Most slimming pills are high in caffeine thus making you lose appetite & lose water weigh. That's why its not recommended to take at night. Consuming lots of caffeine will also make u jittery, skin tingle, and sometimes diarrhea, headache, anxious, etc.

There's no magic pill that burn fat directly as far as i know. Only dangerous drugs can do that. Don't listen to anyone that offer you product that can burn fat. It's always the indirect way.