Tennis player Greg Rusedski tested positive for the banned substance nandrolone, but was found not guity of doping.
So what is nandrolone, and how is it detected in the human body?
Are tests for nandrolone conclusive?
Even though a drug test may indicate that the subject has apparently taken nandrolone to boost muscle growth and increase strength, this does not necessarily prove wrongdoing.
It is possible that the body may naturally create a form of nandrolone, particularly if the subject has eaten large quantities of meat contaminated with the substance.
Certain animals may create a bigger risk, particularly horse and boar - and athletes are warned to avoid offal from these animals.
It is also possible that dietary supplements which appear perfectly legal can be broken down by the body to produce the same substances created when nandrolone is broken down.
Again, athletes are warned not to believe everything they read on the labels of these supplements.
A UK Sport report on nandrolone said: "We recommend that the sports community should be reminded they must maintain a high level of awareness of the possible hazards of using some nutritional supplements and herbal preparations".
The other source of nandrolone metabolites is other types of steroid - but these are also banned by world sport bodies.
What are anabolic steroids?
Anabolic steroids are drugs that are usually synthesised from the male reproduction hormone testoterone.
They have been banned by many sports because of their danger to health.
Their exact effect on the body is still a matter of scientific debate.
Why do sportsmen take them?
Anabolic steroids can improve the body's capacity to train and compete at the highest level.
They reduce the fatigue associated with training, and the time required to recover after physical exertion.
They also promote the development of muscle tissue in the body, with an associated increase in strength and power. This is achieved by stimulating the production of protein in the body.
However, some of the increased muscle bulk may be due to the laying down of water and minerals, so the increase in strength may not be as pronounced as expected.
What are the risks associated with anabolic steroids?
Anabolic steroids promote the growth of many tissues in the body by stimulating the release of the hormone testoterone.
By disturbing the body's equilibrium, anabolic steroids can potentially cause damage to many of the body's major organs, particularly the liver, which has to deal with breaking down the compound.
There is also a significant risk of damage to the heart, which is made of muscle tissue. Anabolic steroids can lead to an expansion of the cardiac muscle, which can cause heart attacks.
The drugs also promote the growth of bones, particularly facial bones such as the jaw, and the teeth.
There is also an increased risk of cancer.
Other side effects include:
- The development of inappropriate sexual characteristics such as breasts in men, and facial hair in women;
- A deepening of the voice;
- Male impotence.
John Brewer, director of the Human Performance Centre at the Lilleshall National Sports Centre, said: "The health risks associated with anabolic steroids are as serious as you can get.
"They greatly increase a person's risk of dying early or of suffering long-term physical problems.
"While the rewards of success in sport are getting greater and greater, the temptation to take anabolic steroids should be offset by the risk of an early grave."
Are all anabolic steroids detected by drugs tests?
Some sports people who take anabolic steroids escape detection because they stop taking the drugs prior to competition, giving the body time to break down the compounds.