Please use this link to access this publication. Abstract Background Use of cannabis to alleviate multiple sclerosis (MS)-related symptoms is increasing. Due to strict regulations, only a minority of MS patients receive cannabis-based prescription drugs. The extent of recreational and medical cannabis use among Danes with MS is unknown. Our aim was to evaluate the prevalence of illegal and legal use of cannabis in MS patients, as well as reasons for use and perceived adverse effects. Methods An anonymous questionnaire was sent to all 3606 patients at the Danish Multiple Sclerosis Center, Rigshospitalet, University of Copenhagen. The questionnaire included questions about sociodemographic factors, clinical characteristics and medical...