This is all so interesting. There are so many questions people have asked each other and myself personally. I'll try to provide some answers. My history runs sort of like this. I'm 30 now. I used Heroin from about age 16ish to 25. That was all mosty heavy, injection usage... I drank pretty heavily from the start of my experimentation with drugs due to the youth culture of drinking; availability and so on. I was familiar with the concept of hangovers and all of that. My Dad drank competitively in my youth, so I got a lot of that.
I experienced hangovers following nights of drinking, but all I can say is that these hangovers were 15% of what I would experience now consuming the same amounts. I drank for years whenever I could and into college. I was addicted to Alcohol as I was many other substances. It was virtually always a "good time" when I was drunk and sometimes a little unpleasant in the morning, but nothing at all serious.
I was like this all through college. Once I went on my first teaching job and found basically any and all drugs freely available to me, I really never drank Alcohol outside of legitimate social situations where I might sip a drink with some folks. A few years later I'm 25 or so and I'm transitioning from Heroin to Methadone to nothing over the course of months. I already knew Alcohol was starting to effect me differently, but years of conditioned response led me to negate this fact. Even if Alcohol wasn't "fun" on one occasion it must have been a fluke.
The past 5 years have been essentially sobriety. 9 months, 6 months, 3 months at a time, sometimes longer. Alcohol does nothing for me. I am completely averse to it. The smell, the taste, the sensation of it as it enters my nostrils and hits my palet makes me want to gag even as I sit here writing this.
William Burroughs wrote about Alcohol and its relation to Opioid dependence in Junkie and he was the first other person I knew who experienced what I have experienced, but he mostly speaks of Alcohol being incompatible with Opioid dependence, whereas Alcohol becomes okay for him again after he completely clears withdrawal. This just isn't my experience though.
I really don't think it's a neurological thing either, which I find to be even more interesting. I've taken Benzodiazepines and Barbiturates both and couldn't discern any kind of difference in how they effected me from start to finish. I feel that the way in which Ethanol effects the mind and body is so similar to that of these other sedative/hypnotic drugs that one would expect some kind of overlap. I'm not really sure what it all means, but there appears to be some kind of definite relation in how people experience/metabolize Alcohol following or during dependece upon Opioids.