Testosterone Formulations Adverse-Event Management Protocols

Which adverse events are most important?

Testosterone products are approved for men with hypogonadism caused by testicular failure or by pituitary or hypothalamic disease; they are not approved for low testosterone due to aging alone [4][7]. The adverse-event list is broad because testosterone affects red cell production, blood pressure, prostate tissue, fluid balance, breast tissue and the pituitary-gonadal axis [4][8].

Hematocrit, blood pressure, prostate cancer risk and lipids are tracked by measurement; VTE and heart failure show up as symptoms. Route changes the size of some signals, especially hematocrit, but the core warnings apply across the class [2][1].

Erythrocytosis: which formulation carries the highest risk?

Erythrocytosis risk differs by formulation, with short-acting injectables showing the highest reported incidence [5]. A 2022 network meta-analysis of 29 placebo-controlled randomized trials in 3,393 men found every testosterone type raised mean hematocrit compared with placebo: intramuscular enanthate or cypionate by 4.0% (95% CI 2.9 to 5.1), oral testosterone undecanoate by 4.3%, gel by 3.0%, patch by 1.4% and intramuscular undecanoate by 1.6% [1].

A 2015 retrospective study of 178 hypogonadal men followed for 3 years found erythrocytosis, defined as hematocrit above 50%, in 66.7% of men on injectable testosterone, 12.8% on gels and 35.1% on pellets [9]. The injection group was younger (mean 42.5 years vs about 54 years) and had a higher baseline hematocrit, and the study was not randomized, so the gap is not a clean route-to-route comparison [9].

Reviews reach the same direction: erythrocytosis risk is well established with testosterone therapy, and short-acting injectable formulations have the highest incidence [5]. One review reported a 315% greater risk of erythrocytosis, defined as hematocrit above 0.52, in men on testosterone replacement compared with controls [10].

The Endocrine Society guideline recommends monitoring hematocrit during the first year of treatment [3]. The Depo-Testosterone label lists polycythemia as an adverse reaction and says to check hemoglobin and hematocrit periodically in long-term use [4]. Studies have used different cutoffs, including hematocrit above 50% and above 52% [9][10].

Blood pressure and cardiovascular events

FDA says ambulatory blood pressure monitoring studies confirmed a blood pressure increase with all testosterone products, class-wide [2]. The Depo-Testosterone label says testosterone can increase blood pressure, that blood pressure should be monitored periodically, especially in men with hypertension, and that testosterone products are not recommended in uncontrolled hypertension [4].

TRAVERSE is the large cardiovascular outcome trial. It randomized 5,246 men aged 45 to 80 with hypogonadism and preexisting or high risk of cardiovascular disease to daily 1.62% testosterone gel or placebo gel [6]. Mean treatment was 21.7 months and mean follow-up was 33 months [6]. The primary MACE endpoint occurred in 7.0% (182) on testosterone and 7.3% (190) on placebo, hazard ratio 0.96 (95% CI 0.78 to 1.17), meeting noninferiority [6].

TRAVERSE tested a topical gel, not an injectable. The FDA review said TRAVERSE did not demonstrate a new safety signal or trend in adverse cardiovascular outcomes [7]. Separately, the Depo-Testosterone and generic enanthate labels still carry older language that long-term cardiovascular safety trials have not been conducted, that studies have been inconclusive for MACE, and that some but not all studies reported an increased risk of MACE [4][8].

Venous thromboembolism is a separate label warning. The Depo-Testosterone label says DVT and PE have been reported with testosterone products and that if VTE is suspected, treatment should be discontinued and workup started [4]. The enanthate label gives the same instruction [8].

Prostate, sleep apnea, edema and other label warnings

The Depo-Testosterone label contraindicates use in men with known or suspected prostate cancer, men with breast cancer, pregnant women and patients with serious cardiac, hepatic or renal disease [4]. The enanthate label contraindicates breast cancer, known or suspected prostate cancer and pregnancy [8]. The Endocrine Society guideline recommends against starting testosterone in men with breast or prostate cancer, elevated hematocrit, untreated severe sleep apnea, uncontrolled heart failure, or myocardial infarction or stroke within 6 months [3].

The Depo-Testosterone label notes that geriatric patients treated with androgens may be at increased risk of prostatic hypertrophy and prostatic carcinoma, although conclusive evidence is lacking [4]. In June 2026 FDA requested further label updates, including revising prostate cancer and benign prostatic hyperplasia safety information [7].

Edema with or without congestive heart failure may be a serious complication in patients with preexisting cardiac, renal or hepatic disease [4][8]. The Depo-Testosterone label also lists hypercalcemia in immobilized patients, hepatic adenomas and peliosis hepatis with prolonged high doses of androgens, gynecomastia that may persist, and injection-site pain and inflammation [4]. The enanthate label lists rare anaphylactoid reactions and injection-site inflammation and pain [8].

Gynecomastia and estradiol

Gynecomastia is listed on the cypionate and enanthate labels and may occasionally persist [4][8]. The mechanism is not testosterone acting directly on breast tissue. Aromatase converts androgens to estrogens, and most gynecomastia results from deficient androgen action or excessive estrogen action in breast tissue; estrogens stimulate breast tissue growth and androgens inhibit it [11][12].

Fertility and spermatogenesis

Exogenous testosterone inhibits pituitary LH and, at large doses, FSH, which suppresses sperm production [4]. The Endocrine Society guideline recommends against starting testosterone in men who plan fertility in the near term [3].

Recovery data are variable. An integrated analysis of 30 studies in 1,549 healthy eugonadal men on androgen or androgen-progestin contraception found a median time of 3.4 months for sperm concentration to recover to 20 million/mL; recovery was 67% within 6 months, 90% within 12 months, 96% within 16 months and 100% within 24 months [13]. Those men were not hypogonadal, so the numbers describe recovery after hormonal contraception rather than recovery in men on testosterone replacement.

In 49 men with azoospermia or severe oligospermia while on exogenous testosterone, treatment with hCG 3,000 units subcutaneously every other day plus clomiphene, tamoxifen, anastrozole or recombinant FSH returned or improved spermatogenesis in 47 (95.9%), with an average time of 4.6 months and mean first density of 22.6 million/mL [14]. In a separate retrospective series of 66 men with infertility after testosterone use, stopping testosterone and giving high-dose hCG plus a selective estrogen receptor modulator led 46 (70%) to a total motile count above 5 million within 12 months; older age and longer testosterone use predicted slower recovery [15].

Lipids and metabolic changes

A 2010 meta-analysis of 51 studies found testosterone treatment raised hemoglobin by a weighted mean difference of 0.80 g/dL and hematocrit by 3.18%, and lowered HDL cholesterol by 0.49 mg/dL (95% CI -0.85 to -0.13) [16]. It found no significant effect on mortality, prostate or cardiovascular outcomes, but the authors described the evidence as low quality with brief follow-up [16].

The authors called the clinical significance of these changes unknown [16]. The enanthate label lists increased serum cholesterol as a metabolic adverse reaction [8].