Effexor Drug Classification
Effexor (venlafaxine) is a serotonin-norepinephrine reuptake inhibitor (SNRI), a class of antidepressant that inhibits the presynaptic reuptake of both serotonin and norepinephrine. 1, 2
Mechanism of Action
Venlafaxine blocks the reuptake of both serotonin (5-HT) and norepinephrine with a 30-fold selectivity for serotonin over norepinephrine. 3
At lower therapeutic doses, venlafaxine primarily inhibits serotonin reuptake, while at higher therapeutic doses (typically above 150 mg/day), it inhibits both serotonin and norepinephrine reuptake. 4
This dual mechanism distinguishes venlafaxine from selective serotonin reuptake inhibitors (SSRIs), which only affect serotonin reuptake. 1
Key Distinguishing Features from Other Antidepressants
Unlike tricyclic antidepressants (TCAs), venlafaxine lacks significant activity at muscarinic cholinergic, H1 histaminergic, and alpha-1 adrenergic receptors, resulting in a side-effect profile more similar to SSRIs. 5
The SNRI classification is clinically important because it differentiates venlafaxine from SSRIs in treatment algorithms for conditions like social anxiety disorder and generalized anxiety disorder. 1
Venlafaxine shares its SNRI classification with duloxetine and milnacipran, though these medications should never be combined due to the significant risk of serotonin syndrome. 2
Clinical Implications of SNRI Classification
The norepinephrine reuptake inhibition component contributes to efficacy in chronic pain conditions, particularly neuropathic pain, which distinguishes SNRIs from SSRIs that are generally ineffective for chronic pain. 3
The dual mechanism requires monitoring for noradrenergically-mediated side effects including dose-dependent blood pressure elevation (particularly at doses >225 mg/day), dry mouth, and constipation. 2, 6, 3
Blood pressure and pulse must be measured regularly when prescribing venlafaxine, especially at higher doses, due to its norepinephrine effects. 6