Testosterone Replacement Therapy: Pros, Cons, and Risks

The Most Prescribed Hormone in Men's Health

Testosterone prescriptions in the United States tripled between 2001 and 2021, with an estimated 2.3 million men currently receiving testosterone replacement therapy (TRT). The rise tracks with both genuine recognition of testosterone deficiency as a medical condition and aggressive direct-to-consumer marketing from telehealth clinics promoting testosterone as a fountain of youth.

The result is a complicated landscape where legitimate medicine, lifestyle optimization, and pharmaceutical marketing blur together. Understanding what TRT can and cannot do — and the real risks involved — requires separating clinical evidence from marketing claims.

What Is Testosterone Deficiency?

The Endocrine Society defines male hypogonadism as a clinical syndrome resulting from failure of the testes to produce adequate testosterone, diagnosed by consistently low serum testosterone levels (below 300 ng/dL on at least two morning measurements) combined with symptoms.

Symptoms of Low Testosterone

• Reduced libido and erectile dysfunction
• Fatigue and low energy
• Decreased muscle mass and increased body fat
• Depressed mood and irritability
• Decreased bone mineral density
• Cognitive decline (poor concentration, memory)

Who Is Actually Deficient?

The Massachusetts Male Aging Study, a landmark longitudinal study published in the Journal of Clinical Endocrinology & Metabolism (2007), found that testosterone declines by approximately 1-2% per year after age 30. By age 70, approximately 30% of men meet laboratory criteria for hypogonadism.

However, a 2010 study in the New England Journal of Medicine found that only 2% of men aged 40-79 had both low testosterone levels AND symptomatic hypogonadism. The discrepancy matters: many men with low numbers are asymptomatic, and many men with symptoms have testosterone levels within the normal range but are diagnosed and treated based on symptoms alone — a practice with limited evidence.

The Documented Benefits

Sexual Function

The most consistent benefit of TRT. The Testosterone Trials (TTrials), a landmark series of seven randomized placebo-controlled trials published in the New England Journal of Medicine (2016), found that testosterone treatment in men over 65 with low levels significantly improved:

• Sexual desire (moderate effect)
• Erectile function (modest effect)
• Sexual activity frequency (modest effect)

A 2005 meta-analysis in Clinical Endocrinology of 17 RCTs confirmed improvements in libido and erectile function with TRT, though the effect on erectile dysfunction was smaller than that of PDE5 inhibitors (Viagra/Cialis).

Body Composition

TRT consistently shifts body composition toward more lean mass and less fat mass. A 2020 meta-analysis in The Journal of Clinical Endocrinology & Metabolism analyzing 38 RCTs found that testosterone increased lean body mass by an average of 1.6 kg and decreased fat mass by 2.0 kg over 3-12 months.

However, these body composition changes don't always translate to functional improvements. The TTrials found no significant improvement in walking distance (physical function) despite increases in lean mass.

Mood and Energy

The TTrials reported a modest but statistically significant improvement in depressive symptoms with testosterone treatment. A 2019 meta-analysis in Psychoneuroendocrinology found a small-to-moderate effect of TRT on depressive symptoms (standardized mean difference: -0.40), particularly in men with both low testosterone and moderate-to-severe depression.

Bone Density

TRT increases bone mineral density (BMD) in hypogonadal men. The TTrials found significant increases in lumbar spine BMD and estimated bone strength. However, no RCT has demonstrated that TRT reduces fracture risk — the clinically important endpoint.

The Documented Risks

Cardiovascular Concerns

The cardiovascular safety of TRT has been one of the most contentious issues in endocrinology. A 2010 study in the New England Journal of Medicine (the TOM trial) was stopped early due to excess cardiovascular events in the testosterone group among elderly men with mobility limitations.

However, the TRAVERSE trial — the largest cardiovascular safety trial of TRT ever conducted — published in the New England Journal of Medicine in 2023, followed 5,246 men for a median of 33 months and found no increased risk of major adverse cardiovascular events (heart attack, stroke, cardiovascular death) with testosterone compared to placebo.

The current evidence suggests TRT is cardiovascular-neutral for most men, but caution remains warranted in men with established heart failure or recent cardiovascular events.

Erythrocytosis

TRT stimulates erythropoiesis (red blood cell production), increasing hematocrit. A 2017 review in Therapeutic Advances in Urology found that hematocrit rises above 54% (the threshold associated with increased blood viscosity and thrombosis risk) in 5-18% of men on TRT. Regular blood monitoring and dose adjustment (or therapeutic phlebotomy) are essential.

Fertility Suppression

Exogenous testosterone suppresses the hypothalamic-pituitary-gonadal axis, reducing FSH and LH, which dramatically decreases sperm production. A 2019 study in Fertility and Sterility found that TRT reduced sperm counts to azoospermic (zero sperm) levels in approximately 40% of men within 6-12 months. This is often reversible upon discontinuation, but recovery can take 6-18 months, and some men never fully recover. Men desiring future fertility should not take exogenous testosterone.

Prostate Considerations

The historical fear that TRT causes prostate cancer has largely been debunked. A 2016 meta-analysis in Medicine analyzing 22 RCTs found no increased incidence of prostate cancer with TRT. The saturation model, proposed by Abraham Morgentaler and supported by a 2006 study in the New England Journal of Medicine, suggests that prostate tissue becomes saturated with androgens at relatively low levels, and additional testosterone beyond this point does not further stimulate prostate growth.

However, TRT typically increases PSA by 0.3-0.5 ng/mL and may worsen pre-existing lower urinary tract symptoms in men with BPH. Men with untreated prostate cancer should not receive TRT.

Other Risks

• Sleep apnea: TRT may worsen or precipitate obstructive sleep apnea. The Endocrine Society recommends screening for OSA before initiating TRT.
• Acne and oily skin: Common, usually mild, and dose-dependent.
• Testicular atrophy: The testes shrink due to suppressed LH/FSH signaling. Reversible upon discontinuation.

The Monitoring Protocol

Men on TRT require regular monitoring, per the 2018 Endocrine Society guidelines:

• Testosterone levels: Checked 3-6 months after initiation and dose changes
• Hematocrit: Every 6-12 months; dose reduction if above 54%
• PSA: At baseline, 3-6 months, then annually
• Bone density: Baseline DXA in men with osteoporosis risk, repeat at 1-2 years
• Lipid panel: Testosterone can lower HDL cholesterol
• Liver function: For oral testosterone preparations (uncommon in the US)

Before Considering TRT

Lifestyle interventions should be exhausted first, as many are remarkably effective at raising testosterone naturally:

• Sleep optimization: A 2011 study in JAMA found that sleeping 5 hours per night for one week reduced testosterone by 10-15% in young men
• Resistance training: A 2012 meta-analysis in Sports Medicine confirmed that heavy compound exercises acutely raise testosterone
• Body fat reduction: A 2014 study in Clinical Endocrinology found that each unit decrease in BMI was associated with a 2.4 ng/dL increase in total testosterone
• Stress management: Chronic cortisol elevation directly suppresses GnRH and testosterone production

TRT is a legitimate medical treatment for genuinely hypogonadal men that can meaningfully improve quality of life. But it's also a lifelong commitment with real monitoring requirements and side effects, not a casual optimization hack. The decision should be made with a knowledgeable endocrinologist based on repeated lab testing, documented symptoms, and a thorough discussion of risks and alternatives.