Alcohol, acetaldehyde and acetic acid

Sojourn

Recent investigations have suggested that acetaldehyde may be responsible for the development of alcohol addiction. Acetaldehyde in the brain may inhibit enzymes designed to convert certain nerve transmitters from aldehydes to acids. The nerve transmitters that accumulate may then react with the acetaldehyde to form compounds which are startlingly similar to certain morphine-type compounds.

http://www.elmhurst.edu/~chm/vchembook/642alcoholmet.html