In 2009, the Obama administration issued a memorandum (the Ogden Memo) which instructed prosecutors and law enforcement officials not to focus federal resources on individuals “whose actions are in clear and unambiguous compliance with existing state laws providing for the medical use of marijuana” (54), essentially decriminalizing medical marijuana use at the federal level. This policy shift was associated with a drastic increase in medical marijuana registration applications in Colorado (55); to our knowledge, this association has not been thoroughly evaluated in other states. As noted above, most studies in adolescents have found no measurable effect of state-level policy changes on marijuana prevalence (53); however, it is still too early to know the possible long-term consequences of legalization for individuals and society. Furthermore, almost all studies evaluating the policy effects of legalization have focused on the point in time when individual states legalized marijuana; few have focused on the policy effects of the Ogden Memo (56). Three studies that have compared pre- and post-2009 trends (in an effort to capture potential effects of the federal shift in policy) have all
