What are these two injections?
The two most widely used intramuscular testosterone injections are testosterone enanthate and testosterone undecanoate. Both are testosterone attached to a different chemical group, called an ester, which controls how quickly the hormone is released from muscle into the blood.[1]
The main difference is therefore release duration and injection schedule, not strength, and doses of the two cannot be converted directly.[1]
Why the difference matters
Many users see hormone curves online and try to adjust their own injection timing or dose to feel better. This can push levels too high, thicken the blood or cause other side effects. Understanding how each product releases helps prevent inappropriate changes.[1]
Blood testing is the other reason. The right time to test differs between the two, and testing at the wrong time can lead to the wrong decision.
When injections are used
Injections are one option for men with confirmed deficiency and symptoms. The prevalence of low results is not the number of men who should receive testosterone.[1] Which products are available and commonly used also differs between countries.
Hormone levels after each injection
Testosterone enanthate is shorter-acting and is usually given every one to three weeks, as prescribed. Levels rise high in the first few days and then fall, becoming low before the next dose.[1],[2] Some men notice energy, mood or desire rising and falling with the cycle, and the peaks can raise haematocrit more readily.
Testosterone undecanoate is long-acting. After a first and second injection about six weeks apart, it is usually given roughly every 10–14 weeks. Levels are steadier, with smaller peaks and troughs.[1],[2]
Actual levels depend on the product, dose, body weight and individual response, so measured blood levels, not generic curves, guide treatment.[1]
How treatment is monitored
Monitoring combines symptoms, correctly timed blood tests, haematocrit and side effects, rather than a generic curve.[1],[2]
- For enanthate, the Endocrine Society recommends measuring testosterone midway between injections to reflect the average level.[2]
- For undecanoate, levels are usually checked at the end of the interval, just before the next injection, to make sure they are not too low.[2]
- For both, haematocrit and blood pressure are checked regularly, and the prostate is assessed according to age and risk.[1],[3]
Choosing between them
Several factors are weighed together: symptoms that fluctuate with the cycle, haematocrit, medical conditions, travel and cost.[1],[2] For example, men who notice marked mood swings across the cycle, or whose haematocrit rises easily, may benefit from a long-acting product, while those who need fine dose adjustment or are mindful of cost may choose the shorter-acting one.
Injections must be given by an appropriate provider, following each product's specific precautions. Undecanoate is a large oily injection that should be given slowly into the muscle, with observation afterwards as the product information requires, because rare episodes of temporary coughing or breathing difficulty from the oil have been reported.[1],[3]
How we care for you at Dr. Kris Clinic
We explain the differences between injections in plain language and choose together based on symptoms, blood results and lifestyle, in English or Thai. Injections are given in the clinic by health professionals, with blood tests timed to suit the product.
If you are already using injectable testosterone from elsewhere, we are happy to review your history and previous results without judgement and make your plan safer.
Frequently asked questions
Which one is better?
Neither is better for everyone. They differ in injection interval and how much levels rise and fall. Your doctor chooses based on symptoms, results and convenience.
My mood swings on enanthate. Is that normal?
It can happen because levels rise and fall with each cycle. Tell your doctor so the interval or product can be reviewed; do not adjust it yourself.
When should my blood be tested?
It depends on the product: usually midway between doses for enanthate, and just before the next dose for undecanoate.
Can I switch from one to the other?
Yes, under medical supervision, with a planned changeover and new monitoring, because doses do not convert directly.
Testosterone enanthate and undecanoate differ in release duration and injection interval. Base the schedule on the product and your measured response.[1] A generic curve can never replace blood tests of your own levels.
Talk to a doctor about this
Confidential care in Surat Thani, the mainland gateway to Koh Samui, Koh Phangan and Koh Tao. Tue–Fri 17:00–20:00 · Sat–Sun 10:00–15:00 (UTC+7)
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Dr. Krida Uakridathikarn (Dr. Kris)
Board-certified family physician with certificate training in clinical sexology and sexual medicine. He works at Suratthani Hospital and provides sexual health, hormone and LGBTQ+ inclusive care at Dr. Kris Clinic. Profile and CV
References
- EAU Guidelines 2026: Male Hypogonadism
- Endocrine Society: Testosterone Therapy for Hypogonadism (2018)
- FDA: Testosterone Information; June 2026 labelling update
Keep reading
Main guide: Men's sexual health
Low Testosterone: Symptoms and How It Is Properly Diagnosed
Tests Before Starting Testosterone Therapy (TRT)
Testosterone Injections or Gel: How They Differ and How to ChooseThis article is general education, not personal medical advice or a promise of results. Diagnosis and treatment require assessment by a doctor. Content reflects the cited sources as of the update date.