Testosterone
Also known as: testosterone gel, testosterone injection, androgen, testosterone replacement therapy, TRT
The main androgen, given as a gel, patch, injection or implant to replace what the testes cannot make in confirmed hypogonadism and as the masculinising hormone in gender-affirming care for trans men and non-binary people. It is not a treatment for ageing or a way to build muscle, and its use needs regular blood monitoring.
- Generic name
- Testosterone
- Active ingredient
- Testosterone (variants: testosterone undecanoate, testosterone enantate, testosterone cipionate, testosterone propionate)
- Product type
- Small-molecule medicine
- Drug class
- Androgens
- Brand names
- UK Testogel, Tostran, Nebido, Sustanon · US AndroGel, Testim, Depo-Testosterone
- Routes
- Transdermal, Intramuscular, Topical, Implant
- Dosage forms
- Gel, Injection, Depot (long-acting) injection, Patch, Implant, Capsule
- Also known as
- testosterone gel, testosterone injection, androgen, testosterone replacement therapy, TRT
- Usual preparations
- Gel applied to the skin of the shoulders, upper arms or abdomen every day, and a transdermal patch; Intramuscular injections: shorter-acting esters given every few weeks and a long-acting undecanoate preparation given every few months; subcutaneous injection is used in some services; Subcutaneous implants (pellets) and oral capsules, which are used less often (summary of the cited reference, not a prescription)
- Onset and duration
- Energy, mood and libido may change within a few weeks. In masculinising therapy periods usually stop within two to six months, the clitoris enlarges and the voice deepens over the first year, and facial and body hair, muscle gain and fat redistribution continue to develop for up to three to five years.
- Terminology
- ATC G03BA03
- Monitoring
- Baseline bloods before starting: two morning testosterone levels, a full blood count, lipids, liver function and blood pressure, with a prostate examination in men. Testosterone and haematocrit are then checked at three to six months and yearly, PSA is repeated in men according to age and risk, and bone density is assessed after oophorectomy or if therapy is interrupted.
Availability by country
| Country | Status | Note | Source |
|---|---|---|---|
| UK | Controlled substance | UK |
Legal status differs between countries and can change; each row cites the document it was taken from and applies only to the country named.
What it is used for
- Male hypogonadism: testicular failure or pituitary disease confirmed by symptoms together with repeatedly low testosterone on morning samples, assessed by a specialist
- Delayed puberty in boys and induction of puberty in hypogonadal adolescents, under specialist care
- Gender-affirming masculinising hormone therapy for trans men and some non-binary people: an established use outside the product licence, started by a specialist service and often continued in primary care, and supported by the Endocrine Society and WPATH guidelines
- Low sexual desire in menopausal women when hormone replacement therapy alone has not helped, an unlicensed use that the NICE menopause guideline says can be considered
- Not for the gradual fall in testosterone with age in the absence of hypogonadism, for tiredness alone, or for muscle building and sport, where the harms of anabolic steroid misuse are well documented
How it works in the body
Testosterone enters cells and binds the androgen receptor, a nuclear receptor that alters gene expression over hours to days. 5-alpha-reductase converts it to the more potent dihydrotestosterone in prostate, skin and hair follicles, and aromatase converts some to oestradiol, through which it protects bone. It builds muscle, drives red cell production, sebum, body and facial hair, voice deepening and libido. As a medicine it also switches off LH and FSH, so sperm production falls and periods usually stop, though not reliably enough to be contraception.
Common side effects
- Acne and oily skin, increased body and facial hair, and thinning of scalp hair in those with a family tendency to male-pattern hair loss
- Mood change or irritability, weight gain, fluid retention, headache, and pain or bruising at injection sites or irritation under gel or patches
- In trans men and non-binary people: vaginal dryness and thinning (atrophy), which can be treated with a topical oestrogen, and cessation of periods, which is expected
Serious: seek help
- Erythrocytosis: a raised haemoglobin and haematocrit that thickens the blood and raises the risk of thrombosis, more common with injections; the dose or the interval between doses is adjusted if the haematocrit climbs
- Worsening of obstructive sleep apnoea and a rise in blood pressure
- Growth of the prostate with urinary symptoms and a rise in PSA; testosterone is not given to men with prostate cancer or male breast cancer
- Suppression of sperm production and shrinkage of the testes, reversible in most but not all cases; fertility preservation is discussed before starting
- Transfer of gel to partners or children through skin contact, which can virilise a child or the baby of a pregnant partner
- Liver damage with older oral (17-alkylated) androgens, and rarely a cough or breathlessness in the minutes after a long-acting oil-based injection
Cautions and interactions
- Contraindicated in prostate cancer, breast cancer in men, a history of primary liver tumours, hypercalcaemia, and in pregnancy and breastfeeding; not started in uncontrolled heart failure or untreated erythrocytosis
- Used with care in ischaemic heart disease, hypertension, epilepsy, migraine and kidney or liver disease because of fluid retention, and in sleep apnoea
- Enhances the effect of warfarin (INR is monitored) and may lower blood glucose in people taking insulin or other diabetes medicines
- After applying gel, wash the hands, cover the site and avoid skin contact with others until the skin has been washed
- In trans men and non-binary people testosterone is not contraception: ovulation can occur even when periods have stopped, and anyone with a cervix still needs cervical screening
- Anabolic steroid misuse for muscle building carries the same harms at higher doses: erythrocytosis, heart disease, liver injury, infertility and mood disturbance
Interactions
Check interactions
Taking Testosterone with other medicines? Add them to the checker to see what the official sources say about each pair: the mechanism, general management and monitoring, never a bare "safe".
Interactions documented in the official sources cited on each card. The list covers the medicines represented on this site and is not exhaustive; how the interaction data is compiled.
No pair records for this medicine are in the sources currently represented by Anatomy Nexus. Absence from this list does not mean no interaction exists.
Same-class and related medicines
Same class: Androgens
Medicines that share the class of Testosterone. They are separate medicines with their own licences, doses and interactions, not alternative names for Testosterone.
Related medicines
Medicines often discussed alongside Testosterone: used together, compared with it, or acting on the same problem by a different route.