At Week 0 of Second Phase (maintenance therapy) Has improved/stabilised during the First Phase (titration) as indicated by a CGI-S score of ≤3 (mildly ill). Once improved, the subject must also demonstrate sustained improvement by achieving a CGI-S score of ≤3 (mildly ill) for at least 4 consecutive weeks of treatment immediately prior to the Second Phase (maintenance therapy) (randomization).