Athletics suffered one of its darkest days following revelations this week that two of the world's fastest men, Tyson Gay and Asafa Powell were among six athletes to have tested positive for banned substances.

Gay and Powell both aged 30, and Jamaican woman sprinter Sherone Simpson who was part of the gold medal-winning quartet at the Athens Games and a silver medallist at the London Games last year were found to have an illegal product in their systems in an out-of-competition drug test in May.

Drugs have provided the world of athletics with a fierce opponent ever since the emergence of systematic forms of doping in the former Eastern Europe, with Kenya being one of the places where the news reverberated like a booming echo.

Elizabeth Odera, a sports medicine specialist, told Xinhua that the list of banned substances was so comprehensive that it was highly unlikely that an athlete could take a legal substance but register a positive result in a doping test.

"However, there are two areas that could catch athletes out. Some cough and cold remedies include banned stimulants such as ephedrine and pseudo-ephedrine."

However, she says, athletes are usually warned about the risks associated with taking such medications without first checking the ingredients.

Odera says the other area where athletes could be caught flat-footed lies in herbal remedy, some of which she says contain banned substances.

"The problem with many herbal drinks is that they do not provide an exhaustive list of contents."

British sprinter Linford Christie was cleared of wrongdoing despite failing a drugs test when it was discovered he had drunk ginseng tea.

Athletes are banned from taking thousands of chemical substances that experts believe will give them an unfair advantage.

There are five main categories of drugs that are banned; anabolic steroids, peptide hormones, strong analgesic painkillers, stimulants and diuretics.

In addition to the five main categories, there are other types of drugs that are subject to restrictions on their use.

These include local anesthetics and drugs used to treat medical conditions such as cortico-steroids, which are used to treat asthma; and beta-blockers which are used in the treatment of heart conditions.

Not since the disgraced Canadian sprinter Ben Johnson tested positive of anabolic steroids during the 1988 Seoul Olympics has the drug menace received unprecedented global attention.

Johnson tested positive just hours after setting the 100m world record in a time of 9.79 seconds but was immediately stripped of the medal and the record nullified after which he was slapped with a four-year ban.

Odera says that if a positive test is found, two things are likely to have happened; either the athlete has taken a banned substance by mistake in an over-the-counter medicine, or they have taken a substance which they could have got hold of illegally.

"If the latter is the case, then they have either taken it knowingly, or somebody has given it to them without their knowledge. However, quite a lot of these substances have to be taken by injection so it is very unlikely they will know nothing about it."

Athletics Kenya vice president Paul Mutwii concurs it is highly unlikely for an athlete to take substances like anabolic steroids by 'mistake' but adds that there is a "grey area" over some of the banned substances.

"So many of the medicines administered for coughs and colds contain stimulants such as ephedrine that a young and inexperienced athlete might naively take in this way, thinking it was perfectly alright."

Mutwii says this is the predicament Kenyan athletes who have tested positive for banned substances have found themselves in owing to their disadvantaged backgrounds and modest education.

"It is instructive to note that those Kenyan athletes who have found themselves on the wrong side of the anti-doping laws owing to having used over-the-counter medication that contained a banned substance are those whose careers are still fledgling and the veterans.

"However, I would be surprised if an experienced athlete did that because they know how vigilant they need to be."

During a dope test, an athlete accompanied by a chaperone and his/her manager, goes to the drug control area.

Here the athlete is supplied with drinks and asked to give a urine sample, still accompanied by the chaperone.

The sample is then split into two. Sample A is tested first, sample B is only tested if A proves positive.

The World Anti-Doping Agency (WADA) has been calling on governments and sporting bodies to treat seriously the threat to sports posed by drug cheats.