What the heck does this have to do with legalization? Your employee's performance was presumably suffering because of their addiction, and in any event, theft from your employer is grounds for dismissal.
Your employee was not any less addicted due to the criminalization of drugs.
Meth is extremely addictive and should be hard to get a hold of, is all.
If you have a better solution please share it. Getting stoned on weekends is fine, but I got to see the whole "faces of meth" before and after thing in person over a year, and it was not pretty.
Meth is controlled and yet your employee still managed to get it. Obviously criminalizing it doesn't prevent people from having access to it. What it does prevent is quality control.
Your employee was not any less addicted due to the criminalization of drugs.