[9] Common side effects include headache, low blood pressure, nausea, and constipation.

[15][16] Verapamil is used for controlling ventricular rate in supraventricular tachycardia (SVT) and migraine headache prevention.

[24] Use of verapamil in people with recent onset of type 1 diabetes may improve pancreatic beta cell function.

In a 2023 meta-analysis[25] involving data from two randomized controlled trials (113 patients with recent onset type-1 diabetes), it was demonstrated that the use of verapamil over one year was associated with significantly higher C-peptide area under the curve levels.

Higher C-peptide levels means better pancreatic insulin production and beta cell function.

[4] It is also contraindicated in people with atrial flutter or fibrillation and an existing accessory tract such as in Wolff-Parkinson-White syndrome.

Other side effects seen in less than 2% of the population include: edema, congestive heart failure, pulmonary edema, diarrhea, fatigue, elevated liver enzymes, shortness of breath, low heart rate, atrioventricular block, rash and flushing.

Plasma, serum, or blood concentrations of verapamil and norverapamil, its major active metabolite, may be measured to confirm a diagnosis of poisoning in hospitalized patients or to aid in the medicolegal investigation of fatalities.

Blood or plasma verapamil concentrations are usually in a range of 50–500 μg/L in persons on therapy with the drug, but may rise to 1–4 mg/L in acute overdose patients and are often at levels of 5–10 mg/L in fatal poisonings.

By relaxing the tone of this smooth muscle, calcium channel blockers dilate the blood vessels.

[4] Preventive therapy with verapamil is believed to work because it has an effect on the circadian rhythm and on CGRPs, as CGRP-release is controlled by voltage-gated calcium channels.

Verapamil can be given postoperatively in rabbits which have suffered trauma to abdominal organs to prevent formation of these adhesions.

It is also used in fluorescent cell sorting for DNA content, as it blocks efflux of a variety of DNA-binding fluorophores such as Hoechst 33342.

Radioactively labelled verapamil and positron emission tomography can be used with to measure P-glycoprotein function.