what is fentanyl drug effects what is fentanyl drug effects? When used consistently, fentanyl and other opioids can cause the following long-term effects: Dependence Addiction Brain changes Organ damage Respiratory issues. The most common side effects of smoking fentanyl include: Nodding off; Dry mouth; Clouded thoughts; Extreme itching; Heaviness in your arms and legs; Nausea […]