A compound of Formula 1, Formula 2 or Formula 3 or a solvate, tautomer, or pharmaceutically acceptable salt thereof, for use in the treatment or control of medical conditions and diseases that are treatable or controllable by inhibiting interferon gamma (IFN-γ) production, which medical conditions and disease are selected from prion diseases, rheumatoid arthritis, inflammatory bowel disease, autoimmune skin diseases, psoriasis, Sjögren's syndrome, Crohn's disease, and type 1 diabetes mellitus: in which: A is selected from; i. a phenyl ring substituted with up to five substituents, R c, each independently selected from halogen atoms, haloalkyl groups having from 1 to 4 carbon atoms, alkoxy groups having from 1 to 4 carbon atoms, and haloalkoxy groups having from 1 to 4 carbon atoms; and ii. a thiophene ring optionally substituted with up to three substituents, R c, each selected independently from halogen atoms, alkyl groups having from 1 to 4 carbon atoms, haloalkyl groups having from 1 to 4 carbon atoms, alkoxy groups having from 1 to 4 carbon atoms and haloalkoxy groups having from 1 to 4 carbon atoms; and iii. a C(R d) 3 group, wherein each R d is independently selected from hydrogen, alkyl groups having from 1 to 4 carbon atoms, and phenyl rings optionally substituted with up to five substituents, each independently selected from halogen atoms, alkyl groups having from 1 to 4 carbon atoms, haloalkyl groups having from 1 to 4 carbon atoms, alkoxy groups having from 1 to 4 carbon atoms, and haloalkoxy groups having from 1 to 4 carbon atoms, and wherein at least two R d groups are optionally substituted phenyl rings; R a is selected from hydrogen, haloalkyl groups having from 1 to 4 carbon atoms, and alkyl-alkoxy groups having from 1 to 6 carbon atoms that are optionally substituted with one or more halogen atoms, with the proviso that when A is a phenyl ring comprising one or more directly bound halogen substituents, the compound is of Formula 2 or 3, and R a is not hydrogen; each R b is independently selected from hydrogen, alkyl groups having from 1 to 4 carbon atoms, and haloalkyl groups having from 1 to 4 carbon atoms. A is selected from; i. a phenyl ring substituted with up to five substituents, R c, each independently selected from halogen atoms, haloalkyl groups having from 1 to 4 carbon atoms, alkoxy groups having from 1 to 4 carbon atoms, and haloalkoxy groups having from 1 to 4 carbon atoms; and ii. a thiophene ring optionally substituted with up to three substituents, R c, each selected independently from halogen atoms, alkyl groups having from 1 to 4 carbon atoms, haloalkyl groups having from 1 to 4 carbon atoms, alkoxy groups having from 1 to 4 carbon atoms and haloalkoxy groups having from 1 to 4 carbon atoms; and iii. a C(R d) 3 group, wherein each R d is independently selected from hydrogen, alkyl groups having from 1 to 4 carbon atoms, and phenyl rings optionally substituted with up to five substituents, each independently selected from halogen atoms, alkyl groups having from 1 to 4 carbon atoms, haloalkyl groups having from 1 to 4 carbon atoms, alkoxy groups having from 1 to 4 carbon atoms, and haloalkoxy groups having from 1 to 4 carbon atoms, and wherein at least two R d groups are optionally substituted phenyl rings; i. a phenyl ring substituted with up to five substituents, R c, each independently selected from halogen atoms, haloalkyl groups having from 1 to 4 carbon atoms, alkoxy groups having from 1 to 4 carbon atoms, and haloalkoxy groups having from 1 to 4 carbon atoms; and ii. a thiophene ring optionally substituted with up to three substituents, R c, each selected independently from halogen atoms, alkyl groups having from 1 to 4 carbon atoms, haloalkyl groups having from 1 to 4 carbon atoms, alkoxy groups having from 1 to 4 carbon atoms and haloalkoxy groups having from 1 to 4 carbon atoms; and iii. a C(R d) 3 group, wherein each R d is independently selected from hydrogen, alkyl groups having from 1 to 4 carbon atoms, and phenyl rings optionally substituted with up to five substituents, each independently selected from halogen atoms, alkyl groups having from 1 to 4 carbon atoms, haloalkyl groups having from 1 to 4 carbon atoms, alkoxy groups having from 1 to 4 carbon atoms, and haloalkoxy groups having from 1 to 4 carbon atoms, and wherein at least two R d groups are optionally substituted phenyl rings; R a is selected from hydrogen, haloalkyl groups having from 1 to 4 carbon atoms, and alkyl-alkoxy groups having from 1 to 6 carbon atoms that are optionally substituted with one or more halogen atoms, with the proviso that when A is a phenyl ring comprising one or more directly bound halogen substituents, the compound is of Formula 2 or 3, and R a is not hydrogen; each R b is independently selected from hydrogen, alkyl groups having from 1 to 4 carbon atoms, and haloalkyl groups having from 1 to 4 carbon atoms.