Testosterone undecanoate is the long-acting injection most men have never heard of. While the typical guy on testosterone replacement therapy (TRT) sticks himself once or twice a week, men on undecanoate get a shot once every 10 to 14 weeks. That's four to five injections a year instead of fifty or more. The brand names are Aveed in the United States and Nebido across the UK, Europe, Australia, and much of the world.
It sounds like a dream: set it and forget it. But the long half-life is a double-edged sword. This guide breaks down exactly how undecanoate works, the loading schedule that gets you to steady levels, the real safety catch the FDA worries about, and the honest tradeoffs against a standard weekly ester like cypionate or enanthate.
Quick Answer
- What it is: Testosterone undecanoate is a very long-acting injectable testosterone in castor or tea-seed oil, sold as Aveed (US, 750 mg) and Nebido (Europe/UK, 1,000 mg). One injection lasts roughly 10 to 14 weeks.
- The loading schedule: Aveed is dosed at 750 mg on day 1, again at 4 weeks, then every 10 weeks. Nebido is 1,000 mg on day 1, again at 6 weeks, then every 10 to 12 weeks. Steady levels arrive by about the third injection.
- The big tradeoff: Far fewer injections and steadier levels than weekly esters — but you cannot quickly stop it if a side effect like high hematocrit shows up, and in the US it carries a boxed warning for pulmonary oil microembolism (POME), so each shot is given in a clinic with a 30-minute wait.
- Who it suits: Men with confirmed low testosterone who hate frequent needles and want convenience — and who don't mind that dose changes take months to take effect.
Medical disclaimer: This article is for education only and is not medical advice. Testosterone is a controlled substance and a prescription drug. Aveed is available in the US only through a restricted REMS program and must be injected by a trained healthcare provider. Do not start, stop, or change any testosterone protocol without a licensed physician who monitors your blood work. Statements here have not been evaluated as treatment for your specific situation.
What is testosterone undecanoate?
Testosterone undecanoate is testosterone with a long fatty-acid chain (undecanoic acid) attached. That chemical tail is the whole trick. The longer and fatter the ester chain, the slower your body releases active testosterone from the oily depot left in the muscle after injection.
Compare the esters by chain length and you can almost predict the dosing schedule:
| Ester | Common brand | Half-life (approx.) | Typical injection frequency |
|---|---|---|---|
| Propionate | Testoviron | ~2-3 days | Every 1-2 days |
| Enanthate | Delatestryl | ~4.5 days | Every 3.5-7 days |
| Cypionate | Depo-Testosterone | ~8 days | Every 3.5-7 days |
| Undecanoate (IM) | Aveed / Nebido | ~21-34 days (oil depot) | Every 10-14 weeks |
Undecanoate is in a class of its own. The injectable version sits in the muscle as an oil depot and releases for weeks. (There is also an oral testosterone undecanoate, sold as Jatenzo, Tlando, and Kyzatrex, but that's a twice-daily capsule with completely different pharmacology — this guide is about the injectable depot, not the pills.)
Want a refresher on how the standard esters stack up against each other before going long-acting? Our deep dive on testosterone cypionate vs enanthate vs propionate covers the short and medium esters in detail.
Aveed vs Nebido: same drug, different doses
Aveed and Nebido are the same molecule, but they are not interchangeable products. The US and rest-of-world versions were developed and approved separately, so the dose, oil carrier, and schedule differ.
| Feature | Aveed (US) | Nebido (Europe/UK/Australia) |
|---|---|---|
| Active drug | Testosterone undecanoate | Testosterone undecanoate |
| Dose per injection | 750 mg (3 mL) | 1,000 mg (4 mL) |
| Oil carrier | Castor oil + benzyl benzoate | Castor oil + benzyl benzoate |
| First gap (loading) | Second shot at 4 weeks | Second shot at 6 weeks |
| Maintenance interval | Every 10 weeks | Every 10-14 weeks |
| Restricted program | Yes — Aveed REMS | No formal REMS (still clinic-administered) |
| Approved | FDA, 2014 | EU, 2003-2004 |
Sources: FDA Aveed prescribing information and the Nebido Summary of Product Characteristics.
