Paulzen M, et al. - This study was performed to explore the pharmacokinetic interactions between venlafaxine and doxepin or mirtazapine in a naturalistic sample. An inhibiting effect of doxepin on the metabolism of venlafaxine was implied by higher concentrations of venlafaxine (VEN) and AM, even though the huge variability of concentrations had to be taken into account. Monitoring plasma concentrations in combination treatment were recommended to avoid problems in safety and efficacy.