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

INTRODUCTION: 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. CASE PRESENTATION: 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. CONCLUSIONS: 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.