The most common side effects of orlistat are:
- oily spotting on underwear,
- urgent bowel movements,
- fatty or oily stools,
- increased number of bowel movements,
- abdominal pain or discomfort, and
- inability to control stool (incontinence).
From 1 in 250 and 1 in 70 patients experienced one or more of these symptoms in the first year. Generally, the side effects occurred within three months of starting therapy. In about 50% of patients, the side effects resolved within one to four weeks, but the effects in some patients lasted six months or longer. To reduce the occurrence of these side effects, meals should contain no more than 30% fat because it is the unabsorbed fat that causes most of the symptoms. alli causes fewer side effects because it contains half the dose of prescription-strength orlistat. Patients receiving orlistat with a history of oxalate kidney stones may develop increased levels of oxalate in their urine, which may increase the risk of kidney stones. Liver failure has been reported in patients treated with orlistat. Orlistat should be discontinued if symptoms of liver failure (loss of appetite, anorexia, itching, jaundice, dark urine, light colored stools, or right upper abdominal pain) occur while taking orlistat.