Buprenorphine is a derivative of the opium alkaloid thebaine and is a synthetic opioid categorized as a partial agonist at the mu-opioid receptor and an antagonist at the kappa receptor. It has a very high affinity, a slow dissociation, and a low intrinsic activity at the mu receptor and will displace other full opioid agonists such as morphine and methadone when they are occupying receptors. As a partial agonist, buprenorphine does not activate mu receptors fully (i.e., low intrinsic activity), which results in a ceiling or plateau effect that prevents larger doses from producing greater agonist effects. As a result, there is a greater margin of safety, and the risk of death from respiratory depression with increased doses of buprenorphine is significantly reduced as compared with increased doses of full opioid agonists.
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