As with other antibiotics, generic Ilosone medication may cause some side effects. These side effects include stomach upset, diarrhea, loss of appetite, nausea, vomiting, and stomach cramps, typically last just a few days. If these symptoms persist or become severe, contact your local doctor. Quickly contact your local doctor if any of the following infrequent side effects do occur: dark urine, pale stools, severe stomach pain, unusual lethargy or weakness, yellowing of the eyes or skin. In the unlikely event that you have an allergic reaction after you buy Ilosone, see your local doctor immediately.