This invention pertains to a prescription drug lock box consisting of a container and a detachable combination locking cover assembly used to secure the contents held within. The container has an integrally formed key post positioned above its open end. The tumblers of the cover assembly engage the key post and lock to it thus securing contents held within. When the indicia of the tumblers and correct unlocking code are in alignment with a marker, the cover assembly may be installed or removed.