Testosterone Replacement Therapy: Benefits, Risks, and Who Qualifies

Testosterone Drops About 1% Per Year After Age 30

Starting in a man's early thirties, testosterone levels decline at roughly 1% annually. By age 70, average total testosterone sits around 40% lower than peak levels in young adulthood. For the estimated 2–4 million American men with clinically low testosterone — a condition called hypogonadism — that decline causes real, measurable symptoms. Testosterone replacement therapy (TRT) exists to correct this deficit, but it's not a lifestyle upgrade available on demand. It's a medical intervention with documented benefits, documented risks, and strict clinical criteria.

What Counts as Low Testosterone

Diagnosis begins with blood work. Most laboratories flag total testosterone below 300 ng/dL as low, though some endocrinology guidelines use 350 ng/dL as the threshold. A single morning draw isn't enough — two separate measurements on different days are required because testosterone fluctuates significantly by hour and day. Free testosterone (the biologically active fraction) matters too, especially in men with obesity or elevated sex hormone-binding globulin (SHBG) that "ties up" circulating testosterone.

Primary vs. Secondary Hypogonadism

Primary hypogonadism means the testes themselves are failing — from injury, chemotherapy, Klinefelter syndrome, or autoimmune damage. Secondary hypogonadism points to the pituitary or hypothalamus: insufficient LH and FSH signals never reach the testes. The distinction matters clinically. Men with secondary hypogonadism who want to preserve fertility are often better served by gonadotropin therapy (hCG, FSH injections) than by exogenous testosterone, which suppresses the body's own LH/FSH production.

Delivery Methods Compared

TRT is not a single product. It comes in several forms with meaningfully different pharmacokinetics, cost profiles, and side effect risks.

Method	Dosing Frequency	Pros	Cons
Intramuscular injection (cypionate/enanthate)	Every 1–2 weeks	Low cost, reliable levels	Peaks and troughs, injections required
Subcutaneous injection	Twice weekly	Smoother levels, easy self-administration	Still requires injections
Topical gel/cream	Daily	Non-invasive, stable levels	Transfer risk to partners/children
Transdermal patch	Daily	Steady delivery, no transfer	Skin irritation common
Buccal tablet	Twice daily	No skin contact issues	Gum irritation, less popular
Pellet implant	Every 3–6 months	No daily compliance needed	Minor surgical procedure, hard to reverse

Evidence-Backed Benefits

The Testosterone Trials (TTrials) — a landmark NIH-funded set of seven coordinated studies published from 2016 to 2018 — provided the most rigorous evidence to date. They enrolled 790 men over 65 with confirmed low testosterone and tracked outcomes over 12 months.

Sexual function: Significant improvement in libido, erectile function, and sexual activity versus placebo
Physical performance: Increased walking distance, grip strength, and lean muscle mass
Bone density: Volumetric bone mineral density increased substantially at the spine and hip
Mood and energy: Modest but statistically significant improvements in depressive symptoms and self-reported vitality
Cognitive function: No significant benefit found in the memory or cognitive subtrials

Outside the TTrials, consistent evidence supports TRT for men with diabetes or metabolic syndrome: improvements in insulin sensitivity, fasting glucose, and waist circumference are reproducible across multiple meta-analyses.

Risks That Demand Informed Consent

TRT is not without meaningful risks, and several are dose-dependent.

Risk	Mechanism	Mitigation
Erythrocytosis (high RBC/hematocrit)	Testosterone stimulates erythropoietin	Monitor hematocrit; dose-adjust or phlebotomize
Infertility/testicular atrophy	Suppresses LH/FSH, halts spermatogenesis	Add hCG; stop TRT if fertility desired
Acne and oily skin	Androgen receptor activation in sebaceous glands	Topical treatments; adjust dose
Sleep apnea worsening	Upper airway muscle changes	Screen before starting; CPAP if needed
Gynecomastia	Aromatization to estradiol	Aromatase inhibitors if severe
Prostate growth	Androgen-sensitive tissue	PSA monitoring; contraindicated in prostate cancer

The Cardiovascular Question

The cardiovascular safety of TRT has been genuinely contested. A 2010 study in the New England Journal of Medicine was halted early due to excess cardiovascular events in the TRT arm. Later, the 2023 TRAVERSE trial — the largest cardiovascular safety study of TRT, enrolling over 5,200 men — found no statistically significant increase in major adverse cardiac events versus placebo over a median 33 months. However, TRT did increase pulmonary embolism and atrial fibrillation rates, reinforcing the need for careful patient selection.

Who Should Not Use TRT

Absolute contraindications include active or suspected prostate cancer, male breast cancer, severe untreated obstructive sleep apnea, and polycythemia. Men seeking fertility should be counseled on alternatives before starting TRT, since spermatogenesis suppression can take 6–12 months to reverse after stopping — and in some cases does not fully recover.

Monitoring Protocol

Clinical guidelines from the American Urological Association and Endocrine Society recommend baseline PSA, hematocrit, and total testosterone before starting, then follow-up labs at 3–6 months and annually thereafter. The goal is typically to maintain total testosterone in the mid-normal physiologic range (400–700 ng/dL) — not to supraphysiologic levels used in non-medical contexts.

This article is for informational purposes only. Consult a qualified healthcare professional before making medical decisions.