Cannabis use in the United States has doubled in the past 10 years,1 with an estimated 22 million people using the drug in 2014.2 In addition, an increasing number of states now allow the use of medical cannabis or are considering legalizing recreational cannabis. Health care professionals are frequently asked by patients and their families about using cannabis and how it may affect health. Given these trends, it has become important to obtain longitudinal data on the health effects of long-term cannabis use.