DrugDigest: Fentanyl ( Duragesic ): Information on dosage, usage, side effects, interactions, and drug comparisons, including generics when available.Duragesic: Product information for US health care providers and consumers.Duragesic: Full prescribing information from RxList.MedlinePlus: Fentanyl Skin Patches: Features information about dosage, usage, warnings, and side effects.