The first Olympic disqualification for drug use was against a Swedish pentathlete Hans-Gunnar Liljenwall who drank two beers before his shooting event to calm his nerves during the 1968 Olympics.
Hans-Gunnar Liljenwall, Tiny Fox Lab

Hans-Gunnar Liljenwall, Swedish modern pentathlete, was the first athlete to ever be disqualified for doping in the Olympics. He drank “two beers” to calm his nerves before pistol shooting, giving him an unfair advantage.Tiny Fox Lab Facts

Preview photo credit: Hans-Gunnar Liljenwall, Tiny Fox Lab