Buprenorphine is?

Ans. is 'c' i.e. Partial agonist Human brain produces certain endogenous opioids.These opioids act on opioid receptors situated in the brain.There are three types of opioid receptors situated in the brain and opioids mediates their various actions through them.Different opioids have different affinities for various opioid receptors.They may be agonist to one class of receptor and antagonist to another.* A single opioid may also have dual agonist/antagonist effect on a single receptor.The opioids are classified according to their affinity on various opioid receptorsPure morphine like opioids in general acts on m and k receptors.Mixed agonists-antagonistsOpioid drugs may be agonist to one class of opioid receptor and antagonist to anotherNalorphineButorphanol - PentazocinePartial agonistsA single opioid may also have dual agonist/antagonist effect on a single receptor; these are known as partial agonists.- BuprenorphinePure competitive opioid antagonistsThey block all opioid receptors while exerting no activating effect NaloxoneNaltrexoneNalmefene More on BuprenorphineIt is a high efficacy partial agonist of the m receptor and an antagonist of the k receptor.It has less liability to induce dependence and respiratory depression than pure agonists.It is a useful analgesic because of the length and strength of its action, its low liability to cause dependence and the fact that administration by injection can be avoided.