My singing voice has actually improved since the beginning of summer, and I've been smokin' almost every night. Hahahah. I love getting high and singing/dancing. rockin' out and singing, disco dancin'.. wait. Shhhhhhhhhhhaddafuckup. please?
Your theater department should have a voice instructor who can give you the benefit of their experience.
1. Take TINY hits & don't smoke more than a dime. 2. Drink one-half to 1L of water You should be fine. Just be reflective and be yourself when you perform. So you sacrifice a year of your life for a better performance. People do it. (Bernstein, etc)
Dunno 'bout weed, but alcohol greatly improves my bagpiping performance. The more my audience has had to drink, the better I sound.
Edit: I am referring to smoking the night before a performance. I don't think performing high does you or your audience any favors, especially if you are starting out. You negate the performance high by replacing it with the artificial weed-high. So, if your performance is sucking, you wouldn't know because of the weed. That's why you need your natural adrenaline completely in-check.
Once I started doing stand up, I had to cut back on my smoking. If it affected my voice telling jokes, I can only imagine how awful I'd sound if I tried to sing. Then again, at my best I sound pretty awful when I sing...