1) Synthetic opioids like fentanyl are much more potent than natural opioids like morphine and heroin. They work by binding to opioid receptors in the brain and spinal cord, triggering feelings of euphoria but also slowing respiration.
2) Synthetic opioids carry a high risk of overdose due to their potency and unpredictability. Overdose occurs when respiration slows to the point of stopping, depriving the brain of oxygen.
3) Signs of opioid addiction include an inability to control use, cravings, and changes in sleep, appetite, hygiene and social activities. Addiction results from the drugs' effects on the brain's reward pathways.