Are you required to notify all current or future employers if you've been in drug rehab?

If you've been in a drug rehabilitation program, and successfully completed it, do you have to notify any potential employers? Do you have to notify a current employer if you're going into a rehab program?

I assume the laws are differen in every state, but specifically in Illinois or california? If anyone knows a website that would tell me all this i'd really appreciate it.

: http://alcoholdrugstreatment.info/are-you-required-to-notify-all-current-or-future-employers-if-youve-been-in-drug-rehab