Assessment of Adjunctive Cannabidiol Oral Solution (GWP42003-P) in Children With Tuberous Sclerosis Complex (TSC), Dravet Syndrome (DS), or Lennox-Gastaut Syndrome (LGS) Who Experience Inadequately-controlled Seizures

Key Inclusion Criteria:

• Participants with TSC (1 month to < 2 years of age), or DS (1 year to < 2 years ofage), or LGS (1 year to < 2 years of age) within the specified age range at the timeof initial informed consent.

• Parent(s)/legal representative is/are willing and able to give informed consent forparticipation in the study.

• Parent(s)/legal representative is/are willing and able (in the investigator'sopinion) to comply with all study requirements (including accurate electronicparticipant-reported outcome [ePRO] diary completion).

• Participants with TSC must have a diagnosis per the 2012 International TuberousSclerosis Complex Consensus Conference. Participants with LGS or DS must have adiagnosis that is consistent with International League Against Epilepsy (ILAE)guidelines and confirmed by the Epilepsy Study Consortium (ESCI).

• Participants who have uncontrolled seizures, and who are currently receiving 1 ormore antiseizure medication (ASMs).

• A suitable VEEG, as available in the medical record, within 1 year of Visit 1. Whena historical VEEG is not available, and if clinically indicated and appropriate (dueto uncertainties or new seizures), a VEEG will be completed and read to confirmdiagnosis prior to Visit 3. All VEEGs are to be read at baseline by the investigatorand by an independent reviewer.

• Has seizures which are not adequately controlled through their current ASMs, definedas ≥ 1 seizure reported on the seizure diary during the screening/baseline period

Key Exclusion Criteria:

• Has tumor growth which, in the opinion of the investigator, could affect participantsafety.

• Has clinically significant abnormal laboratory values, in the investigator'sopinion, at screening/baseline.

• Has clinically significant abnormalities in the electrocardiogram (ECG) measured atscreening/baseline.

• Has any concurrent cardiovascular conditions, that will, in the investigator'sopinion, interfere with the ability to assess their ECGs.

• Has any known or suspected hypersensitivity to cannabinoids or any of the excipientsof the study intervention such as sesame seed oil.

• Has significantly impaired hepatic function prior to Visit 3, defined as:

• Serum alanine aminotransferase (ALT) or aspartate aminotransferase (AST) > 3 ×upper limit of normal (ULN) and (total bilirubin [TBL] > 2 × ULN orinternational normalized ratio [INR] > 1.5).

• Serum ALT or AST > 5 × ULN.

• Serum ALT or AST > 3 × ULN with the presence of fatigue, nausea, vomiting,right upper quadrant pain or tenderness, fever, rash, and/or eosinophilia (> 5%).

• Elevated ALT or AST should be discussed with the medical monitor prior to Visit 3; the medical monitor may allow for a confirmatory re-draw prior to Visit 3.

• Has received another study intervention within 4 weeks prior to Visit 1 or plans totake another study intervention during the study.

• Has any other clinically significant disease or disorder which, in the opinion ofthe investigator, may either put the participant, other participants, or site staffat risk because of participation in the study, may influence the result of thestudy, or may affect the participant's ability to take part in the study.

• Any clinically significant abnormalities identified following a physical examinationof the participant that, in the opinion of the investigator, would jeopardize thesafety of the participant if they took part in the study.

• Has previously been enrolled into this study.

• Has plans to travel outside their country of residence during the study, unless theparticipant has confirmation that the study intervention is permitted in thedestination country.

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.