Coupled reactions are reactions whose rate or equilibrium constant is not the same for the oxidized and reduced forms of the species that is being investigated. For example, reduction should favour protonation (): the protonation reaction is coupled to the reduction at . The binding of a small molecule (other than the proton) may also be coupled to a redox reaction.
Two cases must be considered depending on whether the coupled reaction is slow or fast (meaning that the time scale of the coupled reaction is larger or smaller than the voltammetric time scale ).
* Fast chemical reactions that are coupled to electron transfer (such as protonation) only affect the apparent values of  and , but the peaks remain symmetrical. The dependence of  on ligand concentration (e.g. the dependence of  on pH plotted in a Pourbaix diagram) can be interpreted to obtain the dissociation constants (e.g. acidity constants) from the oxidized or reduced forms of the redox species.
* Asymmetry may result from slow chemical reactions that are coupled to (and gate) the electron transfer. From fast scan voltammetry, information can be gained about the rates of the reactions that are coupled to electron transfer. The case of  and  reversible surface electrochemical reactions followed by irreversible chemical reactions was addressed by Laviron in refs but the data are usually interpreted using the numerical solution of the appropriate differential equations.