The practical upshot: a man in Manchester on Nebido and a man in Miami on Aveed are on the same drug, but the British patient gets a slightly larger dose at a slightly different schedule.
How does the long-acting injection actually work?
After the shot goes deep into the gluteal muscle, the oil forms a depot. Enzymes slowly cleave the undecanoate ester, freeing testosterone into the bloodstream a little at a time over weeks. There's no sharp spike-and-crash like you get with the short esters.
Here's what the pharmacokinetics look like for each product, straight from the labels:
| Metric | Aveed (750 mg) | Nebido (1,000 mg) |
|---|---|---|
| Time to peak after a dose | Median 7 days (range 4-42) | About 7 days |
| When steady state is reached | By the 3rd injection (~14-24 weeks) | Between the 3rd and 5th injection |
| Steady-state peak testosterone | Within normal range | ~42 nmol/L (~1,210 ng/dL) |
| Steady-state trough testosterone | Within normal range | ~17 nmol/L (~490 ng/dL) |
Sources: FDA Aveed label; Nebido SmPC.
A 2008 study in Clinical Endocrinology followed hypogonadal men on 1,000 mg Nebido and confirmed the steady-state pattern, while also noting that bigger and older men tended to run lower levels — a reminder that one dose does not fit all bodies (Moisey et al., 2008, PMID 18394021).
Why steadier levels matter
The classic complaint with weekly esters is the roller coaster. Testosterone spikes high a day or two after the shot, then slides toward the floor before the next one. Some men feel great early in the week and flat by the end.
A head-to-head pharmacokinetic study published in the European Journal of Endocrinology in 1995 compared injectable undecanoate against enanthate. Undecanoate produced "more favourable" pharmacokinetics — fewer supraphysiologic peaks and a much longer stretch in the normal range — while enanthate spiked to highly supraphysiological levels in the first five days and fell to the bottom of normal within about a month (Partsch et al., 1995, PMID 7711892).
That smoother curve is the selling point: fewer peaks, fewer troughs, fewer mood and libido swings tied to where you are in the injection cycle. If you want to understand how to read these levels on your own labs, see our guide on free vs total testosterone and SHBG.
What is the loading schedule?
The loading schedule is the front-loaded set of early doses that gets you to a useful blood level fast, before settling into the long maintenance rhythm. Because the drug is so slow, a single first shot isn't enough — you'd be waiting months to feel anything. So both products use a shorter first interval.
Aveed (US) schedule:
| Injection | Timing | Dose |
|---|---|---|
| 1st (initiation) | Day 1 | 750 mg |
| 2nd (loading) | Week 4 | 750 mg |
| 3rd onward (maintenance) | Every 10 weeks | 750 mg |
Nebido (Europe/UK) schedule:
| Injection | Timing | Dose |
|---|---|---|
| 1st (initiation) | Day 1 | 1,000 mg |
| 2nd (loading) | Week 6 | 1,000 mg |
| 3rd onward (maintenance) | Every 10-14 weeks | 1,000 mg |
With Nebido, the maintenance interval isn't fixed — your doctor adjusts it (anywhere from 10 to 14 weeks) based on your trough testosterone, measured just before the next injection is due. If your trough is too low, the interval shortens. If you're running high, it stretches. The 2018 Endocrine Society Clinical Practice Guideline endorses this trough-targeted approach for long-acting undecanoate (Bhasin et al., 2018, PMID 29562364).
Once you're at steady state, your provider will check labs roughly at the end of an interval to confirm you're holding in range. Curious what else gets tested? Our TRT blood work and monitoring schedule lays out the full panel.
What are the side effects and risks?
Undecanoate shares all the standard TRT side effects — acne, possible hematocrit rise, testicular shrinkage, fertility suppression, fluid retention — plus a couple that are specific to the long-acting oil depot.
