Verapamil is a medical drug that acts as a calcium channel blocker. It is used in the treatment of hypertension, angina pectoris, and some types of arrhythmia.

Verapamil is a class IV antiarrhythmic agent, and decreases conduction through the AV node.

Some possible side effects of the drug are headaches, facial flushing, dizziness, swelling, and constipation.

International alternative (brand) name: Isoptin

Verapamil is also used in cell biology as an inhibitor of drug efflux pump proteins such as P-Glycoprotein. This is useful as many tumor cell lines overexpress drug efflux pumps, limiting the effectiveness of cytotoxic drugs or fluorescent probes. Its also used in fluorescent cell sorting for DNA content, as it blocks efflux of a variety of DNA-binding fluorochromes such as Hoechst 33342. Source: Annu Rev Pharmacol Toxicol. 1996;36:161-8. P-glycoproteins and multidrug resistance. Bellamy WT.