Drug Treatment - Pilot's License

I've been assigned the task of finding out the consequences of a
private pilot who voluntarily checks into drug rehab for assistance
beating a cocaine addiction. There have been no arrests, convictions
or run-ins with the law of any kind. Could any of you direct me to
the regs (DOT/FAA regs? - sorry, I forget which, as I haven't flown in
years) or any other resources that definitively address this issue?

I would like to have this info available when an intervention is
conducted next week. Thanks,

Julia Ambrose