Trouble Ahead: 16 yr-old son drinking alone in his room

I would be pretty worried.  First of all, a 16-year-old drinking is not great.  A 16-year-old drinking to help him get to sleep is DEFINITELY not great.  It is likely symptomatic of something deeper going on.  A 16-year-old drinking alone in his room is also a bad sign.  And to top it off, he says "it's no big deal."  This does not sound like it's going in a good direction. I think you would be wise to start looking for ways to get involved now before it gets worse.  This might mean finding an adult he trusts, if it's not you; speaking to the guidance counselor at school; getting in touch with a therapist who deals with adolescents, or substance abuse issues, or both; or anything else you can think of that won't result in him just rebuffing your concerned words.

Good luck.