A multicomponent crystal (or co-crystal) comprising a first active pharmaceutical ingredient and a second active pharmaceutical ingredient. The multicomponent crystal is formed / sustained by non-covalent interactions between the nitrogen-containing heterocycle alpha-substituted with an amino group of the first active pharmaceutical ingredient and a carboxylic acid group of the second active pharmaceutical ingredient, suitably as well as other further non-covalent interactions with other H-bond forming groups. The multicomponent crystal may provide an improved multidrug dosage form comprising lamotrigine and valproic acid as the first and second active pharmaceutical ingredients, respectively. A pharmaceutical composition comprising a therapeutically effective amount of the multicomponent crystal and a pharmaceutically acceptable excipient, and a method of forming the multicomponent crystal, are also provided.
