Does Alli have side effects?

The active ingredient in Alli, orlistat, causes digestive side effects related to undigested fats passing through your digestive system. They generally lessen over time and with proper use of the drug. These side effects include:

• Stomach pain or upset stomach
• Oily discharge from the anus
• Gas with oily anal discharge
• Oily stools
• More-frequent bowel movements
• Urgent or hard-to-control bowel movements

Other possible side effects include:

• Headache
• Back pain
• Common cold symptoms
• Menstrual changes