Provided are pharmaceutical compositions comprising (1 R,5S)-1-(naphthalen-2-yl)-3-azabicyclo[3.1.0]hexane, in free or pharmaceutically acceptable salt form. The compositions are formulated for providing a sustained release of enantiomerically pure (1 R,5S)-1 -(naphthalen-2-yl)-3-azabicyclo[3.1.O)hexane. The compositions are substantially free of the other (-) enantiomer of the compound.