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Robin Williams, 59, first battled alcohol and cocaine addiction in 1983 but quit cold turkey after his friend John Belushi died of a drug overdose a few hours after they had snorted cocaine together at a hotel. Williams was sober for 20 years but relapsed and sought treatment in 2006 after a 3-year drinking binge. He told People magazine in December 2009, "I found myself drinking to blackouts. It's like your brain going into witness protection."
(Photo courtesy of Steve Rhodes)