How is doping tested in sport?

Through a combination of urine and blood samples, collected both at competitions and without warning out of competition, analysed against a prohibited list maintained by the World Anti-Doping Agency.

The WADA Prohibited List is updated annually and covers substances and methods banned at all times, and some banned only in competition. A substance is generally included if it meets two of three criteria: performance enhancement, health risk, or contrary to the spirit of sport.

Out-of-competition testing is the part that does most of the work. Many banned substances confer benefits during training and clear the body before an event, so testing only at competitions would miss them. Athletes in registered testing pools must file their whereabouts — where they can be found for one hour each day — and missed tests count as violations. Three within twelve months is treated as a positive.

Sample collection is closely observed to prevent substitution, and each sample is split into an A sample and a B sample. If the A sample tests positive, the athlete may request analysis of the B sample, which must confirm it.

The Athlete Biological Passport takes a different approach: rather than looking for a substance, it tracks an individual's blood and steroid markers over time and flags changes that are physiologically implausible without intervention. This can catch doping methods for which no direct test exists.

Strict liability applies. An athlete is responsible for what is in their body regardless of intent, which is why contaminated supplements are a recurring cause of bans.

Samples are now stored for up to ten years and can be re-analysed as detection methods improve — several Olympic medals have been reallocated years later.