Anabolic steroids are synthetically produced chemicals that mimic the effects of natural hormones, especially the male sex hormones (androgens). They include drugs such as nandrolone and stanozolol.

Anabolic steroids help to build body tissue. They increase muscle development, particularly in the upper part of the body - the neck, shoulders, chest and arm muscles.

They also increase bone density while stopping growth at the ends of the bones. It's the production of these sorts of hormones in puberty that stops growth, which is one reason why we don't carry on growing taller through adult life.

Serious risks

The risks of anabolic steroids are well known. They include:

• Cardiovascular changes, such as atherosclerosis (hardening of the arteries) and an increased risk of heart attack
• Altering the ratio of good and bad cholesterol in the blood, lowering levels of the good high-density lipoprotein (HDL) and increasing levels of the bad low-density lipoprotein (LDL)
• Fluid retention, which puts additional strain on the heart
• Liver damage
• Increased risk of certain cancers, such as kidney and liver cancers
• Reduced fertility
• Acne
• Hair loss

Psychological changes are also possible. Although many people say they feel good on steroids, research from Harvard University shows mood swings, aggression, depression, paranoia and delusion are also possible.

Rarely used in medicine

Because of these potentially serious side effects, anabolic steroids are rarely used in medicine.

Occasionally, they're prescribed alongside a high-protein diet to help someone recover and build themselves up after a major and prolonged illness or operation.

They also have a few more unusual uses, such as in certain forms of anaemia to increase the production of red blood cells.

Misuse in sport

Anabolic steroids have been used (or abused) in many sports for years because they help to build muscle and strength. They also speed up the recovery of the muscles after a period of intense exercise, allowing athletes to follow a more demanding programme and greatly increase muscle power. Some say they also increase confidence and give a feeling of invincibility.

However, the bottom line is that the use of anabolic steroids in sport is illegal and a form of cheating. Most professional sporting bodies are clear in their condemnation of those who use steroids.

This article was last medically reviewed by Dr Trisha Macnair in October 2007