This invention relates to deuterated forms of hexahydro-4,7-methano-1H-isoindole-1,3(2H)-diones, and pharmaceutically acceptable salts thereof. In one aspect, the invention provides a compound of Formula (I): or a pharmaceutically acceptable salt thereof. This invention also provides compositions comprising a compound of this invention, including pharmaceutical compositions comprising the compound and a pharmaceutically acceptable carrier. This invention also provides the use of such compounds and compositions in methods of treating diseases and conditions that are beneficially treated by administering a compounds that modulates the activity of a receptor selected from the group consisting of central dopamine Type 2 (D2) receptor and serotonin Type 2 (5HT2A) receptor. Some exemplary embodiments include a method of treating a disease or condition selected from schizophrenia and depressive episodes associated with bipolar I disorder, the method comprising the step of administering to a subject in need thereof a pharmaceutically acceptable composition of the present invention.