IMO, anything that affects your thinking can be hazardous to your poker playing, especially live. A stimulant can, effectively, put you on tilt. A depressant can dull you (and could make you sleepy.) For me, it's all about staying alert, continuing to think and make responsible decisions. (I am assuming here you know enough poker theory and have decent enough poker instincts to make such decisions.)
The most I will take is coffee, which usually does not make me particularly jumpy. Alternate coffee with water. Music can help filter out inconsequential stuff also. If I am playing a ring game, I take breaks and stop when I become tired or grumpy. A short, swift walk around the casino can help more than any drug. Do remember that any young pros who may say this is a good idea may be bluffing
you out -- because I am fairly certain they keep a stable and patient edge at a table in order to not go busto.