Testosterone replacement therapy

Testosterone replacement therapy (TRT) is a medication prescribed by a doctor to treat low testosterone levels in men.

Key points

  1. Testosterone replacement therapy (TRT) is a medicine to treat the symptoms of testosterone deficiency (low testosterone levels), a condition called hypogonadism.
  2. TRT is not the same as anabolic steroids or performance-enhancing steroids, which are unregulated. Long-term use of these steroids can cause harm.
  3. In some men with low testosterone, TRT can improve your mood, energy, wellbeing, libido and sexual function.

What is testosterone replacement therapy?

Testosterone replacement therapy (TRT) is testosterone given as a medicine prescribed by a doctor to treat the symptoms of low testosterone levels. It comes as a patch (Androderm), injection (Depo-Testosterone, Sustanon 250, Reandron) or capsules (Andriol). 

TRT is not for everyone. You will need to have blood tests and a full discussion with your doctor to see if it is right for you. Read more about low testosterone levels.

What is the difference between TRT and performance-enhancing or anabolic steroids?

TRT is a medicine prescribed by your doctor to treat testosterone deficiency and reach physiologic (natural) levels of the hormone in your blood.

Anabolic steroids or performance-enhancing steroids are unregulated products that contain testosterone or chemicals that act like testosterone. They are sometimes used by bodybuilders and athletes. They contain these substances in higher doses and these are often combined with other chemicals that boost the overall muscle-building (anabolic) effect.

Long-term use of anabolic steroids or performance-enhancing steroids can cause harmful effects.

What should I know about the different TRT options?

  • Injection: The TRT injection can cause swings in testosterone levels in some people which can lead to fluctuations in mood, sexual behaviour, breast tenderness and other symptoms. You will need to have follow- up blood tests – make sure you have these on time, to check the dose is right for you. Before injecting, warm the medicine to body temperature to reduce pain at the injection site. It is important that Reandron is injected slowly into a large muscle. 
  • Patch: You should avoid showering, swimming and sexual activity for 4 hours after putting on the patch. Skin irritation is common at the site of the patch.
  • Capsules: These are best taken with food.

When is TRT used?

TRT is used to treat testosterone deficiency (low testosterone) in some men. A low testosterone level by itself doesn't need treatment. TRT can have side effects, and the long-term risks and benefits aren't well known. 

Only men with symptoms of low testosterone and blood tests that confirm this should consider testosterone replacement. Men with testosterone levels in the bottom of the normal range (ie, still normal) are generally not treated with TRT. Read more about low testosterone levels.

What are the benefits of TRT?

The benefits of testosterone treatment can include improved mood, such as feeling less depressed, an overall feeling of energy and wellbeing, and improved libido and sexual function. TRT can also change your body composition, eg, give you more muscle mass and less abdominal fat.

Is TRT used for erectile dysfunction?

If erectile dysfunction is the only symptom of low testosterone, TRT is unlikely to be used. A PDE5 inhibitor such as sildenafil is preferred, after other causes have been addressed. Read more about erectile dysfunction and PDE5 inhibitors.

When is TRT not suitable?

TRT is should not be used if you have:

  • known or suspected breast or prostate cancer
  • liver tumours
  • high calcium levels (hypercalcaemia)
  • severe heart or kidney disease
  • untreated sleep apnoea.

What are the side effects of TRT?

Possible risks of testosterone treatment include:

  • decreased sperm production (if you want to improve your fertility, you should not use testosterone therapy)
  • a high red blood cell count, which can cause heart problems and blood clots
  • acne and oily skin
  • worsening of male pattern baldness
  • an increase in prostate size
  • unmasking or worsening of a pre-existing prostate cancer (but it doesn’t cause prostate cancer)
  • skin irritation of the area of the patch
  • pulmonary oil microemoblism for Reandron injection (spread of oil droplets into your lungs)
  • testicular (ball) shrinkage on rare occasions with injections.

Can you boost low testosterone naturally?

The following lifestyle changes can help you maintain a healthy level of testosterone:

  • lose weight if you are overweight
  • keep active and exercise regularly (but not vigorously)
  • get enough sleep (at least 7 hours per night)
  • don't drink too much alcohol
  • reduce stress. 

Do not use anabolic steroids.


  1. Prescribing testosterone in ageing males – why you shouldn’t read this article BPAC, NZ, 2015
  2. Testosterone deficiency in men Auckland Regional HealthPathways NZ, 2020
Credits: Sandra Ponon, Pharmacist. Reviewed By: Dr Jeremy Steinberg, FRNZCGP and Angela Lambie, Pharmacist, Auckland Last reviewed: 22 Jun 2020