Testim Side Effects: What to Expect and When to Call Your Doctor

Like all medications, Testim (testosterone 1% gel) can cause side effects. Most are mild and manageable, but some are serious and require immediate medical attention. Understanding what to watch for — and what's worth a call to your doctor — helps you stay safe while on testosterone replacement therapy.

Testim Boxed Warning: Secondary Testosterone Exposure

The FDA requires Testim to carry a boxed warning — the strongest warning the FDA issues — about the risk of secondary testosterone exposure to children and women. Cases have been reported where children and female partners who had skin contact with Testim application sites developed signs of virilization, including:

Enlarged genitals or clitoris in children

Premature development of pubic hair

Increased aggression or erections in children

Body hair changes or acne in female partners

To minimize this risk: wash your hands thoroughly after applying Testim, let the gel dry completely before getting dressed, cover the application site with clothing, and avoid direct skin contact with others until you've showered or washed the area.

Common Testim Side Effects (Reported in Clinical Trials)

The most common side effects seen in clinical trials of Testim (occurring in 2% or more of patients, more than placebo) were:

Application site reactions: Redness, itching, burning, or rash at the application site on the shoulders or upper arms

Increased hematocrit (polycythemia): Testosterone stimulates red blood cell production, which can thicken the blood. Your doctor will check hematocrit levels during treatment.

Other commonly reported side effects include:

Headache

Acne or oily skin

Mood changes (irritability, emotional shifts)

Gynecomastia (breast tissue enlargement in men)

Fluid retention / ankle swelling

Increased blood pressure

Serious Testim Side Effects to Know

The following serious side effects have been reported with Testim use. Seek immediate medical care if you experience any of these:

Venous thromboembolism (blood clots): DVT (leg pain, swelling, warmth, redness) or PE (chest pain, shortness of breath). The TRAVERSE study found a numerically higher rate of VTE with testosterone gel (1.7%) versus placebo (1.2%).

Cardiovascular events: Testim carries warnings about potential increased risk of heart attack and stroke, particularly in men with existing cardiovascular risk factors. The evidence is inconclusive — some studies show increased risk, others don't.

Sleep apnea: Testosterone may worsen sleep apnea, especially in obese patients or those with chronic lung disease. Report new or worsening snoring, gasping during sleep, or excessive daytime sleepiness.

Prostate issues: Testosterone may stimulate prostate growth. If you have an enlarged prostate (BPH), symptoms like urinary urgency, frequency, or weak stream may worsen. Prostate-specific antigen (PSA) should be monitored.

Fertility impairment: Testosterone suppresses natural sperm production (spermatogenesis). Men who wish to father children should discuss this risk with their doctor before starting TRT. Effects may be irreversible in some cases.

Polycythemia (excessive red blood cells): Can increase the risk of blood clots, stroke, and other cardiovascular complications. Requires regular monitoring of hematocrit.

When to Call Your Doctor Immediately

Chest pain, difficulty breathing, or sudden severe headache

Leg pain, swelling, or redness (possible DVT)

Prolonged or painful erections lasting more than 4 hours (priapism)

Signs of virilization in a child or female partner who has had skin contact

Significant ankle swelling or sudden weight gain (edema)

Mood changes including depression, anxiety, or aggressive behavior

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Monitoring Labs Your Doctor Should Order

While on Testim, expect your doctor to periodically check:

Serum testosterone level (to ensure you're in the normal range)

Hematocrit/CBC (polycythemia screening)

PSA (prostate-specific antigen)

Blood pressure and lipid panel

The Bottom Line

Most people tolerate Testim well, and common side effects like application site irritation are manageable. The bigger risks — blood clots, cardiovascular events, secondary exposure — require awareness and monitoring. Tell your doctor about any new or worsening symptoms while using Testim. For information on how Testim interacts with other medications, see our guide to Testim drug interactions. If you need help finding a pharmacy for your Testim prescription, visit medfinder.