I tweaked and skated dozens of times back in the day, although Im not sure how healthy it was. But stims put me too "on edge", I could never polish a trick or anything, I lacked the patience and focus to work on any single trick for any amount of time. Weed is the single best drug to skate on, it doesnt impair patience/focus and ability like other drugs IME, it actually helps in these areas.
Id leave the stims for when you need to clean out your room/garage, and bring a couple bowls of weed when youre on the skate...