A partial µ-opioid receptor agonist, its mixed agonist/antagonist activity affords it a lower risk of dependence and abuse than full µ agonists like morphine. Meptazinol exhibits not only a short onset of action, but also a shorter duration of action relative to other opioids such as morphine, pentazocine, or buprenorphine.[1]
you would find it faster by googling it then waiting for someone that knows what it is :)