Nebido (testosterone undecanoate)

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

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: Large peaks and troughs in T levels; more side effects due to this
• Availability: NHS or private prescription

If you’ve been reading about testosterone replacement therapy (TRT) online, you might have come across Nebido. It often appears in forums and on clinic websites as one of the long-acting injection options for men with confirmed low testosterone.

At Voy, we don’t prescribe Nebido. Our clinicians prefer other testosterone preparations that allow more flexible, steadier dosing. That said, many people still want to understand what Nebido is and how it fits into the wider picture of TRT.

Here's the lowdown on what it is, how it works, and how it compares with other TRT options.

What is Nebido?

Nebido is a brand name for testosterone undecanoate, a synthetic version of T, used to treat clinically low testosterone levels in men. Like other forms of TRT, it's prescribed to help with symptoms of low T such as low energy, reduced libido, poor mood, and decreased muscle strength.

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.

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)
• Hot flushes & possibly breast tissue growth (due to the large oestrogen peak effect)
• Acne (due to large T peak)
• Injection site reactions like bruising (due to large injection volume)

Did you know that Nebido can increase your oestrogen levels? Yep—as T goes up, some of it is converted into oestrogen. 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 oestrogen. Getting to a healthy weight can also lower your oestrogen 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 - you can't really personalise it to you.

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.

Nebido vs other testosterone options

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

Testosterone undecanoate vs cypionate

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

Nebido vs testosterone enanthate

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

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.

Why Voy doesn't offer Nebido

While the extended dosing interval might sound convenient, Nebido creates significant fluctuations in testosterone levels. More testosterone is released in the first few weeks after injection, causing unnaturally high levels initially, followed by a gradual decline as you approach your next injection. These peaks and troughs can lead to inconsistent symptom relief and side effects.

At Voy, we prefer TRT formulations with medium-length esters (like testosterone cypionate) that can be given in smaller, more frequent doses. This approach maintains steadier testosterone levels, resulting in more consistent symptom improvement and better overall outcomes.

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.