Normal ...
You used the phrase,'normal' to describe your friends ability to drink alcohol. Normal usually means that they digest alcohol, at roughly the rate of about 1 and a quarter oz. per hour....
It may be, that you are like me, in Chapter 3 of the book,'Alcoholics Anonymous' described as a 'real alcoholic', which simply means that my body digests alcohol at a much slower rate. Result the alcohol (drug) stays in my body, sending messages to my brain saying,'I want more!'
Each time I take a drink,so the only way for that to stop, is total abstinence, if I don't take the first drink, the whole sordid, life destroying process can't start...
For me the way to combat this was to develop a knowledge and understanding of the book,'Alcoholics Anonymous' and the suggested 12 Steps, which I actively pursue to this day...plus what ever help and support is available here and at AA meetings, although they're not to everyone's taste...
I hope this helps.