Morphine/Codeine Ratio, a Key in Investigating a Case of Doping

Consumption of codeine can lead to positive urine test for morphine in athletes. Morphine is classified as a prohibited doping drug while Codeine is not. Morphine/codeine ratio is used in forensic medicine to distinguish the consumption of codeine from abuse of morphine and other narcotics. We present an athlete with positive urine test for morphine with a history of consumption of codeine. The disciplinary committee came to conclusion that the athlete had not consumed morphine and did not violate doping code based on morphine/codeine ratio. Analysis of codeine to morphine metabolism rate is needed when we are using morphine/codeine ratio to rule out abuse of narcotics. WADA should consider analysis for the CYP2D6 alleles (main metabolizer of codeine) in case of including morphine/codeine ratio in future prohibited list. The possibility of ultra-rapid CYP2D6 cannot be ruled out in certain results of morphine/codeine near the cut point.