The headline risk: POME and anaphylaxis
The FDA gives Aveed a boxed warning (the strongest type) for two injection-related events:
- Pulmonary oil microembolism (POME): tiny droplets of the injected oil reach the lungs. Symptoms include an urge to cough, shortness of breath, throat tightening, chest pain, dizziness, and fainting — usually during or right after the shot.
- Anaphylaxis: a severe, sometimes life-threatening allergic reaction.
These can happen after any injection, even after years of uneventful shots, not just the first one. A postmarketing safety analysis published in Sexual Medicine in 2020 reviewed real-world reports and found POME events were rare; most lasted only a few minutes and resolved with supportive care, though a minority needed emergency treatment (Pastuszak et al., 2020, PMID 32184081).
Because of this, Aveed is sold in the US only through the AVEED REMS Program, a restricted safety system. Practically, that means:
- You can't pick it up at a pharmacy and self-inject.
- A certified healthcare provider gives every shot.
- You stay in the clinic for 30 minutes of observation after each injection.
That 30-minute wait, ten or so times a year, is the convenience tax on this drug. Nebido in Europe doesn't carry a formal REMS, but it's still administered by a clinician with similar caution.
Side effects at a glance
| Side effect | Why it happens | What to do |
|---|---|---|
| POME / cough on injection | Oil droplets reach lungs | Clinic gives shot slowly, deep IM; 30-min observation |
| High hematocrit (thick blood) | Testosterone boosts red blood cells | Routine CBC; donate blood or adjust dose |
| Injection-site pain | Large oil volume (3-4 mL) | Warm the vial, slow injection |
| Mood swings | Hormonal shifts | Monitor; a leading reason men discontinue |
| Acne / oily skin | Androgen effect on skin | Topicals, dose review |
| Testicular shrinkage, low fertility | Shuts down natural production | HCG or enclomiphene if fertility matters |
| Estrogen-related (water, gyno) | Testosterone aromatizes to estradiol | Monitor estradiol; treat only if symptomatic |
Hematocrit deserves special attention with undecanoate. Long-acting injectables are linked to a higher rate of erythrocytosis (hematocrit climbing past ~52%) than gels. And here's the catch unique to this drug: if your blood gets too thick, you can't just skip a shot and clear it fast — the testosterone keeps releasing for weeks. Our guide on high hematocrit on TRT and how to lower it explains phlebotomy and dose-spacing strategies. For the broader picture, see TRT side effects and safety.
How does undecanoate compare to weekly esters?
This is the real decision most men face: the long-acting depot versus a standard weekly injection of cypionate or enanthate. Each wins on different fronts.
| Factor | Testosterone undecanoate (Aveed/Nebido) | Weekly ester (cypionate/enanthate) |
|---|---|---|
| Injections per year | 4-5 | 52-104 |
| Who injects | Clinic / provider (US) | Usually self-injected at home |
| Level stability | Very stable, few peaks/troughs | More peak-and-trough; depends on frequency |
| Dose flexibility | Poor — locked in for ~3 months | Excellent — tweak any week |
| Stop quickly if needed | No — washes out over months | Yes — clears in days to weeks |
| Cost per dose | High (often $1,000+ per vial in US) | Low ($20-100/month typical) |
| Self-administration | No (US, REMS) | Yes |
| Boxed warning (POME) | Yes (Aveed) | No |
The honest summary: undecanoate trades flexibility for convenience. If you value not thinking about needles and want smooth levels, it's appealing. If you want to fine-tune your dose, manage a rising hematocrit fast, or keep costs down, a weekly self-injected ester is usually the better fit.
Many men split the difference by self-injecting cypionate twice a week, which smooths the curve without the long-acting lock-in. If you're weighing how and where to inject, our guide on subcutaneous vs intramuscular testosterone injections is a good next read, along with the broader TRT delivery methods comparison covering gels, pellets, and nasal options. You can also model the numbers side by side with our TRT cost calculator.
