Many people with ADHD self-medicate with alcohol or drugs (as well as many with anxiety). The key to quitting alcohol is to find medication that has a similar effect for you. Working with a clinician that is well-versed in adult ADHD and addiction is ideal.
This Expert Answer echos the comment above:
It’s tough to quit using something that is working for you, even when you know it isn’t an appropriate solution.
ADDitude Community Moderator, Parenting ADHD Trainer & Author, Mom to teen w/ ADHD, LDs, and autism