 2 diabetes mellitus
17
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18
PubMed Central. Association Between Testosterone Treatment and Risk of Incident Cardiovascular Events Among US Male Veterans With Low Testosterone Levels and Multiple Medical Comorbidities
19
The Journal of Sexual Medicine. Increased Risk of Major Adverse Cardiovascular Events in Testosterone Deficient Men and in Men Receiving Testosterone Replacement Therapy
20
The Journal of Sexual Medicine. Can Genetics Predict Polycythemia in Patients Taking Testosterone? Use of a Polygenic Risk Score to Predict Polycythemia
21
PubMed Central. Comparison of the Effects of Testosterone Gels, Injections, and Pellets on Serum Hormones, Erythrocytosis, Lipids, and Prostate-Specific Antigen
22
JAMA Network Open. Prostate Safety Events During Testosterone Replacement Therapy in Men With Hypogonadism
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The Journal of Clinical Endocrinology & Metabolism. Prostate-Specific Antigen Levels During Testosterone Treatment of Hypogonadal Older Men
24
PubMed Central. Age and duration of testosterone therapy predict time to return of sperm count after human chorionic gonadotropin therapy
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