Drinking alcohol, in and of itself, is not a sin. The Catechism of the Catholic Church states…
2290 The virtue of temperance disposes us to avoid every kind of excess: the abuse of food, alcohol, tobacco, or medicine. Those incur grave guilt who, by drunkenness or a love of speed, endanger their own and others’ safety on the road, at sea, or in the air.
So the above defines specific grave or mortal sins associated with drunkenness but I can think of others. Some abuses of alcohol that lead to other mortal sins may also be mortal - drinking to the point of losing control of one’s temper and hurting someone comes to mind. Drinking on the job and endangering your livelihood, especially if you are supporting a family might be another.