The present invention relates to a 9-azabicyclo[3.3.1]nonane derivative of formula (I), wherein R1 is H or C1-5alkyl; X is O or NR2, wherein R2 is H, C1-5alkyl or C2-5acyl and Ar is C6-10aryl or a 5-10 membered heteroaryl ring system, both being optionally substituted with one to three of R3-R5 independently selected from halogen, C1-5alkyl, C1-5alkoxy, C3-6cycloalkyl, C2-5alkenyl, C2-5alkynyl, CN, NO2, hydroxy, phenyl, phenoxy and phenylC1-2alkoxy, wherein said C1-5alkyl and C1-5alkoxy are optionally substituted with one to three halogens and wherein said phenyl, phenoxy and phenylC1-2alkoxy are optionally substituted with one to three substituents independently selected from halogen and methyl or two of R3-R5 at adjacent positions together form a methylenedioxy or propylene unit, with the proviso that the compounds exo-9-methyl-3-phenoxy-9-azabicyclo[3.3.1]nonane and N-(9-methyl-9-azabicyclo[3.3.1]non-3-yl)-1H indazole-5-amine are excluded, or a pharmaceutically acceptable salt or solvate thereof. The invention also relates to pharmaceutical compositions comprising said 9-azabicyclo[3.3.1]nonane derivatives and to their use in therapy.