In the crystal structure of a semi-synthetic opioid drug buprenorphine, C29H41NO4 {systematic name: (2S)-2-[(5R,6R,7R,14S)-9α-cyclo­propyl­methyl-3-hy­droxy-6-meth­oxy-4,5-ep­oxy-6,14-ethano­morphinan-7-yl]-3,3-di­methyl­butan-2-ol}, the cyclo­propyl­methyl group is disordered over two sites with an occupancy factor of 0.611 (3) for the major component. One of the hy­droxy groups is involved in intra­molecular O—H⋯O hydrogen bond. The other hy­droxy group acts as a proton donor in an inter­molecular O—H⋯O inter­action that connects mol­ecules into a zigzag chain along the b axis.