Get emergency medical help if you have signs of an allergic reaction to orlistat: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Stop using orlistat and call your doctor at once if you have:
severe stomach pain;
severe pain in your lower back;
blood in your urine, painful or difficult urination;
signs of kidney problems including little or no urinating; swelling in your feet or ankles; feeling tired or short of breath; or
signs of liver problems including nausea, upper stomach pain, itching, tired feeling, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes).
Common orlistat side effects are caused by its fat-blocking action. These are signs that the medicine is working properly. These side effects are usually temporary and may lessen as you continue using this medicine:
oily or fatty stools;
oily spotting in your undergarments;
orange or brown colored oil in your stool;
gas and oily discharge;
loose stools, or an urgent need to go to the bathroom, inability to control bowel movements;
an increased number of bowel movements; or
stomach pain, nausea, rectal pain.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
 Orlistat side effects (more detail)
