Illegal cannabis use is common among Danes with multiple sclerosis.

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.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 or recreational cannabis use.Questionnaires were completed by 2244/3606 (62%), of which 2009 questionnaires from patients with MS or clinical isolated syndrome (CIS) were valid for analysis. Forty-nine percent (980/2009) had used cannabis at least once. Cannabis was used within the past year (current user) by 21%, and only 21% of those received prescribed cannabis-based medicine. Recreational use was reported by 17%. The primary reasons for use were to alleviate pain (61%), spasticity (52%) and sleep disturbances (46%). The most common adverse effects were drowsiness (30%), feeling quiet/subdued (23%) and dizziness (13%). Almost half (44%) of the non-cannabis users would consider use of cannabis to alleviate MS symptoms if the drug was legalized.This study shows that illegal cannabis use is common among Danes with MS as only 21% of the current cannabis users received prescribed cannabis-based medicine. Current cannabis users reported high efficacy in relieving pain, spasticity and sleep disturbances. In addition, only mild to moderate severity of adverse effects were reported. To the best of our knowledge, this is the most comprehensive survey of cannabis use among MS patients.