C22H28N2O -
N-Phenyl-N-(1-2-phenylethyl-4-piperidyl) propanamide
Fentanyl is a powerful synthetic narcotic (an opioid, actually) that is one of the most widely used painkillers for surgery. Like most narcotics, it can produce euphoria, and is a popular drug used illegally, especially by medical personnel, as they have less restricted access to it.
It is most often administered intravenously, but is also available in patch form under the name Duragesic.