Steroids 'kill off brain cells'
Using steroids to build bulging muscles can also trigger "catastrophic" loss of brain cells, research suggests.
The drugs are known to raise levels of the male sex hormone testosterone.
A study published in the Journal of Biological Chemistry by Yale School of Medicine found high levels of the hormone killed off nerve cells.
The researchers believe the effect might explain why some steroid users become aggressive and suicidal - a condition known as hyperexcitability.
[Steroids] are known to have a major negative effect on people's health
The condition is well known in the bodybuilding world, where it is referred to as roid rage.
Lead researcher Professor Barbara Ehrlich said: "Next time a muscle-bound guy in a sports car cuts you off on the highway, don't get mad, just take a deep breath and realise that it might not be his fault."
The Yale team exposed cultured nerve cells to testosterone, and found that it triggered programmed cell death (apoptosis).
This is a natural process that in normal circumstances plays a key role in clearing away damaged cells which might be harmful.
However, when healthy cells also become suicidal, it can cause severe problems, and has been implicated in neurological illnesses, such as Alzheimer's and Huntingdon's disease.
Apoptosis is characterised by membrane instability, DNA fragmentation, and the activation of "executioner proteins", known as caspases.
A recent US study published in the journal Behavioural Neuroscience found normally placid adolescent hamsters given anabolic steroids become incredibly aggressive.
The effects lasted almost two weeks - the equivalent of half their adolescence.
Post-mortems revealed changes in the hamsters' brain activity.
Dr Richard Melloni, who led the research at Northeastern University in Boston, said it was likely the findings applied to humans.
John Brewer, director of the Lucozade Sports Science Academy, said the findings were not surprising.
"People think steroids are banned because they are performance enhancing, but the second, equally important, reason is that they are known to have a major negative effect on people's health.
"This study provides further evidence for why we should never give in to people who want to use steroids and drugs in sport. The moment we do that we will have a major hit on the health services, as use will cascade down the pyramid of sports."