We examine the impact of regulation on the doping decisions of athletes in a Tullock contest. The regulatory measures we consider are greater monitoring by sports authorities and a lowering of the prize in the contest. When legal efforts and illegal drugs are substitutes, an increase in anti-doping regulation may, counterintuitively, increase the levels of doping activity by athletes. Anti-doping regulation can also have the undesirable consequence of decreasing legal efforts; in our model, this always occurs when legal efforts and illegal drugs are complements, and under certain circumstances when they are substitutes.