The popular weight-loss drug orlistat — sold under the brand names Xenical and Alli — has been linked to "severe toxicity of internal organs such as the liver and kidney" and interferes with anti-cancer medicines and other therapies, a new federally funded study has found.
The University of Rhode Island study, published in the journal Biochemical Pharmacology, found the negative effects of the drug are irreversible and can be caused by a low level of the medicine.
"Since it has been available over–the-counter, there has been a drastic increase of toxicity among patients using the drug," said Bingfang Yan, who led the study funded by the National Institutes of Health. "It has been linked to severe liver failure, acute pancreatic failure and acute renal [kidney] failure."
Professor Bingfang Yan's study funded by the National Institutes of Health, also found that the drug alters efficacy of medicines, and particularly limits the effectiveness of some anti-cancer drugs.
Yan has alerted the U.S. Food and Drug Administration to his findings.
Orlistat was originally approved by the FDA in 1999 as the prescription drug Exenical, and was then cleared in 2007 as the over-the-counter medication Alli. Yan said it has been the most commonly used medicine to treat obesity for more than a decade.
Yan said orlistat works in the intestinal tract by preventing fat from being absorbed by the body. But he added that the medication itself is “absorbed, and certainly internal organs such as the liver and kidney are exposed to this drug upon absorption."
His research showed orlistat hinders the action of a detoxification enzyme in the liver, kidney, and gastrointestinal tract.
"When the activity of this enzyme drops in those organs, toxicity increases or the efficacy of some drugs are altered," Yan said. "This study shows that orlistat profoundly alters the therapeutic potential of the anti-cancer drugs. In the case of the anti-cancer drugs, it weakens their effectiveness."
Yan’s study isn’t the first to raise concerns about orlistat.

In 2010, the Food and Drug Administration issued a warning on orlistat, citing the potential for liver toxicity.