Testosterone (TRT) — NZ Medication Guide
📋 Reviewed by a Registered Pharmacist NZ — This information is for general educational purposes only and does not replace professional medical advice. Always consult your doctor or pharmacist before starting, stopping, or changing any medication.
What is Testosterone (TRT)?
Testosterone is the primary male sex hormone used as testosterone replacement therapy (TRT) for hypogonadism. This medication is funded by Pharmac under Special Authority for confirmed hypogonadism.
What is Testosterone (TRT) Used For?
Used for male hypogonadism (insufficient testosterone production) — treating fatigue, reduced libido, erectile dysfunction, low mood, loss of muscle mass, and osteoporosis.
How Does Testosterone (TRT) Work?
Testosterone binds to androgen receptors in target tissues, maintaining male sex characteristics, bone density, muscle mass, libido, erythropoiesis, and cognitive function.
How to Take Testosterone (TRT)
Available as IM injection (testosterone enanthate every 2–4 weeks; testosterone undecanoate every 10–14 weeks), transdermal gel (Testogel® — applied daily), and implants. Regular monitoring of testosterone levels, haematocrit, and PSA required.
Common Side Effects of Testosterone (TRT)
- Acne and oily skin
- Fluid retention
- Polycythaemia (elevated red blood cells)
- Mood changes
- Testicular atrophy
- Infertility (reduced sperm production)
Serious Side Effects — Seek Medical Attention
Contact your doctor or call 111 immediately if you experience any of the following:
- Polycythaemia (elevated haematocrit — increases thromboembolism risk — monitor FBC)
- Prostate cancer acceleration (contraindicated in prostate cancer)
- Sleep apnoea worsening
- Cardiovascular events (evidence debated)
Drug Interactions
Testosterone (TRT) may interact with other medicines. Always inform your doctor and pharmacist of all medications you are taking. Key interactions include:
- Warfarin (may increase anticoagulant effect — monitor INR)
- Insulin and antidiabetics (may increase insulin sensitivity)
New Zealand Prescribing Information
Testosterone enanthate (Primoteston Depot® 250 mg/mL), testosterone undecanoate (Nebido® 1000 mg/4 mL), and Testogel® 50 mg/5 g gel sachets are funded under Special Authority for confirmed male hypogonadism. Two morning testosterone levels below reference range with symptoms are required for diagnosis. Testosterone does not restore fertility — gonadotrophin therapy is used for fertility goals.
Frequently Asked Questions
Will TRT affect my fertility?
Yes — TRT suppresses LH/FSH, reducing sperm production and typically causing infertility during treatment. Men wishing to father children should discuss fertility preservation or gonadotrophin therapy before starting TRT.
How is testosterone deficiency diagnosed?
Two separate early morning (8–10 am) testosterone measurements below the laboratory reference range, with symptoms of hypogonadism, are required for diagnosis. A single low level is insufficient.
References & Further Information
The following New Zealand and international resources were used to inform this page:
- New Zealand Formulary — Testosterone
- Pharmac — Funded Medicines Schedule
- Endocrine Society Hypogonadism Guideline
⚠️ Disclaimer: This page is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your doctor or a qualified health provider. In New Zealand, medication availability and funding may vary — check with Pharmac or your pharmacist for current information.
Reviewed by a Registered Pharmacist NZ