Riding the global waves of decriminalization, medical or recreational use of cannabis (Cannabis sativa spp.) is now legal in more than 50 countries and U.S. states. As governments regulate this formerly illegal crop, there is an urgent need to understand how cannabis may impact the environment. Due to the challenges of researching quasi-legal commodities, peer-reviewed studies documenting environmental impacts of cannabis are limited, slowing the development of policies and agricultural extension guidelines needed to minimize adverse environmental outcomes. Here we review peer-reviewed research on relationships between cannabis and environmental outcomes, and identify six documented impact pathways from cannabis cultivation (land-cover change, water use, pesticide use, energy use, and air pollution) and consumption (water pollution). On the basis of reviewed findings, we suggest policy directions for these pathways. We further highlight the need to formalize existing traditional and gray literature knowledge, expand research partnerships with cannabis cultivators, and ease research restrictions on cannabis. Finally, we discuss how science might contribute to minimize environmental risks and inform the development of regulations for a growing global cannabis industry.