The flexibility problem, spelled out
Say you start undecanoate and your hematocrit jumps to 55% two months in. With a weekly ester, you'd drop your dose immediately and watch the number fall over the next few weeks. With undecanoate, you're stuck — the depot keeps feeding testosterone regardless. Research in people who discontinued long-acting undecanoate for erythrocytosis found that hematocrit improved but testosterone stayed elevated for months afterward, because the drug simply hadn't cleared yet. That slow washout is the core downside of going long-acting.
This is why most providers want to confirm you tolerate testosterone — often with a short-ester trial first — before committing you to a drug you can't take back for a quarter of a year.
How much does it cost?
Cost is where undecanoate often loses. In the US, Aveed is an expensive branded drug with no generic. List prices commonly run over $1,000 per vial, and some sources quote closer to $2,000 per injection before insurance or assistance, per GoodRx and Drugs.com. Add the clinic administration fee and 30-minute observation each visit.
| Cost element | Aveed (US) | Weekly cypionate (US, cash) |
|---|---|---|
| Drug per dose | $1,000-2,000 per vial | $20-100 per month of vials |
| Doses per year | 4-5 | 12 months of supply |
| Administration | Clinic fee each visit | Self-injected (free) |
| Insurance | Sometimes covered with prior auth | Often covered; cheap cash too |
The manufacturer runs a copay assistance program that can cut out-of-pocket costs for commercially insured patients to as little as $0, covering up to $300 per injection (call the program to confirm eligibility). Nebido in countries with national health systems is far cheaper than the US Aveed price.
Bottom line: even at four shots a year, branded undecanoate is usually pricier than self-injected generic cypionate. For a full breakdown across delivery methods and clinic types, see how much does TRT cost and run your own numbers in the cost calculator.
Who is a good candidate?
Undecanoate isn't first-line for everyone, but it fits certain men well.
Good fit if you:
- Have confirmed low testosterone on two morning blood tests, with symptoms (the diagnosis standard in the 2018 Endocrine Society guideline).
- Hate frequent needles or can't reliably self-inject.
- Want the steadiest possible levels.
- Have stable hematocrit and no history of erythrocytosis.
- Can get to a clinic for administration and the 30-minute wait.
Probably not the best fit if you:
- Want to fine-tune your dose often.
- Run high hematocrit and need to react fast.
- Are trying to preserve fertility right now (talk about HCG or enclomiphene first).
- Are cost-sensitive or uninsured.
- Are still figuring out whether testosterone agrees with you at all.
Not sure you even need treatment yet? Start with do I need TRT — low testosterone symptoms and how it's diagnosed before getting attached to any one formulation.
How do you start and monitor it safely?
Whatever ester you land on, the safety scaffolding is the same: confirm the diagnosis, screen for risks, treat, then monitor on a schedule.
A reasonable roadmap looks like this:
- Confirm low T. Two separate morning total-testosterone tests below the lab's reference range, plus symptoms. Don't diagnose off one number or an afternoon draw.
- Baseline screening. Hematocrit, PSA (if age-appropriate), estradiol, and a fertility conversation up front.
- Pick the formulation with your provider based on lifestyle, fertility goals, cost, and how fast you may need to adjust.
- Load, then maintain. Follow the loading schedule above; settle into the 10-14 week rhythm guided by trough labs.
- Monitor. Recheck testosterone, hematocrit, and PSA at intervals your provider sets — typically at 3-6 months, then yearly once stable.
The Endocrine Society recommends measuring testosterone with long-acting undecanoate just before the next injection (the trough) and aiming to keep that trough in the mid-normal range. For prostate safety context, see TRT and your prostate — PSA, cancer risk, and BPH, and for the cardiovascular picture, the TRAVERSE trial breakdown.
Choosing where to get treated matters as much as the drug. A legit clinic monitors your labs, adjusts properly, and won't hand a long-acting injection to someone who hasn't been worked up. Compare your options with how to choose a TRT provider and our directory of vetted TRT providers. You can also compare clinics and protocols side by side.
Frequently asked questions
How long does one testosterone undecanoate injection last?
