The phrase アルコールはダメなんだ is from a manga I read, in which a guy responds to his friend when being asked if he wants a beer. He appears not to be into alcohol, even goes so far to say that "I don't like the taste, nor is there any occasion for me to drink".
I'm not sure what possible meanings that phrase could have though. Literally, it'd be "Alcohol is not good", and it could be reasonably thought of as "Alcohol isn't good for your health" (in which case he might be advising his friend not to drink).
I'm curious whether there's a possibility for it to mean "I'm not good with alcohol" > "I can't drink". After all, this seems to be an example of the various ambiguous uses of "wa", in which the topic isn't necessarily grammatically tied to the modifying phrase that follows.