CYP2D6 Poor Metabolizer Status Tracks with Venlafaxine Treatment Failure in Two Real-World Cohorts

Venlafaxine Is a Common Second Step After SSRI Failure, but Genotype Outcome Data Have Been Limited

About half of patients do not respond adequately to a selective serotonin reuptake inhibitor (SSRI), making venlafaxine a common second-line option.¹ Pooled pharmacokinetic work has quantified how CYP2D6 status affects exposure to antidepressants.² Evidence linking these genotypes to venlafaxine outcomes remains limited. Guidelines, including those from the Clinical Pharmacogenetics Implementation Consortium, have not reached consensus on how CYP2D6 variation should shape venlafaxine prescribing.³ A two-cohort analysis explored how genotype predicts switching from venlafaxine in real-world practice.⁴

CYP2D6 Poor Metabolizers Switched from Venlafaxine More Often in Both Cohorts

The investigators used two retrospective samples: 5,443 adults genotyped through a Norwegian therapeutic drug monitoring service, and 3,624 UK Biobank participants prescribed venlafaxine in primary care. Treatment failure was defined as switching to another antidepressant within 1 year of last venlafaxine exposure. Switching occurred in 11.8% of the Norwegian sample and 31.7% of the UK sample. Risk estimates were adjusted for age, sex, and antidepressant polypharmacy. Compared with normal metabolizers, odds of switching were 2.05 times higher in poor CYP2D6 metabolizers (95% CI, 1.53-2.71; P<0.0001) in the Norwegian cohort and 1.58 times higher (95% CI, 1.14-2.19; P=0.006) in the UK cohort.⁴ Norwegian data also showed increased odds of switching in ultrarapid metabolizers (OR, 1.78; 95% CI, 1.06-2.83; P=0.021) and intermediate metabolizers (OR, 1.25; 95% CI, 1.05-1.50; P=0.014); neither pattern appeared in the UK data.

Prescribed Doses Shifted with Genotype Without Correcting the Metabolite Balance

Because poor metabolizers clear venlafaxine more slowly, prescribers often give them a lower dose, but the reported serum data show this does not correct the underlying imbalance between venlafaxine and its metabolite. In the Norwegian cohort, poor metabolizers were prescribed a geometric mean of 135.7 mg/day versus 149.7 mg/day in normal metabolizers (0.91-fold; P=0.0005). Serum data from 3,385 patients help explain why that may not suffice. Venlafaxine levels were 4.46 times higher in poor metabolizers compared to normal metabolizers, and O-desmethylvenlafaxine levels were 70% lower (P<0.0001 for each), while the active moiety differed by only 1.1-fold (P=0.0005).⁴ Prescribers gave poor metabolizers less venlafaxine, but that adjustment shifted total exposure only slightly and did not restore the normal balance between venlafaxine and its active metabolite

Outcome Evidence Has Arrived, But the Reasons for Switching Have Not

These retrospective, observational data show an association between CYP2D6 poor-metabolizer status and switching from venlafaxine into two independent cohorts, the kind of outcome evidence that has been lacking.  Switching is an indirect marker of treatment failure, however, and may have occurred because of intolerability, inadequate response, or other clinical decisions. Neither dataset consistently captured indication, comorbidity, or concomitant medication, so residual confounding cannot be excluded, and both samples were predominantly White. Prospective studies are needed to determine whether genotype-guided dosing or antidepressant selection reduces treatment failure in a cost-effective manner.⁴

References

1. Rush AJ, Trivedi MH, Wisniewski SR, et al. Bupropion-SR, sertraline, or venlafaxine-XR after failure of SSRIs for depression. N Engl J Med. 2006;354(12):1231-1242.
2. Milosavljevic F, Bukvic N, Pavlovic Z, et al. Association of CYP2C19 and CYP2D6 poor and intermediate metabolizer status with antidepressant and antipsychotic exposure: a systematic review and meta-analysis. JAMA Psychiatry. 2021;78(3):270-280.
3. Bousman CA, Stevenson JM, Ramsey LB, et al. Clinical Pharmacogenetics Implementation Consortium (CPIC) guideline for CYP2D6, CYP2C19, CYP2B6, SLC6A4, and HTR2A genotypes and serotonin reuptake inhibitor antidepressants. Clin Pharmacol Ther. 2023;114(1):51-68.
4. Park Y, Lenk HC, Zhou Y, Lauschke VM, Molden E. Association between CYP2D6 and CYP2C19 genotypes and venlafaxine treatment failure: a retrospective study on two cohorts from Norway and the UK. Lancet Psychiatry. 2026;13(10):852-860.