Venlafaxine (brand name: Effexor or Efexor) is a bicyclic antidepressant and is usually categorized as a serotonin-norepinephrine reuptake inhibitor (SNRI), but it has been referred to as a serotonin-norepinephrine-dopamine reuptake inhibitor. It works by blocking the transporter reuptake proteins for key neurotransmitters affecting mood, thereby leaving more active neurotransmitter in the synapse. The neurotransmitters affected are serotonin (5-hydroxytryptamine) and norepinephrine (noradrenaline). Additionally, in high doses, it weakly inhibits the reuptake of dopamine. A comparison of adverse event rates in a fixed-dose study comparing venlafaxine 75, 225, and 375 mg/day with placebo revealed a dose dependency for some of the more common adverse events associated with venlafaxine use. The rule for including events was to enumerate those that occurred at an incidence of 5% or more for at least one of the venlafaxine groups and for which the incidence was at least twice the placebo incidence for at least one venlafaxine group. Tests for potential dose relationships for these events (Cochran-Armitage Test, with a criterion of exact 2-sided p-value <= 0.05) suggested a dose-dependency for several adverse events in this list, including chills, hypertension, anorexia, nausea, agitation, dizziness, somnolence, tremor, yawning, sweating, and abnormal ejaculation (Wyeth Monograph). Venlafaxine is an effective anti-depressant for many persons; however, it seems to be especially effective for those with treatment-resistant depression. Patients suffering from severe long-term depression typically respond better to venlafaxine than other drugs. However, venlafaxine has been reported to be more difficult to discontinue than other antidepressants. In addition, a September 2004 Consumer Reports study ranked venlafaxine as the most effective among six commonly prescribed antidepressants. However, this should not be considered a definitive finding, since responses to psychiatric medications can vary significantly from individual to individual. A black box warning has been issued with venlafaxine and with other SSRI and SNRI anti-depressants advising of risk of suicide. There is an additional risk if a physician misinterprets patient expression of adverse effects such as panic or akathisia. Careful assessment of patient history and comorbid risk factors such as drug abuse are essential in evaluating the safety of venlafaxine for individual patients. Another risk is serotonin syndrome. This is a serious effect that can be caused by interactions with other drugs and is potentially fatal. This risk necessitates clear information to patients and proper medical history. Venlafaxine is used primarily for the treatment of depression, generalized anxiety disorder, obsessive-compulsive disorder, social anxiety disorder, and panic disorder in adults. It is also used for other general depressive disorders. Although it is not approved for use in children or adolescents, there is considerable information by Wyeth on cautions if prescribed to this age group. Venlafaxine hydrochloride is a prescription antidepressant first introduced by Wyeth in 1993. As of August 2006, generic venlafaxine is available in the United States.