Judo fighter Nick Delpopolo, who was disqualified from the Olympics on Monday, said the cannabis in his system came from something he ate that he didn't know contained marijuana—an all-too-plausible excuse that makes his situation all the more disappointing. Compounding that disappointment is marijuana's debatable role as a performance enhancing drug.

While a few reports have cited "pot brownies," we haven't seen one that quotes the New Jersey native saying what he actually ate. A pot brownie (or cookie or rice cake or whatever) normally wouldn't do much harm to a healthy 23-year-old, but in this case it winds up having him stripped of his seventh-place Judo finish. The scenario of a send-off party and a plate of innocuous-looking deserts, is easy enough to imagine, but all Delpopolo said was in a statement quoted by AP and others: "I apologize to the U.S. Olympic Committee, to my teammates, and to my fans, and I am embarrassed by this mistake. I look forward to representing my country in the future, and will re-dedicate myself to being the best judo athlete that I can be." 

That marijuana even occupies a place on the World Anti-Doping Agency's list of banned substances is a matter of no little debate. The Australian Coalition of Major Professional and Participation Sports is lobbying to have it removed, and Reuters reports that WADA president John Fahey has said the organization might change its criteria for banning the substance, but not this year. The current criteria include: "It is proven to be performance enhancing, it goes against the spirit of sport, or it is dangerous to the health of athletes," per Reuters. In a report for ESPN Dr. Gary Wadler, a New York University School of Medicine professor and lead author of the book Drugs and the Athlete, argued that the drug had no performance enhancing characteristics. Though Reuters notes that "some experts say it could prove helpful in sports like shooting or golf where a steady hand is needed."

The problem with pot is that it can stay in the body's fat, making for a positive result for up to four weeks after use, Wadler notes. So, while it's hard to prove pot's effectiveness as a performance enhancer, it's easy to prove its presence.