Tricyclic dibenzothiazepine compounds for use in the treatment of CDKL5 disorder. Specifically, a compound of Formula I, or a pharmaceutically or veterinarily acceptable salt thereof, or a pharmaceutically or veterinarily acceptable solvate of either entity for use in the treatment of CDKL5 disorder in a mammal, wherein a compound of Formula I comprises: (i) formula 1 or a pharmaceutically or veterinarily acceptable salt thereof, or a pharmaceutically or veterinarily acceptable solvate of either entity, wherein: R