This year’s fastest sprinters, Tyson Gay and Asafa Powell, have tested positive for the banned amphetamine.

Tyson Gay and Asafa Powell, the two fastest sprinters in the world this year, have both tested positive for the banned amphetamine oxilofrine. Both have insisted they are not cheats. Here’s our guide to the banned substance.

What is oxilofrine?

Oxilofrine is a stimulant drug of the amphetamine class that was developed and used to treat hypotension (low blood pressure) in people who do not respond to conventional treatment.

Oxilofrine is the prescription name for methylsynephrine, hydroxyephrine, and oxyephrine. It is not widely used in the UK and is not a licensed drug in the US.

Some companies use oxilofrine, in the form of synephrine, in “sports nutritional supplements” as it is thought to allow people to enhance fat-burning and lose weight.

Synephrine is present as a natural component of Citrus aurantium, otherwise known as “bitter orange”, but it can also be synthesised artificially or extracted from plant sources and purified.

What are its effects?

Oxilofrine is thought to give a sporting edge by increasing the production of adrenaline, so boosting exercise endurance, focus, alertness and heart rate, and increasing oxygenation of the blood.

Is it dangerous?

Continued long-term abuse of a drug such as oxilofrine could put someone at risk of tachycardias (very high heart rate), cardiac dysrhythmia (irregular heartbeat) and haemorrhagic stroke. It can also cause hypertension (high blood pressure) if taken by people with normal blood pressure.

How do you take it?

If not supplied on prescription, then oxilofrine (methylsynephrine) would most commonly be taken as a sports nutrition supplement, mixed with other supplements, in liquid capsule form.

Why is it banned?

Oxilofrine is banned because it is considered a performance-enhancing drug. Oxilofrine is on the World Anti-Doping Agency’s (WADA) list of banned substances.

What does WADA say?

Oxilofrine is a banned substance by WADA and is found in “stimulants: section S6” in section “b: specified stimulants”.

WADA states: “A specified substance is a substance which allows, under defined conditions, for a greater reduction of a two-year sanction when an athlete tests positive for that particular substance.” It goes on to say: “Specified substances are not necessarily less serious agents for the purpose of doping than other prohibited substances, and nor do they relieve athletes of the strict liability rule that makes them responsible for all substances that enter his or her body. However, there is a greater likelihood that these substances could be susceptible to a credible non-doping explanation, as outlined in section 10.4 of the World Anti-Doping Code.”