Alli is the brand name for an over-the-counter weight-loss drug known as orlistat, according to MedlinePlus. Orlistat, which also comes in a prescription-strength product called Xenical, works by preventing your body from absorbing some of the fat in the food you eat. Most people using orlistat lose 5 to 10 lbs. over six months, according to the FDA-approved drug label. The most common side effect associated with this drug is a change in bowel habits, but there are other risks as well.
Bowel Problems
You may experience a change in bowel habits, particularly in the first few weeks after beginning treatment with orlistat, according to MedlinePlus. You may have oily spotting on underwear, gas, urgent defecation, loose or fatty stools, more frequent bowel movements, loss of control of bowel movements, or pain in the rectum. If these symptoms don't go away after the first few weeks, or if they are severe, call your doctor.
Other Side Effects
You may also experience stomach pain, a change in menstrual periods, headache or anxiety while taking orlistat, according to MedlinePlus. Other symptoms are more serious. Call your doctor right away if you experience hives, rash, itching, problems breathing or swallowing, severe stomach pain that doesn't go away or is concentrated in the upper right of the stomach, fatigue or weakness, nausea, vomiting, appetite loss, yellowing of the skin or eyes, dark urine, or light stools.
Nutrient Absorption
Along with fat, orlistat blocks the absorption of some fat-soluble vitamins as well as beta-carotene, according to MedlinePlus. You may not be able to absorb enough vitamins A, D, E and K and beta-carotene to stay healthy. To prevent this problem, take a multivitamin that contains all these nutrients, according to MedlinePlus. Take the vitamin at bedtime or two hours before or after meals so that the vitamins are not blocked by the orlistat.
Liver Damage
There have been 13 reports of people who sustained serious liver damage after taking orlistat, out of about 40 million worldwide that have taken the drug, according to the U.S. Food and Drug Administration. The FDA conducted a safety review but could not find sufficient evidence to say whether or not the liver injuries reported were actually caused by orlistat. They could have been caused by a number of other factors. Only one of the 13 cases involved the use of Alli. The rest were linked to the stronger prescription product Xenical. But the FDA has added a warning about the possibility of liver damage to the label for both products.
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