Orlistat is an oral medication to aid in weight loss. The drug inhibits the intestinal enzyme lipase. Lipase breaks down dietary fat into smaller substances that can be absorbed by the intestine into the bloodstream. By blocking lipase, orlistat prevents absorption of a portion of the fat consumed in the diet, thereby aiding weight loss. Prescribing information indicates orlistat prevents absorption of roughly 30 percent of dietary fat intake. Orlistat is available in prescription and nonprescription strengths. The most common side effects of orlistat occur due to the presence of an abundance of undigested dietary fats in the intestines.
Fatty Leakage
The U.S. Food and Drug Administration (FDA) approved prescribing information for orlistat notes more than one-quarter of people taking the drug experience involuntary leakage of a fatty discharge from the rectum. This discharge may soil clothing. The likelihood of this side effect increases when the recommended dietary restriction of no more than 30 percent of calories at any given meal coming from fat is exceeded.
Fecal Discharge with Flatulence
According to the FDA-approved prescribing information, orlistat causes flatulence (passing gas) with associated involuntary discharge of fecal material in approximately 24 percent of people taking the medication. Consumption of fats in excess of 30 percent of the total daily caloric intake increases the risk of this side effect.
Fecal Urgency and Incontinence
The manufacturer of prescription strength orlistat states that approximately 22 percent of people taking the medication report fecal urgency--an overwhelming need to immediately evacuate the bowels. Roughly eight percent of people on the medication reported incidents of involuntary loss of bowel contents related to uncontrollable fecal urgency. Exceeding the recommended dietary fat limit increases the likelihood of experiencing this side effect.
Increased Bowel Movement Frequency
Approximately 11 percent of people taking orlistat report increased frequency of bowel movements, as noted in the FDA-approved manufacturer's prescribing information. Dietary fat intake exceeding the recommended limits increases the likelihood of this side effect.
Nausea and Vomiting
According to the manufacturer's prescribing information, studies examining the side effects of orlistat found approximately eight percent of people experience nausea, and four percent experience vomiting while taking the drug.
Headache
Research conducted to determine the safety and efficacy of orlistat found approximately 31 percent of people on the medication report headaches, according to the manufacturer's prescribing and patient information materials.
Irregular Menstruation
The manufacturers of orlistat report that during research trials studying the effects of the drug, approximately 10 percent of women reported irregular menstruation.
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