Amphetamines are a type of central nervous system stimulant.
Alcohol, on the other hand is a Central nervous system depressant. On the other hand, at least in rats, alcohol inhibits the liver from breaking down amphetamines, and therefore, can actually increase the actions of amphetamines which could cause increase anxiety, tremor, insomnia, etc. Therefore, I do not recommend alcohol in one who is on Adderall. Somewhat surprisingly, a Medline search did not reveal as much data as I thought your question would elicit, but nevertheless, it is a good question. Alcohol Clin Exp Res.