Fentanyl is an opioid that can be detected in the body through a urine test for up to 24 hours, a blood test for up to 12 hours, a saliva test for up to 2 days and a hair test for up to 90 days. This medication doesn't provide relief for that long, and it has a half-life of 219 minutes, according to Drugs.
Fentanyl can be administered transdermally through a patch, parenteral through an injection or an I.V. push or transmucosally via a dissolving unit in the mouth. Because fentanyl is so powerful, taking it exactly as directed is vital to ensure patient safety.