Side effects are reported in some persons, but not all of patients taking generic Relafen drug will experience them. Adverse reactions to be aware of before you buy Relafen include heartburn, diarrhea, headaches, dry mouth, sun burn, blurred vision, and muscle weakness. Some patients have reported appetite loss, fever, and changes in their stools. Generic Relafen drug is in the NSAID class of drugs. This class of medication is known to cause fluid retention in some patients that can lead to edema.