Buprenorphine is a semi-synthetic opioid that is FDA-approved for acute pain, chronic pain, and opioid dependence and exerts its effects by acting as a partial opioid receptor antagonist. The drug is also in veterinary medicine for the treatment of pain in dogs and cats and recreationally by injection or in the nose for the high it produces. It has been reported to be the third most prevalent misused opioid, next to heroin and methadone. Buprenorphine is rapidly metabolized in the liver into major metabolites norbuprenorphine, buprenorphine-3-β-glucuronide, and norbuprenorphine-3-β-glucuronide. Very little free drug is detectable in the urine and ELISA-based drug screening assays for buprenorphine should be confirmed by mass spectrometry.