I drink one or two glasses of wine every two months, so really not a lot, almost nothing, I can go for a year without too. My hospital is ok with that, we have to fill in a questionaire every 6 months that has all kinds of question, including if you drink and how much.
I don't know if you have that in the US too, but if you do and your friends fills it in according to the truth, that he will hear what his team thinks of it...
I do know that they don't want you to drink too much. Like Kevin says, it can mess up your anti-rejection levels and the meds we're on are already bad for your liver.. So with that it's not good to add something that can mess with your liver even more.