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Last updated: Mar 03, 2021
5 min read

Testosterone undecanoate: uses and side effects

steve silvestro

Medically Reviewed by Steve Silvestro, MD

Written by Amro Alhelawe, PharmD


If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

Testosterone (T) therapy comes in many different forms nowadays. From a gel that you apply to your skin to a recently approved oral version of T, long gone are the days when T therapy always has to involve injecting yourself. 

In this article, we’ll explore one type of testosterone that’s available as an oral medication (as well as the standard needle-in-the-muscle variety). 

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What is testosterone undecanoate?

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 after the first two doses (Corona, 2014). You’d still 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 is a recently approved form of testosterone undecanoate that comes in a capsule taken twice a day. It’s the only oral version of testosterone available in the U.S. (Swerdloff, 2020). 

People who start testosterone therapy can generally see results from it within the first 1–2 months. It takes about six months to see improvements in bone strength and mineral density (Saad, 2011). 

What’s the difference between testosterone undecanoate and other forms of T?

There are a few different versions of T available by prescription (Petering, 2017):

The advantages 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, of course, since this is the only form of testosterone also available in oral form, your healthcare provider may prescribe testosterone undecanoate to you 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 when indicated (Petering, 2017). Be sure to take the dose prescribed by a healthcare professional.

What is testosterone undecanoate useful in treating?

Testosterone is known as an androgen or male sex hormone. But it actually has involvement in many bodily functions in both men and women. 

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, the most common of which is age. Other causes of low testosterone (called hypogonadism) include (Minnemann, 2008):

  • 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
  • Chemotherapy or damage from alcohol or heavy metals

Having 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 (Mulhall, 2018). 

T has also shown significant benefits when prescribed to transgender men suffering from gender dysphoria. It has been demonstrated in studies that taking T can (Irwig, 2017): 

  • 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 study demonstrated that testosterone undecanoate is safe and effective over five years of follow-up. Although the trial only had 50 participants, symptoms of gender dysphoria diminished, and satisfaction was achieved (Gava, 2018). Patients in another clinical study reported improved muscle strength and body composition (Gava, 2021).

Who should avoid taking T?

Older patients suffering from medical conditions like heart failure or uncontrolled hypertension have a greater risk of side effects. Although younger patients experience benefits from taking testosterone therapy, older patients may have a higher risk of heart problems (Elagizi, 2018).

T should never be given to patients with breast cancer, prostate cancer, and specific blood conditions.

What are the possible side effects of taking testosterone?

Testosterone replacement therapy offers remarkable benefits for those that need it. But it does come with some risks, and those risks are more significant in older people and in those with heart conditions.

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 (though mostly rare) of adverse events, including (Basaria, 2010):

People taking any form of testosterone can experience an allergic reaction, although it is pretty rare. 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.

It is also possible that T can interact with other medications that you take. For example, taking warfarin or other blood thinners while taking T can increase bleeding risk and should be avoided. Talk to your healthcare provider about the medications you take before starting any form of testosterone therapy.


  1. Basaria, S., Coviello, A. D., Travison, T. G., Storer, T. W., Farwell, W. R., Jette, A. M., et al. (2010). Adverse events associated with testosterone administration. The New England Journal of Medicine, 363(2), 109–122. doi: 10.1056/NEJMoa1000485. Retrieved from 
  2. Corona, G., Maseroli, E., & Maggi, M. (2014). Injectable testosterone undecanoate for the treatment of hypogonadism. Expert Opinion on Pharmacotherapy, 15(13), 1903–1926. doi: 10.1517/14656566.2014.944896. Retrieved from
  3. Elagizi, A., Köhler, T. S., & Lavie, C. J. (2018). Testosterone and Cardiovascular Health. Mayo Clinic Proceedings, 93(1): 83–100. doi: 10.1016/j.mayocp.2017.11.006. Retrieved from
  4. Gava, G., Mancini, I., Cerpolini, S., Baldassarre, M., Seracchioli, R., & Meriggiola, M. C. (2018). Testosterone undecanoate and testosterone enanthate injections are both effective and safe in transmen over 5 years of administration. Clinical Endocrinology, 89(6), 878–886. doi: 10.1111/cen.13821. Retrieved from
  5. Gava, G., Armillotta, F., Pillastrini, P., Giagio, S., Alvisi, S., Mancini, I., et al. (2021). A Randomized Double-Blind Placebo-Controlled Pilot Trial on the Effects of Testosterone Undecanoate Plus Dutasteride or Placebo on Muscle Strength, Body Composition, and Metabolic Profile in Transmen. The Journal of Sexual Medicine, 18(3): 646-655. Advance online publication. doi: 10.1016/j.jsxm.2020.12.015. Retrieved from
  6. Irwig, M. S. (2017). Testosterone therapy for transgender men. The Lancet. Diabetes & Endocrinology, 5(4), 301–311. doi: 10.1016/S2213-8587(16)00036-X. Retrieved from
  7. Minnemann, T., Schubert, M., Freude, S., Hübler, D., Gouni-Berthold, I., Schumann, C., et al. (2008). Comparison of a new long-acting testosterone undecanoate formulation vs. testosterone enanthate for intramuscular androgen therapy in male hypogonadism. Journal of Endocrinological Investigation, 31(8), 718–723. doi: 10.1007/BF03346421. Retrieved from
  8. Mulhall, J. P., Trost, L. W., Brannigan, R. E., Kurtz, E. G., Redmon, J. B., Chiles, K. A., et al. (2018). Evaluation and Management of Testosterone Deficiency: AUA Guideline. The Journal of Urology, 200(2), 423–432. doi: 10.1016/j.juro.2018.03.115. Retrieved from
  9. Petering, R. C. & Brooks, N. A. (2017). Testosterone Therapy: Review of Clinical Applications. American Family Physician, 96(7), 441–449. Retrieved from
  10. Saad, F., Aversa, A., Isidori, A. M., Zafalon, L., Zitzmann, M., & Gooren, L. (2011). Onset of effects of testosterone treatment and time span until maximum effects are achieved. European Journal of Endocrinology, 165(5), 675–685. doi: 10.1530/EJE-11-0221. Retrieved from
  11. Swerdloff, R. S., Wang, C., White, W. B., Kaminetsky, J., Gittelman, M. C., Longstreth, J. A., et al. (2020). A New Oral Testosterone Undecanoate Formulation Restores Testosterone to Normal Concentrations in Hypogonadal Men. The Journal of Clinical Endocrinology and Metabolism, 105(8), 2515–2531. doi: 10.1210/clinem/dgaa238. Retrieved from

Dr. Steve Silvestro is a board-certified pediatrician and Manager, Medical Content & Education at Ro.