This review deals with mechanism and physiological activity of conjugated imine and iminium species, including those in the alkaloid category. An appreciable number can be found in the Merck Index. There is focus in mode of action on electron transfer (ET), reactive oxygen species (ROS), oxidative stress (OS) and reduction potential in the prior review. These aspects can be involved in both therapeutic action and toxicity. A unifying mechanistic approach involving ET-ROS-OS is applied to synthetic drugs and alkaloids in the imineiminium category in relation to both beneficial and adverse effects. Insight at the basic, molecular level can aid in practical pharmaceutical design.