The drug can be categorized as a serotonin–norepinephrine reuptake inhibitor (SNRI). These can be contrasted with the more widely used selective serotonin reuptake inhibitors (SSRIs) which act upon serotonin alone.
Individuals who are CYP2D6 poor metabolizers, mostly individuals with two copies from among the alleles CYP2D6*4, CYP2D6*5, and CYP2D6*6, are at risk for more side effects (p<0.005) in comparison with other patients. These side effects include gastrointestinal problems such as nausea, vomiting and diarrhea. However, the efficacy of venlafaxine was the same regardless of CYP2D6 genotype.[PMID 16958828]
SNPs that influence how well this drug works based on a patients genotype(s) include: