Ess is (of course) right on about the potential for liver damage. Interferons can cause it.
Alcohol can cause it. I bet mixing the two more than doubles the risk.
Alcohol shouldn't be mixed with Baclofen, antidepressants, pain medications, etc. You are right -- It simply isn't helpful in the long run.
I doubt your friends will be overly concerned about any risks to their health because
1) Alcohol may be serving to decrease some of their parasthesia sensations (a treatment!