This cohort study aims to assess the outcomes of fibromyalgia patients enrolled in the UK Medical Cannabis Registry prescribed a homogenous selection of cannabis-based medicinal products (CBMPs). A cohort study of fibromyalgia patients treated with oils (Adven®, Curaleaf International, UK), dried flower (Adven®, Curaleaf International, UK) or both CBMPs was performed. Primary outcomes were changes from baseline at 1, 3, 6 and 12 months in validated patient-reported outcome measures. Secondary outcomes included descriptive analysis of adverse events. One hundred and forty-eight participants were treated with oils (n = 77; 52.03%), dried flower (n = 14; 9.46%) or both (n = 57; 38.51%). Improvements in the generalized anxiety disorder-7 questionnaire, single-item sleep quality scale, fibromyalgia symptom severity score and EQ-5D-5L Index values were observed at each follow up period compared to baseline (p < 0.050). Thirty-six (24.32%) patients experienced 648 adverse events. Improvements were observed across all primary outcomes with no differences observed across different formulations of CBMPs. Adverse events were reported by one-quarter of participants and were more likely to reported by cannabis naïve patients. This present work through focusing on a homogeneous group of CBMPs can help inform randomized controlled trials after observing signals of improvement associated with a specific cultivar of CBMPs.