Define drug abuse. when does drug addiction occur?

Drug addiction is a brain disease because the abuse of drugs leads to changes in the structure and function of the brain

Drug addiction occur after excess drug intake

above statement is not a true statement about the open ocean because the open ocean has low levels of nutrients. most of the photosynthetic activity on earth occurs in the open ocean within the photic zone. organisms in the deep ocean are exposed to frigid temperatures and total darkness but it does not begin at the low-tide mark.