The World Anti-Doping Agency, who defines what a performance enhancing drug is and if it's banned in sports, grants Therapeutic Use Exemptions for methylphenidate and its siblings. This is despite some countries using other medicines as first-line treatment for ADHD that aren't banned by WADA.
The justification is that treatment for people with ADHD markedly reduces accidents and suicidality, and that banning the drug outright would do more harm than would come from liars getting the drug and harming sports.
The justification is that treatment for people with ADHD markedly reduces accidents and suicidality, and that banning the drug outright would do more harm than would come from liars getting the drug and harming sports.