According to the results of in vitro studies and studies on healthy volunteers, terbinafine slightly inhibits or increases the clearance rate of most drugs metabolized by cytochrome P450 system (such as cyclosporine, terfenadine, triazoles, p-toluenesulfonylurea or oral contraceptives).

However, in vitro studies show that terbinafine inhibits CYP2D6-mediated metabolism, which may be related to those compounds that are mainly metabolized by CYP2D6 in clinic, such as tricyclic antidepressants (TCAs), β-blockers, selective serotonin reuptake inhibitors (SSRIs) and monoamine oxidase inhibitors (MAO-IS) type B, because they also have narrow therapeutic windows. It is reported that patients taking terbinafine combined with oral contraceptives have irregular menstruation, although the incidence rate is still within the range of patients taking oral contraceptives alone. On the other hand, some metabolic drugs (such as rifampicin) can accelerate the plasma clearance of terbinafine, while others (such as cimetidine) can inhibit the plasma clearance of terbinafine. If it is necessary to use these drugs simultaneously, the dose of terbinafine should be adjusted accordingly.