Provided are tryptophan-2,3-dioxygenase (TDO) and/or indoleamine-2,3-dioxygenase (IDO) inhibitor compounds I [ X¹, X², X³, X⁴, X⁵ = C, N, O,; each atom having a dotted line may independently have a double bond or a single bond, provided that valencies at each atom are maintained; R¹, R², R³, R⁴, R⁵, R⁷= present or absent and may be the same or different and is selected from H, (un)substituted 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, (un)substituted 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 sulfonyl 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], for the treatment of various diseases.