The activity of the CYP450 enzymes responsible for the phase I metabolism of most of the compounds included in the World Anti-Doping Agency (WADA) list of prohibited substances and methods could be strongly modified by the combined administration of other drugs such as, for example, the antidepressant, the antifungal and the H2 receptor antagonist agents. These compounds act as inhibitors of the CYP450 isoforms and it has been demonstrated that their co-administration with a drug that is also a CYP450 substrate may lead to a substantial alteration of the latter drug bioavailability, metabolism and excretion kinetics. In sports some classes of non-banned drugs, and primarily among them antidepressants, antifungals and the H2 receptor antagonists are extensively used, according to the information available on the doping control forms. Athletes may intentionally combine the CYP450 inhibitors with doping agents to modify in urine the time window of detection of the selected marker(s) of drug abuse, especially in those cases where the parent drugs are extensively metabolized
