The ceiling dose with Buprenorphine is subjective. 32mg is a dose at which most people still experience an increase in mu agonist effects- so it was chosen to be the dosing cutoff in BMT protocol. Some people still experience additional mu agonist effects at higher doses, some people hit the ceiling dose (meaning no more additional mu agonist effects at higher doses) at a dose lower than 32mg.
The pleasurable mu agonist effects (warmth, euphoria, etc) is generally agree'd to stop increasing above 12-16mg in most people. Sedation, relaxation, constipation, and other CNS and peripheral mu agonist effects are what increase with additional higher doses between 12-16mg and 32mg in most people.
In countries and areas where there are massive IV Buprenorphine addict populations, you don't find people injecting large doses. A single 8mg Subutex is usually crushed to a powder, divided into 8 equal piles and each pile (1mg Bupe) is sold as one dose to IV (countries like Georgia, India, Bangladesh, etc).
The benefits to more Buprenorphine recreationally ends before the ceiling dose. For maintenance purposes doses up to 32mg provide additional benefits such as craving reduction; for a recreational user, it would add no pleasurable benefit and only skyrocket tolerance to the euphoria and pleasurable aspects of IV Buprenorphine.
