Verapamil is a FDA approved drug used to treat high blood pressure and to control chest pain. Verapamil is an L-type calcium channel blocker that also has antiarrythmic activity. The R-enantiomer is more effective at reducing blood pressure compared to the S-enantiomer. However, the S-enantiomer is 20 times more potent than the R-enantiomer at prolonging the PR interval in treating arrhythmias. Verapamil inhibits voltage-dependent calcium channels. Specifically, its effect on L-type calcium channels in the heart causes a reduction in ionotropy and chronotropy, thuis reducing heart rate and blood pressure. Verapamil's mechanism of effect in cluster headache is thought to be linked to its calcium-channel blocker effect, but which channel subtypes are involved is presently not known.

Dexverapamil (R-verapamil) is an enantiomer of verapamil. R-isomer behaved as an inhibitor of multidrug-resistant protein MRP1 (involved in the cancer cell multidrug resistance phenotype). It was developed by Knoll (BASF Pharma) as a chemosensitiser and/or modulator of multidrug resistance for use in combination with cancer chemotherapy. Dexverapamil was undergoing phase II clinical studies in France, Italy, Spain, United Kingdom and the US in patients with various cancers. It was also undergoing phase I clinical trials in Japan where it was licensed to Mitsui and Mitsui Toatsu Chemicals. However, development was discontinued. Dexverapamil (R-verapamil) has been developing by AGI therapeutics for the treatment of Irritable bowel syndrome however development was discontinued.