Testosterone undecanoate: uses and side effects

Testosterone (T) therapy comes in many different forms. From a gel that you apply to your skin to a recently approved oral medication, long gone are the days when T therapy had to mean injecting yourself with a needle. 

Testosterone undecanoate is one FDA-approved form of testosterone therapy that's available both as a long-acting injectable and as an oral medication. It can be beneficial for the treatment of hypogonadism and gender dysphoria. Continue reading to learn more about testosterone undecanoate. 

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Testosterone undecanoate comes in two forms—an injectable form and an oral form. 

The injectable form is most commonly prescribed under the brand name Aveed, which is a long-acting testosterone injection that only requires five injections per year. You’d need to give yourself an intramuscular injection, which can be uncomfortable, but this form of T has a long half-life. This means fewer injections each year than the other forms of testosterone available.

Jatenzo, Kyzatrex, and Tlando are all approved forms of testosterone undecanoate that come in capsules taken twice a day. 

People who start testosterone therapy can generally see masculinization results (body and facial hair growth, deepening of the voice, etc.) within the first 1–2 months, while bone and muscle changes can take 6–12 months. 

In addition to testosterone undecanoate, there are a other versions of T available by prescription:

• Testosterone cypionate, injectable (Depo-Testosterone)

• Testosterone enanthate, injectable (Delatestryl)

• Intranasal gel (Natesto)

• Topical gel (Androgel, Fortesta, Testim)

The main advantage of taking injectable testosterone undecanoate over the other forms of injectable testosterone is that it requires fewer injections per year. This can be beneficial if you have trouble giving yourself a weekly injection. And, since testosterone undecanoate is the only form of testosterone also available in oral form, your healthcare provider may prescribe testosterone undecanoate if you’re a good candidate for oral testosterone therapy. 

There are small differences in dosing and absorption between these different forms of testosterone. But, long story short, they’re all effective at raising your serum testosterone to “normal” levels. As with any medication, be sure to take the dose exactly as prescribed by a healthcare professional.

Testosterone is known as an androgen or “male” sex hormone. But it’s actually a critical component in many bodily functions for all people. 

T plays a role in the development of masculine features like body hair and lean muscle. It also plays a role in your bones’ strength and the way you process cholesterol. T levels can decrease for numerous reasons, and naturally decline with age. Other causes of low testosterone (or hypogonadism) include:

• Damage to the pituitary gland (a gland in the brain responsible for sending the signal to your testes to make testosterone)

• Deficiency of certain hormones

• Cancer treatments

• Obesity

Low testosterone can cause mood changes, bone mineral density loss, and sexual dysfunction. Clinical trials have demonstrated that T is safe and effective in treating hypogonadism symptoms in cisgender men. 

T has also shown significant benefits when prescribed to transgender men and nonbinary people who experience gender dysphoria. Studies show that T can achieve the following to treat gender dysphoria: 

• Increase facial and body hair

• Increase lean muscle mass and strength

• Decrease body fat

• Deepen the voice

• Increase sexual desire

• Stop menstruation 

• Reduce stress, anxiety, and depression in transgender men 

Another small study demonstrated that testosterone undecanoate is safe and effective over five years of follow-up. The symptoms of gender dysphoria diminished and satisfaction was achieved. Patients in another clinical study reported improved muscle strength and body composition.

Older patients suffering from medical conditions like uncontrolled hypertension have a greater risk of side effects and should use testosterone with caution.

T should not be given to patients with breast cancer, prostate cancer, and specific blood conditions.

Testosterone replacement therapy offers remarkable benefits for those that need it. But it does come with some risks.

Testosterone has the potential for abuse and should not be used in higher doses than prescribed. Taking T with anabolic steroids can cause life-threatening symptoms like a heart attack.

Whether you take injectable or oral T, there is some risk of side effects, including:

• Acne

• Alopecia (hair loss)

• Lower HDL cholesterol and increased triglycerides

• Hypertension (high blood pressure)

• Increased prostate-specific antigen (PSA) levels, which may be correlated with an increased risk of prostate cancer

• Increased breast cancer risk

Although rare, people taking any form of testosterone can experience an allergic reaction. If you experience side effects like hives, swelling, or difficulty breathing after your first dose, do not take your second dose and contact a healthcare provider.

If self-injections aren’t for you, oral testosterone undecanoate may be an option to treat low testosterone, gender dysphoria, and more. Whatever your concerns may be, make an appointment with your healthcare provider. They can help you develop a safe and effective treatment plan that meets your needs.

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Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

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Current version

February 17, 2023

Written by

Amro Alhelawe, PharmD

Fact checked by

Chimene Richa, MD

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About the medical reviewer

Chimene Richa, MD

Dr. Richa is a board-certified Ophthalmologist and medical writer for Ro.