A Systematic Review of Fibromyalgia and Recent Advancements in Treatment: Is Medicinal Cannabis a New Hope?

Fibromyalgia syndrome (FMS) is a pain disorder characterized by chronic widespread pain, fatigue, and sleep disturbance, in the absence of any well-defined underlying organic disease. The exact pathophysiology and the mechanism which links different factors related to the disease is still unknown. Due to unknown precise pathogenesis, the coexistence of other diseases, and overlapping clinical features, FMS diagnosis may be laborious. Various treatment strategies are used, only a few Food and Drug Administration (FDA) approved, still we are facing challenges regarding effective treatment. Recently, medicinal cannabis has proven to be effective in chronic pain conditions such as osteoarthritis, neuropathic pain, and other non-cancer chronic pain. However, further research is needed about how the cannabinoid system works with the pain pathway. Using the fact that medicinal cannabis is effective in the treatment of chronic pain and certain rheumatic diseases, in this review, we aim to analyze the role of the cannabinoid system in fibromyalgia syndrome. We followed Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) guidelines in searching PubMed, MEDLINE (through PubMed), PubMed Central, and Google Scholar using keywords "fibromyalgia, chronic pain, cannabis, cannabinoids, pharmacotherapy, alternative therapy" and Medical Subject Heading (MeSH) words. After applying inclusion/exclusion criteria and checking for the quality assessment, 22 articles were retrieved and used for the analysis of the role of cannabis in the treatment of fibromyalgia. The two main compounds of cannabis with analgesic and anti-inflammatory properties are cannabidiol (CBD) and delta-9-tetrahydrocannabinol (THC), and their ratio determines the effect on various symptoms of FMS. We included studies regarding the use of cannabinoids in the treatment of fibromyalgia, investigating the use of nabilone, dronabinol (a synthetic analog of THC), Bedrocan (22.4 mg THC, <1 mg CBD), Bediol (13.4 mg THC, 17.8 mg CBD), and Bedrolite (18.4 mg CBD, <1 mg THC). In the era of the coronavirus disease 2019 (COVID-19) pandemic and opioid crisis, many adverse outcomes are observed in the patients suffering from FMS due to lack of any definitive treatment and promising outcomes from the known treatment options, which led to the need for effective and safer treatment alternatives. Although the studies reviewed in this article suggest that medical cannabis is a safe and effective treatment for fibromyalgia pain, several limitations regarding dosage, length of treatment, adverse effects, long-term follow-up, and dependence needs further investigation.