The efficacy of venlafaxine hydrochloride extended-release capsules as a treatment for Major Depressive Disorder (MDD) was established in two placebo-controlled, short-term (8 weeks for study 1; 12 weeks for study 2), flexible-dose studies, with doses starting at 75 mg per day and ranging to 225 mg per day in adult outpatients meeting DSM-III-R or DSM-IV criteria for MDD. In moderately depressed outpatients, the initial dose of venlafaxine was 75 mg per day. In both studies, venlafaxine hydrochloride extended-release capsules demonstrated superiority over placebo on the primary efficacy measure defined as change from baseline in the HAM-D-21 total score to the endpoint visit, venlafaxine hydrochloride extended-release capsules also demonstrated superiority over placebo on the key secondary efficacy endpoint, the Clinical Global Impressions (CGI) Severity of Illness scale. Examination of gender subsets of the population studied did not reveal any differential responsiveness on the basis of gender.

A 4-week study of inpatients meeting DSM-III-R criteria for MDD with melancholia utilizing venlafaxine hydrochloride in a range of 150 to 375 mg per day (divided in a three-times-a-day schedule) demonstrated superiority of venlafaxine hydrochloride over placebo based on the HAM-D-21 total score. The mean dose in completers was 350 mg per day (study 3). 

In a longer-term study, adult outpatients with MDD who had responded during an 8-week open-label study on venlafaxine hydrochloride extended-release capsules (75, 150, or 225 mg, once daily every morning) were randomized to continuation of their same venlafaxine hydrochloride extended-release capsules dose or to placebo, for up to 26 weeks of observation for relapse. Response during the open-label phase was defined as a CGI Severity of Illness item score of ≤3 and a HAM-D-21 total score of ≤10 at the day 56 evaluation. Relapse during the double-blind phase was defined as follows: (1) a reappearance of major depressive disorder as defined by DSM-IV criteria and a CGI Severity of Illness item score of ≥4 (moderately ill), (2) 2 consecutive CGI Severity of Illness item scores of ≥4, or (3) a final CGI Severity of Illness item score of ≥4 for any patient who withdrew from the study for any reason. Patients receiving continued venlafaxine hydrochloride extended-release capsules treatment experienced statistically significantly lower relapse rates over the subsequent 26 weeks compared with those receiving placebo (study 4). 

In a second longer term trial, adult outpatients with MDD, recurrent type, who had responded (HAM-D-21 total score ≤12 at the day 56 evaluation) and continued to be improved [defined as the following criteria being met for days 56 through 180: (1) no HAM-D-21 total score ≥20; (2) no more than 2 HAM-D-21 total scores >10, and (3) no single CGI Severity of Illness item score ≥4 (moderately ill)] during an initial 26 weeks of treatment on venlafaxine hydrochloride [100 to 200 mg per day, on a twice daily schedule] were randomized to continuation of their same venlafaxine hydrochloride dose or to placebo. The follow-up period to observe patients for relapse, defined as a CGI Severity of Illness item score ≥4, was for up to 52 weeks. Patients receiving continued venlafaxine hydrochloride treatment experienced statistically significantly lower relapse rates over the subsequent 52 weeks compared with those receiving placebo (study 5).