Hello,, as the manufacturers say you have to have it right before or after (within an hour) of the meal. It prevents absorption of fat, n this fat goes out in the form of stool. So if you have a high fat intake of food, you will have some side effects such as passing gas, urge to go to the bathroom due to heavy bowel movements etc- this is not a negative side effect, it just causes this discomfort , and helps you flush out fat and reduce fat in your body. Expecting Side Effects : Gastrointestinal - Oily spotting, loose stools, nausea,vomiting, stomach pain and loss of appetite, few other side effects too. Diet and exercising is always a better choice over medicine.