The effects and side effects of medical cannabis are not well-established. In 2018, cannabis was approved as a medical drug in Denmark - giving all doctors the opportunity to subscribe medical cannabis to their patients. In this case report a 64-year-old kidney-transplanted woman started cannabis droplets due to chronic back pain, which resulted in increased appetite, weight gain and development of diabetes mellitus. Patients with an increased risk of developing diabetes may be more prone to this under the treatment with cannabis. Further studies are needed.