BACKGROUND The public health consequences of the legalization of marijuana, whether for medical or recreational purposes, are little understood. Despite this, numerous states are considering medical or recreational legalization. In the context of abrupt changes in marijuana policy in 2009 in Colorado, the authors sought to investigate corresponding changes in marijuana-related public health indicators. METHODS This observational, ecologic study used an interrupted time-series analysis to identify changes in public health indicators potentially related to broad policy changes that occurred in 2009. This was records-based research from the state of Colorado and Denver metropolitan area. Data were collected to examine frequency and trends of marijuana-related outcomes in hospital discharges and poison center calls between time periods before and after 2009 and adjusted for population. Analyses were conducted in 2014. RESULTS Hospital discharges coded as marijuana-dependent increased 1% per month (95% CI=0.8, 1.1, p<0.001) from 2007 to 2013. A change in trend was detected in poison center calls mentioning marijuana (p<0.01). After 2009, poison center calls increased 0.8% per month (95% CI=0.2, 1.4, p<0.01). Poison center calls also increased 56% (95% CI=49%, 63%, p<0.001) in the period following the policy change. Further, there was one hospital discharge coded as dependent for every 3,159 (95% CI=2465, 3853, p<0.001) medical marijuana registrant applications. CONCLUSIONS The abrupt nature of these changes suggests public health effects related to broad policy changes associated with marijuana. This report may be used to assist in policy decisions regarding the short-term public health effects of marijuana legalization.