There's being open, then there's egregious TMI violations. There's need to know, and there's getting in someone's business. It's important to know the difference.
What's magical about the word "medication" anyway? We need to tell our instructors about everything we take that's called "medication", but don't need to tell them about anything else? That doesn't make any sense. Alcohol isn't called a "medication", but it has an effect that's much more relevant to training than aspirin, which IS a "medication". You can choose to follow a rule that you've made up based on a label, or you can use common sense. Your choice.
I feel the need to be open about my need to go out for a beer occasionally after Aikido class... generally with the instructor as well as the other students. This seems like a good way to let him know about my alcohol use!
Seriously though, Mary and Janet are absolutely correct and said everything that needs to be said.