Several methods of prevention are currently in use across professional sports. The most common preventative measure is drug testing.
By testing athletes on both regularly and at random times, professional sports bodies attempt to catch any illegal performance enhancing doping.
Sports like the NFL and NBA have defined penalties for abuses of substance abuse policies. These penalties are the deterrents intended to stop athletes from doping. Penalties, to date, do not include expulsion from the sport, though this is serious deterrent may one day be implemented.
What these sports currently seem to lack is a policy regarding record-keeping. This has been very clear in Major League Baseball, a sport recently marked by the dilemma of how to deal with home run records set by players guilty of using performance enhancing drugs.