There may be some small side effects associated with the pre-workout drinks. The drinks contain large doses of caffeine and other stimulants. These in the end may end up causing other complications like diarrhea, nervousness, irritability or even weight loss. You can check out http://www.livestrong.com/article/24679-bad-side-effects-muscle-building/ for more details.
It really depends on what type of pre workout drinks you're using, and what you've digested beforehand. If it's really a problem, I would talk to your doctor or see some kind of nutritionist. Sorry I can't help more than that, but I hope this helps a little bit!