Fentanyl is an opioid, a potent narcotic analgesic, which can be used for sedation and analgesia during anesthesia, but has adverse effects such as respiratory depression. Fentanyl is an opioid agonist with sedative and analgesic effects, and the injection can be used for sedation and analgesia before, during and after surgical anesthesia. Fentanyl is contraindicated in bronchial asthma, in persons with a history of hypersensitivity to this drug, and in patients with myasthenia gravis, and should not be combined with monoamine oxidase inhibitors such as phenelzine. Fentanyl may cause adverse reactions such as dizziness, blurred vision, nausea and vomiting, hypotension, and even serious discomfort such as respiratory depression, asphyxia, and muscle rigidity. Feedback to your doctor immediately in case of discomfort. Fentanyl is a narcotic drug controlled by the state and can be addictive, it should be used in strict compliance with the regulations and under the guidance of a doctor.