True, however I'd love to see a licensing agency revoke or refuse a license because someone drank alcohol while off duty (to clarify, use does not equal abuse before the concept of alcoholism is brought up), used tobacco, or held a CCW permit.
But if you test positive for drugs and alcohol at work, you may be terminated. If you carry a weapon at work, you may be terminated. If you test positive in a "no smoking" job such as a hospital or FD, you may be terminated.
If you test positive for drugs and alcohol in a pre-employment physical, you will not be hired.
If a drug stays in your system long enough to be detected, tough for you.
If you do not have enough sense to obey the laws, you should not be working with patients. If the drugs you consume are illegal, change the laws. You could be one of those fine examples petitioning for MM in Sacramento.