I know people who have been smoking a lot - also before practicing. I have never actually experience any of them harming anyone while under influence - however it IS illegal and I don't think it's up to each person to decide wether he or she can practice under the influence of drugs. Just don't do it!!! I very much second Colleen's mail.
Of course we all have flaws and strange habits (I myself CRAVE coffee in the morning
) and we should - to a certain extend - be lenient to each other while we are going through our individual development. However deliberately manipulating your senses before practicing seems to me to be too much of a risk taken on behalf of your class-mates.
As every one might have guessed by now I have no personal experience with getting high on any illegal substance. And the only thing that get me high on the mat is when the practice is going really well. Actually I would prefer that 'natural high' over any form of substance-produced high (yes - even over the buzz of a good single-malt whisky
In my opinion Aikido practice is not 'an experience' but more like time and effort dedicated to progress. Therefore we should walk the path with firm steps and awareness and not try to fly down it while hovering on a cloud - no matter what color it might have.