In clinical trials, side effects to orlistat mainly arose from the gastrointestinal tract and were due to the pharmacological action of the drug, which prevents the absorption of food fats. Often there were such phenomena as oily discharges from the rectum, the release of gases with a certain amount of discharge, imperative urges for defecation, steatorrhoea, increased bowel movements and stool incontinence.
As a rule, these side effects are mild and transient. They appeared at early stages of treatment (in the first three months), and in most patients, there was not more than one episode of such reactions.
Patients should be informed of the possibility of adverse reactions from the gastrointestinal tract and teach how to eliminate them by better adherence to the diet, especially about the amount of fat contained in it. The use of low-fat diet reduces the likelihood of side effects from the gastrointestinal tract.
Also, the following adverse events can occur from the gastrointestinal tract: pain or discomfort in the abdomen, flatulence, loose stools, soft stools, pain or discomfort in the rectum, tooth damage, gum lesion.
There are rare cases of hypersensitivity, consisting of itching, rash, hives, angioedema, and anaphylaxis.
Infections of the upper or lower respiratory tract, influenza, headaches, dysmenorrhea, anxiety, weakness, urinary tract infections were rare on the background of orlistat treatment, but they were regarded as unrelated to the use of the drug.