Intranasal fentanyl has been used safely and effectively in many studies. There are no reports of any serious side effects with the small dose (100 mcg) that is being used in this study. Intranasal fentanyl is generally well tolerated with no serious adverse events. In cancer patients treated for breakthrough pain, the main treatment related side effects were nausea, vertigo, dizziness, constipation, and somnolence. For local side effects, fentanyl displays little local irritation, nasal discomfort or taste experiences. Nasal irritation, skin pain, nasal mucosa ulcers and dysgeusia have been occasionally reported as minor side effects.