Cannabidiol for Fibromyalgia -The CANNFIB Trial Protocol for a Randomized, Double-blind, Placebo-controlled, Parallel-group, Single-center Trial

BACKGROUND: Fibromyalgia is a serious chronic pain condition affecting 2-5 % of the background population. The disease burden in most affected individuals is substantial; with widespread musculoskeletal pain, high pain intensity, often accompanied by sleep disturbances, fatigue, cognitive dysfunction, and emotional distress. Fibromyalgia is associated with disability and muscle fatigue, affecting daily life activities, leading to poor social participation and incapacity for normal employment. Studies have shown that many patients, are not satisfied with the treatments offered, and rate their health and quality of life after treatment as poor.

There is currently is no cure for fibromyalgia, and management aiming at symptom reduction and maintenance of optimal functioning is recommended by clinical guidelines, including both non-pharmacological and pharmacological treatment strategies. Recommendations for the pharmacological treatment of fibromyalgia propose antidepressants and anticonvulsants, which target central pain processing mechanisms. These treatments have been tested in controlled trials for their efficacy in patients with fibromyalgia, and meta-analyses on these interventions have revealed that overall effect sizes are modest, as only a minority of patients have substantial benefit (patient reported pain relief of 50% or greater), while more have moderate benefit (patient reported pain relief of 30% or greater). Many patients have no or minimal benefit or will discontinue the treatment due to side effects. However, it appears that even moderate reductions in pain may lead to considerable increase in self-reported quality of life and other outcome domains in this specific patient population.

Medical cannabis is popularly advocated for different health conditions including chronic pain, both among politicians and in the general population in Denmark, although evidence is sparse efficacy and on what types of medical cannabis to use and what dosages to prescribe for the different conditions. In addition, safety issues such as adverse events and serious adverse events is not properly assesed. Physicians are reluctant to prescribe medical cannabis to their patients, and many patients living with chronic pain are known to self-administer unlicensed medical cannabis. The extent of actual cannabis use is unknown, although, one study has documented that 13% of patients with fibromyalgia use cannabis regularly with a more extensive use among male patients compared to females. Numbers from a Danish context show that only 17 out of 286 (6%), patients with fibromyalgia participating in a multidisciplinary rehabilitation program in Bispebjerg and Frederiksberg hospital during 2018, stated that they were using self-administrated cannabis on a regular basis (unpublished data). As self-administrated off-label use of cannabis is illegal in Denmark, this number may well be underreported. Still, individuals diagnosed with fibromyalgia who do admit to cannabis use, are sharing stories with health professionals about how unlicensed cannabis has improved their coping with everyday life, functional ability, pain, sleep, fatigue, mood and overall health related quality of life. Such compelling stories cannot be ignored and underline the necessity of exploring the efficacy of medical cannabis in a proper research design (i.e. with good internal validity).

The use of the cannabis plant for medical purposes is limited in Europe and the European addiction societies stresses the need for further studies on the efficacy and possible dangers regarding medical cannabis intake. Regulations are lacking on registration and medical indications, and the development of uniform compounds regarding strength and types of products and rules concerning sales and marketing.

In Denmark, production and distribution of medical cannabis is illegal. However, starting from January 1st, 2018, a four-year pilot scheme has been legalized and approved by the Danish Medicines Agency, allowing for medical cannabis in the treatment of conditions such as multiple sclerosis, spinal injuries and nausea after chemotherapy and neuropathic pain. Although patients suffering from fibromyalgia have few treatment options for management of their disabling condition, this group is not included in the pilot scheme. However, it is legal for physicians to prescribe cannabis for this and other patient groups.