What is Testosterone?

Testosterone is a hormone produced naturally in the body. It is the major sex hormone in males and is produced in smaller quantities in the ovaries and adrenal glands of females.

Testosterone is also available as a prescription medication, belonging to the drug class of anabolic-androgenic steroids. This is a human-made (synthetic) form of testosterone and is designed to bring about the same effect as naturally occurring testosterone.

Some people also use testosterone illicitly, outside of a medical context.

What are the different forms of Testosterone?

Testosterone is available in a few different forms:



These are applied directly to the skin. It is possible for these gels to transfer to other people unintentionally if their skin touches the area which the gel has been applied to. 



Liquid testosterone designed to be injected deep into the gluteal muscle.



Transdermal patches which are applied to the skin. They are usually worn at all times and replaced with a new patch every 24 hours.


Oral tablets & Capsules

Methyltestosterone and testosterone undecanoate available for oral administration and can be used as an alternative to gels for androgen deficiency.  Prescribed to help bone growth in boys being treated for delayed puberty.



Other testosterone products:



Testosterone boosters are supplements which claim to increase levels of testosterone in the body. These are typically precursors to testosterone and are sometimes available in health shops. However, these can vary in quality and there is little scientific evidence to support their use.

How does Testosterone work as a drug in the body and brain?

Testosterone activates androgen receptors in various tissues in the body. This in turn leads to the expression of genes which cause growth and development of male sex organs and secondary sexual characteristics. For example, the thickening of vocal cords, which leads to deepening of the voice.

What are the effects of Testosterone?

Unlike some drugs, the effects of testosterone will not be seen in a matter of minutes or hours. Some effects, such as increased libido, can be seen after 3 weeks of use. However, other effects, such as changes in muscle strength, can take up to 16 weeks to be seen.  


The effects of testosterone include:


  • Development of male sex organs
  • Deepening of the voice
  • Growth of facial and pubic hair
  • Increased muscle size and strength
  • Bone growth and strength
  • Increased libido (sex drive)
  • Increased sperm production
  • Ovarian function

Does Testosterone have any medical uses?

Testosterone and its derivatives have various medical uses. It can be used to treat delayed male puberty and abnormally low production of testosterone. Testosterone therapy can also help with generalised weakness, low energy, disabling frailty, depression, problems with cognition and problems with sexual function.


Another medical use for testosterone is masculinising hormone therapy (or gender affirming therapy) for transgender men and non-binary people. This produces physical changes of secondary sex characteristics, helping to better align the body with gender identity. When used in this context, testosterone also stops the menstrual cycle and decreases oestrogen production in the ovaries.

What are the risks of using Testosterone? Can they be avoided or reduced?

Using testosterone involves some risks. The risks are increased when an artificially high level of testosterone is present in the body which is more likely to occur when testosterone is taken outside of a medical context.


These risks include:

  • Low sperm count
  • Heart damage and increased risk of cardiac arrest
  • Prostate enlargement
  • Liver disease
  • Insomnia
  • High blood pressure
  • High cholesterol
  • Increased risk of blood clots
  • Mood swings


The risk of experiencing these effects can be reduced by only taking the amount of testosterone you are prescribed. Illicit users should limit use to prevent these effects from occurring.

Are there health conditions that make Testosterone more dangerous?

Whilst using testosterone doesn’t increase the risk of developing prostate cancer, it can stimulate the growth of cancerous prostate cells. Therefore, those with prostate cancer or at risk of developing prostate cancer should not take testosterone.


Testosterone and testosterone-based products should not be used in men who have hypercalcemia (raised calcium) or a history of breast or liver cancer.

Can Testosterone be used with other drugs?

If testosterone is taken alongside an adrenocorticotropic hormone or corticosteroids, a build up of fluid (oedema) may occur in the body.

How addictive is Testosterone?

People who regularly use testosterone outside of a medical context are at risk of developing an addiction to the drug, both physical and psychological. Withdrawal symptoms are felt if the person ceases use or lowers the dose that they take.


Medical assistance should be consulted for help with testosterone addiction. Medical professionals can help to find a safe way to stop taking testosterone and help to minimise withdrawal symptoms.

What are the harms of Testosterone addiction and withdrawal?

As with any addiction, addiction to testosterone can lead to problems at work or school and put a strain on personal relationships, alongside the physical and mental health issues that can ensue.  


Withdrawal symptoms include:

  • low libido
  • loss of appetite
  • mood swings
  • insomnia
  • fatigue
  • depression


Some signs that a person may be addicted to testosterone include:

  • Ignoring responsibilities
  • Persistent issues with friends and family
  • Continuing to use testosterone despite negative physical side effects.
  • Spending a lot of time and money in an effort to obtain testosterone.
  • Struggling to cut back on use despite repeated attempts.

Testosterone harm reduction advice

Minimising use, avoiding addiction

Physical dependence to testosterone does not occur immediately, however, the effects produced are often desirable for those who chose to use it. Therefore, they are likely to continue to use testosterone to increase the effects. This results in tolerance developing and a higher dose being required to produce desired effects. If you use testosterone illicitly, try to limit the dose you take and how often you take it.


How are you taking it?

Injecting any substance carries an increased risk of infection. If injecting, use new, sterile equipment. Do not re-use equipment and dispose of needles in a sharps bin. These are available from your local pharmacy and do not require a prescription.


Using an oral or topical form (creams or gels) of testosterone minimises the risk of infection. If using topical steroids, wash hands with soap immediately after use.