[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Androgens](https://durgical.com/en/pharmacology/classes/androgens/) › Testosterone

# Testosterone

## Androgens?

Androgens

## Pregnancy: contraindicated?

Contraindicated in pregnancy: it can virilise a female fetus.

The main male sex hormone, given as injections, gels or patches to replace testosterone in men whose testes or pituitary do not make enough.

Updated Nov 1, 2026

Also called: Testosterone cypionate, Testosterone enanthate, Testosterone undecanoate

## Quick facts

**Group**
[Androgens](https://durgical.com/en/pharmacology/classes/androgens/)

**Target**
Androgen receptor (AR), a nuclear receptor

**Used for**
Primary hypogonadism · Testicular failure

**Key effects**
Acne and oily skin · Injection-site pain · Mood swings

**Monitor**
Haemoglobin and haematocrit · Testosterone levels

**ATC**
G03BA03

No doses: the clinician sets them by the current guideline.

On this page

- The basics Mechanism of action
- Indications
- Adverse effects
- Pharmacokinetics
- Memory aid

- Clinical What the labels mean

- Safety Contraindications
- Key interactions
- What is monitored
- Administration and safety
- Pregnancy and breastfeeding
- Nursing care

- Study Test yourself

- Connections Connections

## Mechanism of action

◎**Androgen receptor (AR), a nuclear receptor**Testosterone

ⓘ The figure shows testosterone itself in the ligand-binding domain of the human androgen receptor.

**Target in 3D:** Androgen receptor (AR), a nuclear receptor. PDB structure 2AM9 (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/2AM9) · Drag to rotate · pinch to zoom

Testosterone binds the androgen receptor directly and, after conversion by 5-α-reductase, as dihydrotestosterone; part is aromatised to estradiol. In hypogonadal men it restores libido, erections, secondary sexual characteristics, muscle, bone density and red-cell production. Through negative feedback it suppresses LH and FSH, so the testes make less of their own testosterone and sperm.

- Testosterone reaches target tissues and enters the cells
- It binds the androgen receptor directly or as DHT
- Androgen-dependent genes switch on in muscle, bone, skin and genitals
- LH and FSH fall, lowering sperm production

## Indications

- Primary hypogonadism (testicular failure: e.g. cryptorchidism, orchidectomy, Klinefelter syndrome) [Male hypogonadism →](https://durgical.com/en/conditions/male-hypogonadism/)
- Testicular failure in Klinefelter syndrome [Klinefelter syndrome (47,XXY) →](https://durgical.com/en/conditions/klinefelter-syndrome/)
- Hypogonadotropic hypogonadism (pituitary or hypothalamic deficiency) [Male hypogonadism →](https://durgical.com/en/conditions/male-hypogonadism/)
- Delayed puberty in boys

## Adverse effects

### Common

- Acne and oily skin
- Injection-site pain
- Gynaecomastia
- Mood swings, sleep problems
- Fluid retention and weight gain

### Serious (rare, important)

- Erythrocytosis (high haematocrit)
- Venous thromboembolism
- Worsening of BPH with urinary obstruction; possible growth of prostate cancer
- Raised blood pressure and possible cardiovascular events
- Suppressed spermatogenesis
- Abuse: heart, liver and psychiatric harm; liver tumours with high doses

## Contraindications

- Breast cancer in men
- Known or suspected prostate cancer
- Pregnancy (it virilises a female fetus)
- Serious cardiac, liver or kidney disease
- Hypersensitivity to the drug

## Key interactions

**Oral anticoagulants (warfarin)**
Greater anticoagulant sensitivity; INR is watched and the anticoagulant dose may need reducing

**Insulin and other antidiabetics**
Insulin requirements may fall in people with diabetes

## What is monitored

- Haemoglobin and haematocrit
- Testosterone levels
- Blood pressure
- Prostate symptoms (and PSA as clinically indicated)
- Lipids and liver tests; bone age in boys with delayed puberty

## Administration and safety

- The cypionate and enanthate injections are deep intramuscular (gluteal) and never intravenous
- Some products are given only in a health facility with observation afterwards because of a risk of breathing problems or allergy
- Injectable, gel and patch products are not interchangeable without an order
- Testosterone is a controlled substance and is not shared

## Pregnancy and breastfeeding

Contraindicated in pregnancy: it can virilise a female fetus.

## Nursing care

- Check haematocrit and blood pressure before and during treatment
- Teach to report leg pain or swelling, chest pain or sudden breathlessness
- Ask about urinary symptoms and sleep apnoea
- Explain that it lowers sperm count and is not a fertility treatment
- Teach safe storage and that it must not be shared or used at higher doses

## Pharmacokinetics

**Absorption**
Injected as long-acting esters into muscle (some under the skin), or absorbed through the skin from gels and patches

**Distribution**
Mostly bound to SHBG and albumin

**Metabolism**
In the liver; converted in tissues to DHT and estradiol

**Elimination**
As conjugated metabolites in urine

## Memory aid

Testosterone watch list = «PACT»: Polycythaemia, Acne, Clots, Testes make less sperm.

## Test yourself

Think of the answer, then tap the question to see it.

## Why can testosterone therapy cause infertility?

It suppresses LH and FSH by negative feedback, so the testes make less sperm.

## What must be checked regularly in a man on testosterone injections?

Haemoglobin and haematocrit for erythrocytosis, plus blood pressure, prostate symptoms and testosterone levels.

## Why is testosterone cypionate never given intravenously?

It is an oily depot meant for deep intramuscular injection; the label states it is not for intravenous use.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/testosterone/)

[More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology)

## What the labels mean

**Pregnancy: contraindicated**
Contraindicated in pregnancy: it can virilise a female fetus.

## Connections

## Related drugs 2

- [Danazol](https://durgical.com/en/pharmacology/danazol/)
- [Finasteride](https://durgical.com/en/pharmacology/finasteride/)

## Related conditions 2

- [Male hypogonadism](https://durgical.com/en/conditions/male-hypogonadism/)
- [Klinefelter syndrome (47,XXY)](https://durgical.com/en/conditions/klinefelter-syndrome/)

[← Back to the class: Androgens](https://durgical.com/en/pharmacology/classes/androgens/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [DailyMed - TESTOSTERONE CYPIONATE injection](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=78d55bad-4a5b-4e21-aeb8-a4c6346208be) (DailyMed (U.S. National Library of Medicine), 2026); [Testosterone Injection: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a614041.html) (MedlinePlus (U.S. National Library of Medicine), 2025); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=G03BA03) (WHO Collaborating Centre for Drug Statistics Methodology, 2026); [eEML - Electronic Essential Medicines List](https://list.essentialmeds.org/) (World Health Organization, 2025).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/pharmacology/testosterone/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/testosterone/