I took minocycline from about 1969 to around 1990 for treatment of acne. Around 1982 I noticed my teeth were turning gray. My dentist wasn't able to diagnose the problem. Minocycline was the only oral medication I was taking at the time, and I suspected it was causing the problem, but could not find any scientific documentation to prove it. I have since discovered minocycline does cause discoloration of the teeth in adults. I have had two types on in-office teeth bleaching with unsatisfactory results. I would not recommend it for long-term use.