Other known side effects associated with fentanyl products include: • Very common side effects (affects more than 1 user in 10 people): excessive sweating • Common side effects (affects 1 to 10 users in 100): feeling confused, feeling anxious or nervous, hallucinations, abnormal thinking, muscle twitching, difficulty sleeping, strange dreams, tongue or taste problems, flushing, mouth ulcers/ blisters, blockage of the gut, difficulty swallowing, being accident-prone • Uncommon side effects (affects 1 to 10 users in 1,000): feeling restless, feeling detached, moodswings, trembling, difficulty speaking, being forgetful, loss of coordination, vertigo, slow or fast heartbeat, high blood pressure, difficulty breathing, slow or shallow breathing, asthma, bloating, wind, thirst, difficulty going to the toilet, change in frequency of going to the toilet, feeling unwell • Rare side effects (affects 1 to 10 users in 10,000): hiccups • Very rare side effects (affects less than 1 user in 10,000): irregular heartbeat, stopping breathing, blood in the saliva, decrease in amount of urine, painful contraction of the bladder