A single maintenance dose lasts about 10 to 14 weeks. Aveed (750 mg) is given every 10 weeks at steady state, and Nebido (1,000 mg) every 10 to 14 weeks depending on your trough testosterone level. That works out to roughly four to five injections a year. During loading, the second dose comes sooner — at 4 weeks for Aveed and 6 weeks for Nebido.
Can I inject testosterone undecanoate at home?
In the United States, no. Aveed is restricted under the AVEED REMS Program because of the risk of pulmonary oil microembolism and anaphylaxis. A certified healthcare provider must give every injection, and you wait 30 minutes afterward in the clinic. In some other countries, Nebido may be administered in a clinic setting too, though rules vary — ask your prescriber.
What's the difference between Aveed and Nebido?
They're the same drug — testosterone undecanoate — packaged differently. Aveed (US) is 750 mg per injection on a day 1, week 4, then every-10-week schedule. Nebido (Europe, UK, Australia) is 1,000 mg on a day 1, week 6, then every-10-to-14-week schedule. Aveed carries a US REMS restriction; Nebido does not, but both are clinician-administered.
Why would someone choose undecanoate over weekly testosterone?
The main reasons are convenience and steady levels. Four to five clinic visits a year beats 50-plus self-injections, and the long depot avoids the weekly peak-and-trough swings some men dislike. The tradeoffs are higher cost, no quick way to stop or lower the dose, and the POME warning. Many men who want flexibility stick with self-injected cypionate or enanthate instead.
Does undecanoate cause less estrogen or hematocrit trouble?
Not really. Because it's still testosterone, it aromatizes to estradiol and raises red blood cells like any other form. In fact, long-acting injectables are associated with a higher rate of erythrocytosis than gels, and the slow washout makes a high hematocrit harder to fix quickly. Routine blood work and, if needed, estrogen management still apply.
Related guides
- Testosterone Cypionate vs Enanthate vs Propionate: Which Ester Is Best?
- TRT Delivery Methods: Injections vs Cream vs Pellets vs Nasal
- Subcutaneous vs Intramuscular Testosterone Injections: Which Is Better?
- High Hematocrit on TRT: Why It Happens and How to Lower It
- TRT Dosage Guide: How Much Testosterone Should You Take Per Week?
- How Much Does TRT Cost? Telehealth vs Clinic vs Insurance
Sources
- FDA. Aveed (testosterone undecanoate) Prescribing Information, 2021. https://www.accessdata.fda.gov/drugsatfda_docs/label/2021/022219s015lbl.pdf
- Bayer / emc. Nebido 1,000 mg/4 mL Summary of Product Characteristics. https://www.medicines.org.uk/emc/product/14631/smpc
- Bhasin S, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2018. PMID 29562364. https://academic.oup.com/jcem/article/103/5/1715/4939465
- Partsch CJ, et al. Injectable testosterone undecanoate has more favourable pharmacokinetics and pharmacodynamics than testosterone enanthate. Eur J Endocrinol. 1995. PMID 7711892. https://pubmed.ncbi.nlm.nih.gov/7711892/
- Moisey R, et al. Serum testosterone and bioavailable testosterone correlate with age and body size in hypogonadal men treated with testosterone undecanoate (1,000 mg IM — Nebido). Clin Endocrinol. 2008. PMID 18394021. https://pubmed.ncbi.nlm.nih.gov/18394021/
- Pastuszak AW, et al. Occurrence of Pulmonary Oil Microembolism After Testosterone Undecanoate Injection: A Postmarketing Safety Analysis. Sex Med. 2020. PMID 32184081. https://pubmed.ncbi.nlm.nih.gov/32184081/
- Endocrine Society. Testosterone Therapy for Hypogonadism Guideline Resources. https://www.endocrine.org/clinical-practice-guidelines/testosterone-therapy
- GoodRx. Aveed Prices, Coupons & Savings Tips, 2026. https://www.goodrx.com/aveed
- Drugs.com. Aveed Prices, Coupons, Copay Cards & Patient Assistance. https://www.drugs.com/price-guide/aveed
Last reviewed: June 2026. This guide is educational and not a substitute for personalized medical advice.