When I told my therapist about my history of drug abuse, she didn't even bat an eye. Millions of people across the U.S. abuse drugs and alcohol every year, and many of those same people are in therapy. Therapists and psychiatrists are used to it, and it certainly won't scare them off or make them think less of you. I will say, however, telling my psychiatrist turned out to be a bad idea because when I felt it was time to increase my meds, she accused me of abusing them and refused to up my dose... so I'd be more cautious around psychiatrists personally.