"I was drinking about a fifth of Jack (Daniels) a day, doing a lot of coke. I was just very introverted, I had an issue with being insecure and always trying to get external validation... It was just never enough and I was a late bloomer. I didn't actually start drinking until I was 22." Backstreet Boys star A.J. Mclean on his past battles with sobriety and substance abuse.