Head to head
Somatropin against Testosterone
The two hormones most often prescribed together in anti-ageing clinics, and the two with the most different evidence bases. Testosterone has a 5,246 man randomised cardiovascular safety trial behind it; growth hormone in healthy older adults has no equivalent, and is not approved for ageing.
Column A
SomatropinSomatropin (recombinant human growth hormone)
FDA-approved recombinant human growth hormone used for growth hormone deficiency and several other approved indications.
Column B
TestosteroneTestosterone, the principal androgen
The best-evidenced hormone on this site. A 5,246-man randomised trial settled the cardiovascular question, and 36 randomised trials in 8,480 women cover the half of the population nobody talks about.
Side by side, on the facts we can check
| Attribute | Somatropin | Testosterone |
|---|---|---|
| Category | Growth Hormone | Hormone |
| FDA status | FDA-approved for GH deficiency and other indications | FDA-approved for male hypogonadism in multiple formulations. Schedule III controlled substance in the United States. No testosterone product is approved for women in the United States, which is a documented gap rather than a judgement on the evidence. |
| Half-life | ~3-4 hours (subcutaneous) | Free testosterone itself clears in minutes to hours. What determines dosing is the ester: cypionate and enanthate run roughly eight days, propionate under a day, and undecanoate several weeks. The ester pages cover what that means in practice. |
| Molecular weight | 22,124 Da | 288.4 Da. A steroid, not a peptide. |
| Mechanism | Directly activates growth hormone receptors, raising IGF-1 and driving growth, protein synthesis, and metabolic effects. | A 19-carbon steroid synthesised from cholesterol, mainly in the Leydig cells of the testis under luteinising hormone control, and in smaller amounts by the ovary and adrenal in women. It acts directly on the androgen receptor, a nuclear receptor that binds DNA and alters transcription. Two conversions matter clinically: 5-alpha-reductase converts it to dihydrotestosterone, a more potent androgen responsible for much of the effect on scalp hair and prostate, and aromatase converts it to oestradiol, which is responsible for much of its effect on bone, mood and libido in men. Exogenous testosterone suppresses luteinising hormone and follicle-stimulating hormone through negative feedback, which is why it reduces sperm production and testicular size. |
| Human studies cited | 2 | 2 |
| Legal status, US | FDA-approved, prescription only | FDA-approved, prescription only |
Frequently asked questions
What is the difference between Somatropin and Testosterone?
Somatropin: FDA-approved recombinant human growth hormone used for growth hormone deficiency and several other approved indications. Testosterone: The best-evidenced hormone on this site. A 5,246-man randomised trial settled the cardiovascular question, and 36 randomised trials in 8,480 women cover the half of the population nobody talks about.
Which has stronger research evidence, Somatropin or Testosterone?
This database does not grade compounds. It counts what was run in people: 2 of the 3 studies cited on the Somatropin profile were human work, against 2 of 5 for Testosterone. Those counts are of our own citation lists and understate any larger literature, and neither is a recommendation.
Are Somatropin and Testosterone FDA-approved?
Somatropin: FDA-approved for GH deficiency and other indications. Testosterone: FDA-approved for male hypogonadism in multiple formulations. Schedule III controlled substance in the United States. No testosterone product is approved for women in the United States, which is a documented gap rather than a judgement on the evidence..
Reviewed Sep 2026. This page sets two published records side by side. It is educational, it is not medical advice, and it contains no dosing protocols or recommendations for personal use.