Testosterone Replacement Therapy: A Research-Backed Guide to Diagnosis, Benefits, and Risks

Testosterone replacement therapy is a legitimate treatment for men with clinical hypogonadism. It is also one of the most oversold interventions on the internet, marketed to healthy men in their thirties and forties as a lifestyle upgrade rather than a medical treatment for a defined disease. This article walks through what the mainstream endocrinology guidelines actually say about who is a candidate, how the diagnosis works, what the benefits and risks look like, what the recent cardiovascular safety data show, and where alternatives like clomiphene and hCG fit. It is the medication spoke behind the broader male hormones overview.

Who actually needs TRT: the Endocrine Society definition

The 2018 Endocrine Society Clinical Practice Guideline defines the target population for TRT as men with "unequivocally and consistently low serum total testosterone concentrations" plus symptoms consistent with androgen deficiency. Testing requires morning total testosterone drawn on two separate days, because a single low reading is not diagnostic. The guideline screening threshold is a total testosterone below 300 ng/dL (roughly 10.4 nmol/L), with the typical assay reference range cited as 264 to 916 ng/dL (Bhasin et al., J Clin Endocrinol Metab, 2018).

Symptoms consistent with androgen deficiency include low libido, erectile dysfunction, decreased spontaneous erections, loss of body hair, gynecomastia, small testes, low sperm count, height loss and low-trauma fracture, hot flushes, low energy, and depressed mood. None of these is specific to low testosterone, which is exactly why the guideline insists on both symptoms and confirmed low labs. Treating a "low number" alone is not endorsed by mainstream endocrinology.

Once the diagnosis is made, the workup should include LH and FSH to distinguish primary hypogonadism (testicular failure, high LH/FSH) from secondary hypogonadism (hypothalamic-pituitary problem, low or normal LH/FSH), prolactin (to rule out prolactinoma), SHBG (which changes the interpretation of total T), PSA, hematocrit, and depending on context iron studies and pituitary imaging.

What TRT actually improves

The 2018 guideline summarized the outcome literature in men who meet the diagnostic criteria. The best- established benefits are sexual: sustained improvements in libido, erectile function, and overall sexual satisfaction, though effect sizes are modest (standardized mean differences roughly 0.17 for libido, 0.16 for erectile function, 0.23 for overall sexual satisfaction across pooled trials). T therapy also produces small improvements in mood, and small increases in lean mass and bone mineral density. It does not appear to meaningfully improve "vitality" in men without confirmed hypogonadism, and effects on physical function are modest at best (Bhasin et al., 2018).

The pattern that emerges: TRT is best understood as treatment for a defined deficiency syndrome, not a general-purpose optimization tool. The men who benefit most are the ones who actually meet the diagnostic criteria.

Cardiovascular safety: the TRAVERSE trial

The largest and most-anticipated question for TRT was whether it raised cardiovascular event rates. The TRAVERSE trial (n=5,246 men with hypogonadism and either preexisting cardiovascular disease or high cardiovascular risk) was designed specifically to answer this and reported results in 2023. Testosterone replacement was non-inferior to placebo for major adverse cardiovascular events, with MACE occurring in 7.0% of the testosterone group versus 7.3% of placebo (hazard ratio 0.96, 95% CI 0.78 to 1.17) (Lincoff et al., NEJM, 2023).

The trial did surface a few smaller signals worth knowing. Rates of pulmonary embolism (0.9% vs 0.5%), atrial fibrillation (3.5% vs 2.4%), and acute kidney injury (2.3% vs 1.5%) were higher in the testosterone group. These are not catastrophic effect sizes but they are worth knowing about, especially in men with existing atrial fibrillation risk factors or clotting history. TRAVERSE largely settled the question of whether TRT raises overall cardiovascular event rates in the target population (it does not), while flagging specific mechanisms that deserve monitoring.

Formulations: the tradeoffs

There are several ways to administer testosterone, each with tradeoffs.

