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Home/Guides & Tips/Testosterone/

Nebido

TRT

Nebido (testosterone undecanoate)

Here’s the lowdown on Nebido, a type testosterone replacement therapy injection.

clinician image

Medically reviewed by Medical Director

Dr. Jeff Foster - Men’s Health & TRT Specialist

iconPublished 12th November 2025

Curious about trying testosterone replacement therapy (TRT)? It can help with symptoms of low T, like problems with libido and finding it hard to build muscle.

One option is Nebido injections. Read on to learn all about them.

Key insights

  • What is it: Testosterone injection
  • How it’s used: Given directly into muscle every 10-14 weeks
  • Who it’s for: Men with confirmed low testosterone
  • Pros: Less frequent injections than other types of TRT
  • Cons: Peaks and troughs in T levels; possible side effects
  • Availability: NHS or private prescription

What is Nebido?

Nebido is a treatment for men with clinically low testosterone. Nebido is a brand name for testosterone undecanoate, a synthetic version of T.

Compared to other TRT injections, Nebido takes much longer to be absorbed into your blood. That’s because the testosterone undecanoate molecule has a chain attached to it called an ester. This ester is very long—and the longer the ester, the more time it takes for the drug to be absorbed. So, you take Nebido every 10-14 weeks, rather than once or twice per week.

But in practice, more T is released over the first few weeks, leading to unnaturally high testosterone levels in the first two weeks after an injection and a dip in your levels as you near the time for your next injection. That’s why many clinics (including us) prefer preparations with medium-length esters: giving smaller, more frequent doses can help maintain steady levels.

How does Nebido work?

Nebido is injected directly into your muscle, where it collects (forming a “depot”). Testosterone is then released slowly into the blood.

Feeling drained and unfocused?
It might be low testosterone. Get answers fast with an at-home blood test.

Nebido side effects

Most people tolerate TRT well, but there’s a chance you’ll get side effects when taking Nebido. Symptoms include:

  • Abnormally high red blood cell count (this thickens your blood and can increase your blood pressure)
  • Acne
  • Hot flushes
  • Injection site reactions like bruising
  • Breast tissue growth

Did you know that Nebido can increase your estrogen levels? Yep—as T goes up, some of it is converted into estrogen. This explains side effects like breast tissue growth.

In up to 0.1% of people, the medicine (which contains oil) may reach the lungs. This might cause symptoms like coughing and shortness of breath, but these usually clear up within an hour.

And if you notice signs of an allergic reaction, like swelling of the face, lips or throat, call 999 or attend A&E as soon as you can.

How to deal with Nebido side effects

If Nebido isn’t agreeing with you, your provider might recommend swapping to another type of TRT, like testosterone enanthate or cypionate. Both are taken more frequently, meaning they could help keep your T levels steadier.

Or, they may suggest aromatase inhibitors, which prevent T from being converted into estrogen. Getting to a healthy weight can also lower your estrogen levels.

Who should avoid Nebido?

Steer clear of Nebido if:

  • You have, or have had liver cancer
  • You have a cancer that may grow if exposed to androgens, like prostate or breast cancer

And before starting Nebido, tell your doctor if you have or have ever had:

  • Epilepsy
  • Blood clotting problems
  • Heart, liver or kidney problems
  • Migraine
  • Sleep apnoea
  • Cancer
  • High blood pressure

They’ll consider this when deciding whether to prescribe it to you.

Nebido dosing schedule

There’s just the one set Nebido dose: 1000mg in a 4ml injection, that’s done every 10-14 weeks.

Where and how is Nebido injected?

Nebido testosterone injections are given directly into the muscle. The buttock is the preferred site because the muscle is big enough to handle the injection volume.

Note: This should be done by a qualified clinician. If you do it yourself, there’s a risk you’ll inject the oily liquid into a blood vessel.

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Nebido vs other testosterone options

But how do Nebido testosterone injections compare to other sorts of TRT?

Testosterone undecanoate vs enanthate

As a refresher: testosterone enanthate is an injection that’s taken more frequently (usually 1-2 x per week) than undecanoate. So, it may lead to steadier T levels.

Nebido vs testosterone cypionate

Cypionate is a medium ester that’s very similar to enanthate. Though it’s easier to inject—and therefore, may cause fewer injection site reactions—than enanthate because the formula is made with a different type of oil (olive vs sesame seed).

Nebido vs Sustanon

Sustanon is a blend of four esters that’s taken every 2-4 weeks. It contains peanut oil, so you shouldn’t take it if you’re allergic to peanuts or soya.

