What Side Effects Should You Expect on Testosterone?

Starting Testosterone replacement therapy (TRT) can be life-changing — more energy, better mood, improved libido. But like any medication, Testosterone comes with side effects. Most are mild and manageable. A few are serious enough to need medical attention.

This guide breaks down what to expect based on real clinical data, so you can feel confident about your treatment. If you're still learning about the medication, start with our overview: What Is Testosterone?

Common Side Effects

These are the side effects most men experience when starting TRT. They're usually mild and often improve after the first few weeks or months:

• Acne or oily skin — One of the most common effects, especially in the first few months. Keeping skin clean and using over-the-counter acne treatments can help.
• Injection site pain or irritation — If you're using Testosterone Cypionate or Enanthate injections, some soreness at the injection site is normal. Rotating injection sites helps.
• Fluid retention (edema) — Mild swelling in the ankles or feet. Usually resolves on its own but tell your doctor if it persists.
• Mood changes — Some men notice irritability or mood swings, especially early on. This often stabilizes as your body adjusts.
• Increased body hair — Testosterone can increase hair growth on the body while potentially accelerating hair loss on the scalp (male pattern baldness).
• Changes in libido — Most men see an increase, but some experience fluctuations as levels stabilize.
• Headache — Occasionally reported, usually mild.
• Application site reactions — If you use a gel (like AndroGel or Testim) or patch (Androderm), redness or itching at the application site is common.

Side Effects by Formulation

Different forms of Testosterone have slightly different side effect profiles. Here's a quick breakdown:

Injections (Testosterone Cypionate, Enanthate)

The most commonly prescribed form. Side effects include injection site pain, fluctuations in energy and mood between doses (peaks and troughs), and acne. Subcutaneous injections with Xyosted tend to cause less injection site pain than intramuscular injections.

Topical Gels (AndroGel, Testim, Fortesta, Vogelxo)

Common issues include skin irritation at the application site and the risk of transferring Testosterone to others through skin contact. This is especially dangerous for women and children. Always wash hands after applying and cover the area with clothing.

Patches (Androderm)

Skin reactions are the main concern — redness, itching, and blistering at the patch site are reported in up to 30% of users. Rotating the application site helps.

Oral Capsules (Jatenzo, Tlando, Kyzatrex)

These newer formulations can cause increased blood pressure, nausea, and headache. Jatenzo, Tlando, and Kyzatrex carry a boxed warning about the risk of elevated blood pressure and major cardiovascular events.

Nasal Gel (Natesto)

Nasal side effects like runny nose, nosebleeds, and nasal discomfort are common. Headache is also frequently reported.

Pellet Implants (Testopel)

Pellet extrusion (the pellet pushing back out through the skin) is the most unique risk. Infection at the implant site can also occur.

Serious Side Effects: When to Call Your Doctor

While most side effects are manageable, some require immediate medical attention. Contact your doctor right away if you experience:

Polycythemia (High Red Blood Cell Count)

This is the most common serious side effect of TRT. Testosterone stimulates red blood cell production, and if levels get too high, your blood becomes thicker — increasing the risk of blood clots, stroke, and heart attack. Your doctor should check your hematocrit (a measure of red blood cell concentration) regularly. If it goes above 54%, your doctor may reduce your dose or have you donate blood.

Cardiovascular Events

The FDA has issued warnings about potential increased risk of heart attack and stroke with Testosterone use. However, the large TRAVERSE trial found no significant increase in major cardiovascular events in men with hypogonadism taking Testosterone vs. placebo. Still, if you experience chest pain, sudden shortness of breath, or weakness on one side of your body, seek emergency care immediately.

Blood Clots (DVT and Pulmonary Embolism)

Symptoms include swelling, pain, or warmth in one leg (DVT) or sudden shortness of breath and chest pain (pulmonary embolism). Seek emergency care immediately.

Sleep Apnea

Testosterone can worsen or trigger obstructive sleep apnea. If your partner notices you've started snoring heavily or you wake up gasping for air, talk to your doctor.

Liver Problems

Primarily a concern with oral Testosterone formulations. Symptoms include yellowing of the skin or eyes, dark urine, and persistent nausea. This is less of a concern with injections and topical forms.

Allergic Reactions

Rare but possible, especially with Aveed (Testosterone Undecanoate injection), which carries a REMS requirement due to the risk of pulmonary oil microembolism (POME) and anaphylaxis. Aveed must be administered in a healthcare setting with observation afterward.

Long-Term Considerations

If you're on TRT for the long haul, there are a few things to keep in mind:

• Fertility: Exogenous Testosterone suppresses sperm production. If you're planning to have children, discuss this with your doctor before starting. Alternatives like Clomiphene or hCG may preserve fertility.
• PSA monitoring: Your doctor should check your PSA levels regularly to screen for prostate changes. Testosterone is contraindicated in men with known prostate cancer.
• Regular blood work: Expect to get blood drawn every 3–6 months initially, then at least annually. Key markers include total Testosterone, hematocrit, PSA, and lipid panel.
• Bone density benefits: Long-term TRT has been shown to improve bone density in men with hypogonadism, reducing fracture risk.

How to Manage Side Effects

Most Testosterone side effects can be managed with simple strategies:

• Acne: Use a gentle cleanser and benzoyl peroxide. If severe, ask your doctor about prescription treatments.
• Injection site pain: Rotate sites, use a smaller gauge needle, and warm the oil before injecting.
• Mood changes: Keep a mood journal. If irritability persists, your dose may need adjusting.
• Fluid retention: Reduce sodium intake and stay active.
• Hair loss: Talk to your doctor about finasteride or minoxidil if this is a concern.

If side effects are significantly impacting your quality of life, your doctor may adjust your dose, switch your formulation, or try a different treatment approach. Don't stop Testosterone abruptly without medical guidance — this can cause withdrawal symptoms and a crash in energy and mood.

The Bottom Line

Testosterone side effects are real, but for most men they're mild and manageable. The key is regular monitoring through blood work and open communication with your doctor. Know what's normal, know what's not, and don't hesitate to reach out if something feels off.

For more on how Testosterone works in your body, check out our guide on Testosterone's mechanism of action. And if you need to fill your prescription, check pharmacy availability with MedFinder.