Subcutaneous testosterone has been used for years in countries such as the United States, the United Kingdom and Canada, but in Spain it remains uncommon: the product information of the marketed preparations does not include that route of administration. A team from the Gender Identity Reference Unit at Hospital Universitario Doctor Peset (Valencia) has now published in Endocrinología, Diabetes y Nutrición its experience with 28 trans men treated with subcutaneous testosterone cypionate given once a week.
What was measured, and how
The work is an observational, retrospective, longitudinal study of patients seen between January 2024 and September 2025 at that reference unit. Twenty-eight trans men took part, including people starting treatment for the first time and others who had been on other testosterone formulations and switched route. The starting schedule was 50 milligrams of cypionate per week, injected under the skin. Follow-up looked at serum total testosterone and estradiol levels, liver function tests, lipid profile, haematocrit, the disappearance of menstruation, the appearance of acne and tolerance of the injections.
The results
- Stable levels within the male range. At two months, mean total testosterone was 6.2 nanograms per millilitre (standard deviation 2.9) and, at six months, 5.1 (1.5), always inside the physiological reference interval for men.
- Dose adjustments in a quarter of cases. Seven of the 28 participants (25%) needed some change in the schedule to stay within target.
- Amenorrhoea in 92.9%. Stopping menstruation, one of the most expected clinical goals and one with the greatest impact on the distress linked to gender incongruence, was achieved in almost all participants.
- No metabolic red flags. No clinically significant changes were seen in liver enzymes or in the lipid profile, and the incidence of polycythaemia — the excessive rise in red blood cells, one of the classic adverse effects of testosterone — was low.
- Good tolerance and acceptance. No local reactions at the injection site were recorded, and every participant reported satisfaction with this route.
Why the subcutaneous route matters
Hormone is released more gradually when injected under the skin than into muscle, which tends to give steadier concentrations and fewer peaks and troughs between doses. In practice, the subcutaneous route allows shorter, thinner needles, can be self-administered at home and reduces visits to have the injection given, which weighs on adherence to a treatment intended to last a lifetime. For many trans people it also means more control over their own hormone therapy, without depending on a clinic for every shot.
What this work cannot show
- It is a small study (28 people), retrospective, single-centre and without a comparison group: it can describe a clinical experience, not establish that this route is better than the others.
- Follow-up is six months. It offers no data on long-term effects on bone, cardiovascular risk, fertility or muscle mass.
- Satisfaction was recorded as acceptance of the route of administration, with the usual limits of a survey taken in clinic.
- The formulation is not indicated for subcutaneous use in its Spanish product information, so using it requires explicit information and consent from the patient.
For the non-specialist reader, the message is narrow but useful: a simpler route of administration can deliver adequate hormone levels with good acceptance in trans men, according to the experience of a single service. Turning that impression into a general recommendation would require larger studies with longer follow-up, something the team itself flags as the next step.
Source: Experience with subcutaneous testosterone for gender-affirming hormone therapy in transgender men at a tertiary care center. Tadeo Morant E, Rubio Puchol O, García Torres S, Cuñat Navarro E, García Malpartida K, Fernández Collazo P, de Miguel LF, Sanz Arilla G, Morillas Ariño C. Endocrinología, Diabetes y Nutrición 2026; art. 501799. DOI: 10.1016/j.endien.2026.501799.
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