Nebido vs Testogel

And finally, we have Testogel, a gel that’s applied to the skin. It has low absorption of T and has been shown to be less effective than injectables.

Could low T be holding you back?

You don’t have to put up with low T symptoms. TRT can help bring your levels back into the normal range, boosting your strength, energy, libido, and more.

At Voy, we stock plenty of options that are more convenient and show better results than Nebido.

And you can start your journey right now. Take our quiz and order an at-home, testosterone blood test to see if TRT is right for you.

FAQ

FAQs about Nebido (testosterone undecanoate)

DisclaimerAt Voy, we ensure that everything you read in the Health Centre is medically reviewed and approved. However, the information provided is not meant to replace professional medical advice, diagnosis, or treatment. It should not be relied upon for specific medical advice.
References
icon¹

Adam, Jarren A., et al. “Occurrence of Pulmonary Oil Microembolism (POME) with Intramuscular Testosterone Undecanoate Injection: Literature Review,” International Journal of Impotence Researchscribble-underline, vol. 35, 2023:439-446. www.nature.com/articles/s41443-022-00585-1.

icon²

Cambell, Katherine, et al. “Safety Aspects and Rational Use of Testosterone Undecanoate in the Treatment of Testosterone Deficiency: Clinical Insights,” Drug, Healthcare and Patient Safety,scribble-underline vol. 15, 2023:73-84. https://pmc.ncbi.nlm.nih.gov/articles/PMC10072151/.

icon³

Figueiredo, Maria Gabriela, et al. “Testosterone Therapy with Subcutaneous Injections: A Safe, Practical, and Reasonable Option,” The Journal of Clinical Endocrinology and Metabolismscribble-underline, vol. 107, issue 3, 2021:614-626 https://pmc.ncbi.nlm.nih.gov/articles/PMC9006970/.

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“Nebido 1000mg/4ml solution for injection,” Electronic Medicines Compendium.scribble-underline www.medicines.org.uk/emc/product/14631/smpc#gref. Accessed 20 Oct. 2025.

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“Nebido 1000mg/4ml solution for injection - information for the user,” Electronic Medicines Compendiumscribble-underline, 2024. www.medicines.org.uk/emc/files/pil.14631.pdf. Accessed 20 Oct. 2025.

icon⁶

Osterberg, Charles E, et al. “Risks of Testosterone Replacement Therapy in Men,” Indian Journal of Urologyscribble-underline, vol. 30, issue 1, 2014:2-7 https://pmc.ncbi.nlm.nih.gov/articles/PMC3897047/.

icon⁷

Pastuszak, Alexander W., et al. “Comparison of the Effects of Testosterone Gels, Injections, and Pellets on Serum Hormones, Erythrocytosis, Lipids, and Prostate-specific antigen,” Sexual Medicinescribble-underline, vol. 3, issue 3, 2015:165-173 https://academic.oup.com/smoa/article/3/3/165/6956248.

icon⁸

Punjani, Nahid, et al. “The utilisation and impact of aromatase inhibitor therapy in men with elevated estradiol levels on testosterone therapy,” Sexual Medicinescribble-underline, vol. 9, issue 4, 2021:100378 https://pmc.ncbi.nlm.nih.gov/articles/PMC8360915/.

icon⁹

“Sustanon 250, 250mg/ml solution for injection,” Electronic Medicines Compendium,scribble-underline 2024. www.medicines.org.uk/emc/product/5373/smpc#gref/. Accessed 20 Oct. 2025.

icon¹⁰

Sizar, Omeed, et al. “Androgen Replacement,” in StatPearls, Treasure Island (FL): StatPearls Publishingscribble-underline 2023 https://www.ncbi.nlm.nih.gov/books/NBK534853/ Accessed 20 October 2025

icon¹¹

Stanik, S., et al. “The Effect of Weight Loss on Reproductive Hormones in Obese Men,” The Journal of Clinical Endocrinology and Metabolismscribble-underline, vol. 53, issue 4, 1981:828-832 https://academic.oup.com/jcem/article-abstract/53/4/828/2677805.

icon¹²

Turner, Leo, et al. “Pharmacokinetics and Acceptability of Subcutaneous Injection of Testosterone Undecanoate,” Journal of the Endocrine Society,scribble-underline vol. 3, issue 8, 2019:1531-1540 https://pmc.ncbi.nlm.nih.gov/articles/PMC6676071/.

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