<p>The electrochemical behavior of catecholamines involves an electron transfer-chemical reaction-electron transfer (ECE) mechanism, characterized by two reversible redox reactions interspersed with an irreversible chemical reaction. Previously, we reported ECE studies on dopamine and norepinephrine. In this work, we extend our study to catecholamine drugs including dobutamine, isoprenaline, droxidopa, and methyldopa, using a carbon nanotube electrode. These drugs exhibit significantly faster intramolecular cyclization rates compared to dopamine and norepinephrine. This accelerated cyclization is attributed to (1) the presence of more complex substituents in these drugs and (2) the fact that dobutamine and isoprenaline are secondary amines, while dopamine and norepinephrine are primary amines. This study enhances the understanding of catecholamines and offers valuable insights for the development of novel electrochemical sensing strategies for catecholamine drugs.</p> Graphical abstract <p></p>