States that have legalized weed see drop in use among those under 18 study says Science is fucking lit, Science

The study found the drop in underage weed usage only in states that had legalized recreational weed. The study spans 14 years (from 1993 through 2017), and recorded responses from 1.4 million students. Researchers saw an 8% decline in underage marijuana usage in those states. The paper hypothesized that the cause for the drop may be that "it is more difficult for teenagers to obtain marijuana as drug dealers are replaced by licensed dispensaries that require proof of age."