<unk> (injection) is a opioid analgesic that is FDA approved for the treatment of moderate to severe pain.   Common adverse reactions include pruritis, nausea, vomiting, constipation, xerostomia, headache, and dizziness.
Buprenorphine 
Methadone 
Naltrexone 
Tapentadol
Morphine 
Acetylmethadol
Tramadol
Levomethadone