Xenical

Orlistat works by inhibiting pancreatic lipase, an enzyme that breaks down triglycerides in the intestine. Without this enzyme, triglycerides from the diet are prevented from being hydrolyzed into absorbable free fatty acids and are excreted undigested. Only trace amounts of orlistat are absorbed systemically, the primary effect is local lipase inhibition within the GI tract after an oral dose. The primary route of elimination is through the feces.
 
At the standard prescription dose of 120 mg three times daily before meals, orlistat prevents approximately 30% of dietary fat from being absorbed.
 
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Linked from http://en.wikipedia.org/wiki/Xenical
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The primary side effects of the Xenical are gastrointestinal-related. Side effects are most severe within the first year of therapy. Because orlistat's main effect is to prevent dietary fat from being absorbed, the fat is excreted unchanged in the feces and so the stool may become oily or loose. Increased flatulence is also common. Bowel movements may become frequent or urgent. Rare occurrence of fecal incontinence have been seen in clinical trials. To minimize these effects, foods with high fat content should be avoided.
 
The absorption of fat-soluble vitamins and other fat-soluble nutrients are inhibited by the use of orlistat. A multivitamin tablet containing these vitamins (A, D, E, K, and beta-carotene) should be taken once a day, at least 2 hours before or after taking the drug.
 
Despite claims that orlistat increases the risk of breast cancer amongst clinicial trial participants, there is evidence to suggest that the introduction of specific varied preparations containing orlistat can induce cell death in tumor cells and block their growth.
 
A recent animal study addressed a connection orlistat shares with aberrant crypt foci (ACF) in the colon, which is believed to be one of the earliest precursors of colon cancer.
 
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Linked from http://en.wikipedia.org/wiki/Xenical
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