Most recommendations are terrible in this thread. Tricombs first recommendation of LOW DOSE methamp is probably the best as far as real drugs go... IF you can keep the dose low maby you won't have any major side effects.
Yes, clean coke doesn't have a bad comedown for many of us, but is apparently hard to come by now days isn't it? Considering the vast vast majority of street coke has levamisole in it, and the even wose stuff has that levamisole+whatever other nasty shit some idiot low down dealer could put in (if you don't have a good hook that is. And even if you do, lets go back to mentioning levamisole...).
MPH imo is a terrible recommendation.
I'd say that proper diet (meaning eating MORE than you normally would while having a healthy sober day), lots of sleep, and some supplements around would be your best bet as far as minimizing negative effects if you do use meth or something along those lines. But better yet, look into the supplements I mentioned before if you're looking to avoid those side effects you mentioned.. And better yet, do that and exercise in several ways and you'll notice an improved mental state all the time.