Fentanyl is a synthetic opioid significantly more potent than morphine, commonly prescribed to manage severe pain, especially after surgery or for chronic pain patients. Due to its high strength, fentanyl carries a high risk of addiction. Withdrawal Symptoms Withdrawal symptoms typically begin 8 to 24 hours after the last dose and can last up to 10 days. Common symptoms include nausea, vomiting, muscle cramps, insomnia, and intense cravings. Signs of Overdose Be alert to signs of fentanyl overdose, which include difficulty breathing, clammy skin, and confusion or disorientation. Overdose requires immediate medical attention.