This study will assess the efficacy of CBD-OS as an adjunctive treatment in reducing the frequency of focal seizures compared to baseline as well as the effect of CBD-OS on health outcome endpoints in early line and refractory participants with FOS. This study will also examine pharmacokinetics (PK), safety, and potential predictors or mediators of treatment response, including functional magnetic resonance imaging (fMRI) and neuropsychological testing in a substudy.