"Ahu" are stone platforms on which many moai sit. There are 313 known ahu and 125 of these carry moai. The biggest, Ahu Tongariki is 220 m (720 ft), and had the most (15) and tallest moai.
Drug misuse is not a disease, it is a decision, like the decision to step out in front of a moving car. You would call that not a disease but an error of judgment.