Systematic reviews of randomized controlled trials of cannabinoid products in chronic pain conditions and for symptoms associated with multiple sclerosis: what do they tell us?

Introduction To investigate whether published systematic reviews of randomized controlled trials provide sufficient clarity to inform prescribing of medicinal cannabinoid products, we examined their features and findings in two well-researched areas: chronic cancer/noncancer pain and multiple sclerosis (MS)-related symptoms. Areas covered Structured searches from January 2011 to 2 February 2021 identified 31 systematic reviews (with/without meta-analyses) that met the inclusion criteria. Support for the efficacy of cannabinoids was minimal in cancer pain, and somewhat stronger in noncancer (especially neuropathic) pain and MS spasticity. All systematic reviews and most meta-analyses grouped cannabinoid products together without appropriate consideration of their differential attributes (active constituent(s), concentration/strength, dosage forms, administration route), dosing regimens or treatment durations. Patient populations and efficacy outcome measures were inhomogeneous, particularly for studies in noncancer pain and MS. Separate results for specific cannabinoid formulations were rarely provided. Expert opinion The therapeutic effect of cannabinoids, as already demonstrated for some products, is not reflected clearly in the current range of systematic reviews and meta-analyses in chronic pain and MS. To truly inform evidence-based practice, future publications should aim to present results by individual product from well-conducted clinical trials using appropriate and homogeneous outcome measures in well-defined patient populations.