Microeconomic theory explains that these goods are considered complementary goods. Complementary goods are those whose consumption increases / decreases together. If consumption of good A increases, consumption of good B increases. If consumption of good A decreases, consumption of good B decreases. This is exactly the context described by the research, the rigorous measures taken by universities led to the reduction in alcohol consumption. And the reduction in alcohol consumption has reduced marijuana consumption. This is because these are goods considered complementary by economic theory.