Certain pharmaceutical or herbal weight-loss remedies can cause a diuretic effect, which can lead to

FDA has developed these questions and answers (Q & A’s) to help all of consumers, health care practitioners, and the general public understand FDA’s actions regarding weight loss products contaminated with various prescription drugs and chemicals.  Many of these products are marketed as dietary supplements.

Because without physical activity, the body has extra "energy" if you will, and so when it is time for bed you are not tired, so you end up staying up all night. also there is probably an effect on your internal clock, which messes with your melatonin production which goes hand in hand with your sleep cycle