Comparison of Pharmacological Activities of Buprenorphine and Norbuprenorphine: Norbuprenorphine Is a Potent Opioid Agonist At the δ-receptor, norBUP was a potent full agonist, yet BUP had no agonist activity and antagonized actions of norBUP and DPDPE.
At μ- and κ-receptors, both norBUP and BUP were potent partial agonists, with norBUP having moderate efficacy and BUP having low efficacy.
Buprenorphine will be euphoric for people with little opioid experience. However, if you have used full agonists for a while, you simply won't feel the effect as a traditional opioid. Bup binds extremely tightly to the mu-opioid receptor, but the stimulation of the receptor is only 30% (100% for any full agonist like morphine, oxy, heroin, demerol, fentanyl, etc) so while for opioid naive people this still will result in opioid-like effects, for people who are tolerant, it can only have about 30% of the effects of a full agonist, so they don't feel it.Can anyone explain this mystery to me? Why does it not produce a similar IV effect as Heroin, Oxy, Morphine etc? I remember a rush from Temgesic many years ago.