Provided is a tryptophan-2, 3-dioxygenase (TDO) and/or indoleamine-2, 3-dioxygenase (IDO) inhibitor compound for use in medicine, which compound comprises formula (I) wherein X1, and X2 may be the same or different and each is independently selected from C, N, O and S; X3, X4, X5, and X6 may be the same or different and each is independently selected from C and N; each bond represented by a dotted line may be present or absent, provided that at least one such bond is present; R1, R2, R3, R4, R5 and R6 may be present or absent and may be the same or different and each is independently selected from H and a substituted or unsubstituted organic group, provided that the number of R1, R2, R3, R4, R5 and R6 groups present is such that the respective valencies of X1, X2, X3, X4, X5, and X6 are maintained; and wherein at least one of R5 and R6 comprises a group Y, wherein Y is a group having a formula selected from (II), (III), (IV), (V), (VI), (VII) wherein L may be present or absent, and may be a substituted or unsubstituted organic linking group; R31 and R32 may be the same or different and are selected from H and a substituted or unsubstituted organic group; each R34 may be the same or different and is selected from H and a substituted or unsubstituted organic group; R35 is selected from a substituted or unsubstituted alcohol group or ether group; each R36 may be the same or different and is selected from H and a substituted or unsubstituted organic group; X7 may be selected from C and N; X8, X9, X10, X11, X12, X13, X14, X15 and X16 may be the same or different and each is independently selected from C, N, O and S; each bond represented by a dotted line may be present or absent; and each R313 may be the same or different and is selected from H and a substituted or unsubstituted organic group.