The graph isn't a very good representation of cost vs addiction. All it realistically shows is that between 1% & 2% of the US population over 40 years have a drug addiction.
The cost isn't a very good representation if it doesn't take into account inflation.
Nor are the % population much use as the country has approx. 100m (50%) increase in population over 40 years too. A graph given the total addicts vs the cost PA (corrected for inflation) would imo be a much better representation, along with a representation of population.