**Cannabidiol Oral Solution (CBD-OS) Study for Focal-Onset Seizures** We're testing a medicine called Cannabidiol Oral Solution (CBD-OS) to see how well it works for people aged 12 to 75 years with focal-onset seizures (FOS). Focal-onset seizures start in one part of the brain. CBD-OS is already used for other types of seizures. This study checks if adding CBD-OS to other treatments can reduce seizures and improve health. We'll also look at how the body processes the medicine and its safety. **Eligibility:** To join, you must have focal epilepsy, be between 12 and 75 years old, and take 1-4 seizure medications. You can't join if you have other seizure types, unstable health issues, or are using cannabis products. **Key Points:** - **Study Length & Visits:** Participants will attend multiple visits for testing and monitoring. - **Safety & Side Effects:** The study will track any side effects and health changes. - **No Cannabis Use:** Participants must avoid cannabis products during the study. This research helps us understand how well CBD-OS works for seizures and ensures safety for all participants. Participation is voluntary and involves regular check-ups.