On Sunday, a British tabloid published a November photo of Olympic champion Michael Phelps smoking a bong. Fortunately for Phelps, the World Anti-Doping Agency prohibits marijuana only during competition periods. How does a drug make it onto WADA's list of banned substances?
It gets approved by three committees in consultation with 1,700 governments and sports-governing bodies. The WADA list is updated annually. First, the WADA List Committee, composed of 12 toxicologists, pharmacists, lab directors, and physicians, evaluates substances that might be banned. To be considered, a substance must satisfy two of three criteria: the potential to enhance performance; significant risk to the athlete; and contravention of the spirit of sport (meaning it is illegal or could be construed as cheating). Once two criteria are satisfied, the committee considers other factors, including ubiquity, usage trends, commercial availability, and whether the substance is detectable. (Caffeine, for example, used to be on the list but was removed because it became too difficult for WADA to police and for the athletes to avoid.) No single factor is decisive. Certain substances have been banned before laboratory tests could detect them, while in other cases the List Committee waited for reliable tests to emerge.
Once the List Committee decides what substances should be newly banned, it circulates its list to 1,700 governments and sports-governing bodies for comment. After reviewing any comments, the committee submits the list to the WADA Health, Medical, and Research Committee. If that committee approves the list, it must then be approved by the WADA Executive Committee. The two reviewing committees have the authority to make changes without further review by the List Committee. The revised list must be approved in October, but it takes effect in January so that athletes have an opportunity to adapt to rule changes.
The current list (PDF) contains three categories: substances or methods prohibited at all times (such as steroids and blood doping), substances prohibited during competition periods (including stimulants like methamphetamine), and substances prohibited for particular sports (no alcohol in auto racing or, oddly, bowling).
Marijuana, which has been on the WADA list since the first draft in 2003, is prohibited because it poses a danger to the athlete and is illegal in most jurisdictions. It is, however, something of a special case among substances prohibited only during competition. Unlike stimulants or asthma drugs, there isn't much evidence that pot enhances performance, no matter when it is used. The List Committee likely declined to prohibit it year-round because of its ubiquity in many countries.
An athlete with a condition requiring use of a banned substance can petition WADA for a therapeutic-use exemption. The petitioner must prove that 1) she has a medical condition and 2) there is no efficacious alternative to the banned substance. No athlete has sought a medicinal-marijuana exemption, but the petition would probably fail the second test.
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Explainer thanks Gary I. Wadler of the World Anti-Doping Agency.