Provided is a tryptophan-2, 3-dioxygenase (TDO) and/or indoleamine-2, 3-dioxygenase (IDO) inhibitor compound for use in medicine, which compound comprises the following formula : wherein X1, X2, X3, X4, and X5 may be the same or different and each is independently selected from C, N and O; each atom having a dotted line may independently have a double bond or a single bond, provided that valencies at each atom arc maintained; each R1, R2, R3, R4, and R7 may be present or absent and may be the same or different and is selected from H and a substituted or unsubstituted organic group, provided that the number of such R groups present is such that the valencies of X1, X2, X3, X4, and X5 are maintained; one or two R6 groups may be present and are selected from H and a substituted or unsubstituted organic group, provided that the number of R6 groups present is such that the valency of the carbon atom to which they are attached is maintained, and provided that at least one R6 is an organic group comprising an atom double-bonded to an oxygen atom (preferably a carbonyl group or a sulphonyl group) at an α-, β-, or γ-position to the carbon atom to which the R6 is attached and in which the atom double-bonded to an oxygen atom is also bonded to a hetero-atom.