The drug partitioning between membrane and solution has traditionally been approached with bulk thermodynamic models, such as the octanol-water partitioning system. This neglects the orientational and compositional order in biological membranes. In the present study, electrochemistry at a Langmuir-Blodgett phospholipid monolayer-modified liquid-liquid interface has been employed to study the specific interactions between ionized drugs and phosphatidylcholine layers. To this end, AC voltammetric experiments and theoretical modeling accounting for the adsorption of the electroactive species have been carried out. The results point to a mechanism of charge transfer involving an adsorption step. This highlights the fact that in predicting biological activity of drugs, dynamic aspects and chemical interactions need to be considered.