Generic Alli pills, as with all orlistat medication, can have side effects. Uncomfortable side effects will commonly occur and signal that this med is performing as required. These include: oily or fatty stools or stains in your underwear; gas with oily discharge; loose stools or fecal incontinence; increased bowel movements; stomach or rectal pain, diarrhea, nausea or vomiting; weakness, loss of appetite, jaundice, itching, or dark urine or clay-colored stools. If you are concerned about any of these side effects, consult your local doctor. Other side effects range from cold, fever and fly symptoms to rashes, headaches and pain and more. Talk to your local doctor if concerned. Seek immediate medical attention if any signs of an allergic reaction occur, including hives, facial and throat swelling or difficulty breathing.