Injectable testosterone (typically cypionate or enanthate) is the most common form and provides reliable levels, with dosing every 3 to 7 days for smoother troughs. Peaks and troughs can produce mood and libido fluctuation if dosed weekly rather than more frequently. It is inexpensive.

Transdermal gels and creams deliver a daily dose that mimics diurnal variation but require careful handling to avoid skin transfer to women and children. Absorption varies between men. Patches also exist but are less commonly used because of skin irritation.

Subcutaneous pellets implanted every 3 to 6 months provide steady levels without daily action but require a minor procedure and cannot be quickly adjusted if levels run high.

Oral testosterone undecanoate (Jatenzo, Tlando) is available in the US and avoids first-pass liver toxicity that plagued older oral formulations, but it requires twice-daily dosing with food and is more expensive than injections. Nasal testosterone (Natesto) preserves fertility better than injections but requires multiple daily doses.

Choice of formulation is a decision to make with your prescriber based on your response, lifestyle, fertility goals, and insurance coverage.

Fertility and preserving the HPG axis

Exogenous testosterone signals the hypothalamus that testosterone is abundant, which suppresses GnRH, which suppresses LH and FSH, which suppresses intratesticular testosterone and sperm production. For men who want to preserve fertility, standard TRT is a poor choice. The alternatives are selective estrogen receptor modulators like clomiphene citrate (which raises LH and FSH by blocking estrogen feedback at the hypothalamus, thereby raising endogenous testosterone) and human chorionic gonadotropin (which stimulates the Leydig cells directly and preserves testicular size and sperm production). Both are used off-label for hypogonadism in men who want to preserve fertility, usually under a urologist or endocrinologist familiar with male infertility.

Contraindications

The Endocrine Society guideline lists several conditions where TRT should not be started without first addressing the underlying issue: metastatic prostate cancer or breast cancer, a palpable prostate nodule or induration or PSA greater than 4 ng/mL (or greater than 3 ng/mL in high-risk groups) without urologic workup, hematocrit greater than 50%, untreated severe obstructive sleep apnea, severe untreated lower urinary tract symptoms, uncontrolled heart failure, myocardial infarction or stroke within the last six months, and a desire for near-term fertility (Bhasin et al., 2018). The sleep apnea point is worth pausing on: exogenous testosterone can worsen untreated sleep apnea, and the guideline explicitly advises treating apnea (CPAP or otherwise) before initiating TRT.

Monitoring on therapy

Standard monitoring includes total testosterone at 3 and 6 months and then annually, aiming for the middle of the reference range, and adjusting dose if too high or too low. Hematocrit is checked at baseline, 3 to 6 months, and annually, with treatment discontinued or dose reduced if hematocrit exceeds 54%. Erythrocytosis is one of the more consistent adverse effects, with an absolute risk of about 6% and a relative risk 8.14 times higher than placebo across pooled trials (Bhasin et al., 2018). PSA is checked at baseline and again at 3 to 12 months, with urology referral if PSA rises more than 1.4 ng/mL in twelve months or exceeds 4 ng/mL absolute.

Where TRT fits in the sequence

The strongest version of the male-hormones argument is that TRT is the last lever, not the first. Before considering exogenous testosterone, the higher-leverage steps are almost always the lifestyle drivers covered in what drives testosterone down, the diet interventions in how to increase testosterone naturally with diet and fasting, the training template in resistance training, HIIT, and testosterone, and the deficiency-based supplements in testosterone supplements: what actually works. After those levers have been meaningfully pulled and testosterone remains genuinely low with symptoms, TRT (or fertility-preserving alternatives like clomiphene or hCG) is a reasonable conversation to have with an endocrinologist or urologist familiar with the space.

Disclaimer

This article is for education, not medical advice. Testosterone replacement therapy is a prescription treatment with real benefits and real risks. Do not start, adjust, or stop testosterone therapy without a qualified clinician managing labs and monitoring. Do not source testosterone or ancillary medications outside a licensed pharmacy.