The main purpose of this study is to determine if XEN1101 can reduce the seizure frequency and if it is safe to use. XEN1101 has been tested in other studies in epilepsy patients and it was considered to be well-tolerated. It had side effects that are similar to other antiseizure drugs commonly used to help patients with epilepsy.

XEN1101 is considered investigational, which means it is not yet approved by the U.S. Food and Drug Administration (FDA). 

Participants will be randomized to receive either XEN1101 or placebo. The study will compare XEN1101 to a placebo to see if XEN1101 is safe and works better than the placebo.

Study visits are required at 1 week, 2 weeks, 4 weeks, 8 weeks, and 12 weeks, as well as two follow-up visits at 13 and 20 weeks. These visits will include any combination of neurological surveys and assessments, blood draws, and/or a 12-lead ECG. Within the initial screening period, 12-week visit, and follow-up visit, participants can expect to undergo an ophthalmology exam as well. 

The total study length is 9.5 weeks of screening and if eligible, 20 weeks in the study. At the end of the study, and/or during the last study visits, participants will have the option to enroll in the ancillary open-label study of this trial.