Fat, an essential part of the human diet, is calorie- and energy-rich. Over-consumption of fat, however, can cause weight gain and associated health problems. This makes fat-blocking drugs a desirable target for pharmaceutical manufacturers that create medications to help treat obesity. Fat-blocking medicines include drugs that block the digestive enzymes that process fat as well as drugs that prevent fatty compounds from being absorbed by the intestines.
Orlistat is a fat-blocking medication available in prescription form as Xenical, though it can also be purchased over-the-counter under the brand name Alli. As Medline Plus, a website of the National Institutes of Health, explains, orlistat works as a lipase inhibitor. Lipase is an enzyme made by the pancreas which helps the digestive system break down fat. Dietary fat cannot be absorbed by the intestines until it is acted upon by lipase. By inhibiting the action of lipase, orlistat is able to prevent the intestines from absorbing some of the fat from a meal. This medication can be prescribed for people who are overweight and unable to lose weight using diet and exercise alone. Because orlistat prevents fat from being completely digested, it can cause some gastrointestinal side effects. The most common side effect is oily spotting, which can sometimes appear in the user's underwear. This is the result of undigested fat passing rapidly through the intestines and may be accompanied by gas, bloating and pain in the abdomen. Some patients also experience diarrhea combined with fatty and foul-smelling stool.
Another important component of fat is cholesterol, another type of lipid. Ezetimibe is a prescription medication that blocks the ability of intestinal cells to absorb cholesterol. Ezetimibe is especially useful for patients who have a condition called hyperlipidemia, which is caused by the blood having too many lipids, the breakdown products of fat. Much like orlistat, ezetimibe can cause diarrhea and other gastrointestinal problems, but it can also cause headache, sore throat, joint pain and dizziness. In rare cases, ezetimibe can cause liver damage, which can lead to jaundice and abdominal pain.
Cetilistat, not yet approved for use in the U.S., is a lipase inhibitor that Drug Development-Technology says is currently in phase III clinical trials in Japan. This means that its safety and effectiveness are promising enough for this drug to receive additional clinical testing. Because it is a lipase inhibitor, it works similarly to orlistat but is expected to be better tolerated. It is also designed to help users control appetite. It is not known if or when this drug will receive approval from the U.S. Food and Drug Administration.