Side effects are typically mild and can include nausea, vomiting, diarrhea, and constipation. These side effects usually subside within 2–3 weeks, with nausea being considered an "on target" side effect that helps reduce your caloric intake.
Less common but more serious side effects can include allergic reactions, low blood sugar, kidney problems (especially if you are very dehydrated), gallstones and pancreatitis. Thyroid tumors or cancer has been observed in rodents, but not yet humans.