They can generally tell about how much they’ll need, and only consecrate that amount. There’s always some left over, but the Eucharistic ministers (lay people who help distribute the Eucharist) usually drink that, and even if the priest drank all of it, it’d be less than a standard-sized glass of wine in total from each mass. A couple of drinks a weekend isn’t going to turn anyone into an alcoholic.
Now, it’s possible that a priest might deliberately consecrate significantly more than is needed, or hit up the bottles of unconsecrated wine before or after masses, and drink to excess, but in that case, it’s hard to blame the behavior on the sacrament.
I wasn’t blaming it on the sacrement, just asking because of something I read years ago.
Also, I believe Eucharistic ministers (my father’s one, btw) have only been around since Vatican II. Before then, only priests could touch the Eucharist.
From what I understand, there were Eucharistic ministers before Vatican II, but they were regarded as a last resort sort of thing: If you absolutely didn’t have enough priests, then it was allowable, though discouraged. After Vatican II, though, the Church not only allowed Eucharistic ministers, but actively encouraged them: Even if you have a dozen visiting priests, it’s still better for lay folks to do the job.
Take this with a grain of salt, though, since that was well before I was born.