The tolerability and safety of venlafaxine hydrochloride, a new serotonin and norepinephrine reuptake inhibitor, are reviewed in this article. The data presented here are based on a pool of 3,082 patients who were treated with this agent during clinical trials. Of these patients, 2,897 received venlafaxine for depression; 455 of these patients were treated for more than 360 days. The tolerability and safety profiles of venlafaxine were similar to those previously reported for selective serotonin reuptake inhibitors. Patients receiving venlafaxine experienced nausea, insomnia, dizziness, somnolence, constipation, and sweating more often than did patients receiving placebo but reported anticholinergic events less frequently than did patients receiving tricyclics. This is accounted for by the fact that, unlike the tricyclics, venlafaxine lacks significant affinity for muscarinic cholinergic receptors. Resolution of venlafaxine-associated nausea occurred rapidly in the vast majority of the patients who reported it at the start of therapy. Serious adverse events were rare among venlafaxine-treated patients. A small percentage of the patients given venlafaxine experienced modest but significant increases in blood-pressure readings, similar to those observed among imipramine-treated patients. At mean daily venlafaxine dosages of up to 300 mg, the percentage of venlafaxine-treated patients who had sustained elevations in supine diastolic blood pressure during treatment ranged from 2% to 6%, compared with 2% and 5% among the placebo- and imipramine-treated patients, respectively. All of the 14 patients who took an overdose of venlafaxine recovered without sequelae. Tolerability and safety in the elderly did not differ significantly from that observed in younger patients.