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

Like all medications, Jatenzo (testosterone undecanoate) can cause side effects. Some are mild and manageable; others are serious and require prompt medical attention. Understanding what to expect — and knowing which symptoms warrant a call to your doctor — is an essential part of safe testosterone replacement therapy.

This guide covers the most important Jatenzo side effects based on clinical trial data and the FDA-approved prescribing information, along with practical guidance on monitoring and when to seek care.

Most Common Side Effects of Jatenzo

In the pivotal 4-month clinical trial with 166 patients, the following side effects occurred in 2% or more of patients:

Headache — Occurred in 4.8% of patients. Most cases were mild; a few required treatment with pain relievers, and 2 patients stopped Jatenzo because of headaches.

Increased hematocrit (red blood cell count) — Occurred in 4.8% of patients. Elevated hematocrit increases the risk of blood clots, stroke, and heart attack. Your doctor will monitor this every 3 months.

Decreased HDL ("good") cholesterol — Testosterone can lower HDL levels, which may affect cardiovascular risk over time. Lipid monitoring is part of ongoing care.

High blood pressure (hypertension) — Jatenzo increased average systolic blood pressure by 4.9 mm Hg in clinical trials. 7% of patients needed to start or intensify blood pressure medication during the trial. Monitor BP approximately 3 weeks after starting or changing your dose.

Nausea — Usually mild; taking Jatenzo consistently with food (not on an empty stomach) helps minimize GI upset.

Serious Side Effects That Require Immediate Medical Attention

Call 911 or go to the emergency room immediately if you experience any of the following:

Signs of heart attack or stroke: Chest pain, sudden severe headache, numbness or weakness on one side of the body, difficulty speaking or understanding speech, sudden vision changes

Signs of blood clot (DVT or pulmonary embolism): Pain, swelling, redness, or warmth in a leg; sudden shortness of breath, chest pain, or coughing up blood

Side Effects to Report to Your Doctor (Non-Emergency)

Contact your prescriber at your next scheduled appointment or sooner if you notice:

Swelling of feet, ankles, or legs (edema) — Testosterone can cause sodium and water retention, which can worsen heart failure or kidney disease

Enlarged or painful breasts (gynecomastia) — Can develop during treatment; your doctor may adjust your dose

Changes in urination — Frequent nighttime urination, weak stream, urgency — may indicate enlarged prostate (BPH) or, rarely, prostate cancer

Sleep disturbances or worsened snoring — Jatenzo may potentiate sleep apnea, especially in patients who are overweight or have other risk factors

Mood changes, depression, or thoughts of self-harm — Depression and suicidal ideation have occurred during Jatenzo clinical trials; report any significant mood changes

Prolonged or frequent erections — May be a sign of supraphysiologic testosterone levels; contact your doctor for a dose check

Signs of liver problems — Jaundice (yellow skin or eyes), dark urine, upper-right abdominal pain, fatigue. Note: Jatenzo is not known to cause liver problems directly (unlike old oral testosterone products), but any signs of hepatic dysfunction should be reported

Blood Pressure: The Key Safety Consideration

Blood pressure elevation is one of the most clinically important safety concerns with Jatenzo. While the FDA removed the blood pressure boxed warning from Jatenzo's label in July 2025, BP monitoring is still required. Here's what you should do:

Check your blood pressure at home approximately 3 weeks after starting Jatenzo or after any dose change

Report any readings consistently above 130/80 mmHg to your doctor

Avoid over-the-counter decongestants (pseudoephedrine, phenylephrine) while on Jatenzo — they can raise BP further

Effects on Fertility

Large doses of androgens can suppress sperm production (spermatogenesis), potentially reducing fertility. If you plan to have children in the future, discuss this with your doctor before starting Jatenzo. In some cases, alternative treatments that preserve fertility (like clomiphene citrate) may be more appropriate.

The Bottom Line on Jatenzo Side Effects

Most Jatenzo patients tolerate the medication well when their dose is properly titrated and monitoring is maintained. The most important things you can do: keep your follow-up lab appointments, monitor your blood pressure, and report any unusual symptoms promptly. For more on what drugs to avoid while taking Jatenzo, see our guide on Jatenzo drug interactions.