The main side effect is pretty gross. Can u say ANAL LEAKAGE!!!

There are only side effects if you go over 15 fat grams per meal.

explosive diarreah...there's a warning on the bottle...

diet pills are lame.
stop taking the easy way out, and go exercize.

Headaches, ungodly bathroom habits with a bad smell and oil leakage, this happens if you eat to much fat though. You are to eat right and excercise while using this product. Over all you can lose apx 30-40 pnds if you follow the program. I have never used Alli but its suppose to be like zenical i think that is how you spell it. You can Google search it to get more info on it before you try it...