Tentative evidence supports the use of verapamil topically to treat plantar fibromatosis. Contraindications
Use of verapamil is generally avoided in people with severe left ventricular dysfunction, hypotension (systolic blood pressure less than 90 mm Hg), cardiogenic shock, and hypersensitivity to verapamil. It is also contraindicated in people with atrial flutter or fibrillation and an existing accessory tract such as in Wolff-Parkinson-White syndrome. Side effects
The most common side effect of verapamil is constipation (7.3%). While the definite mechanism by which Verapamil causes constipation has not been studied, studies have been conducted to rule out mechanisms of actions that might yield this adverse effect. In a study conducted by  The National Library of Medicine titled, "Effect of Verapamil on the Human Intestinal Transit", the study found that verapamil does not have an effect on upper GI transit but rather in the colon.Other side effects include dizziness (3.3%), nausea (2.7%), low blood pressure (2.5%), and headache 2.2%. Other side effects seen in less than 2% of the population include: edema, congestive heart failure, pulmonary edema, fatigue, elevated liver enzymes, shortness of breath, low heart rate, atrioventricular block, rash and flushing. Along with other calcium channel blockers, verapamil is known to induce gingival enlargement. Overdose
Acute overdose is often manifested by nausea, weakness, slow heart rate, dizziness, low blood pressure, and abnormal heart rhythms. 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.
Uses in cell biology
Verapamil inhibits the ATP-binding cassette (ABC) transporter family of proteins found in stem cells and has been used to study cancer stem cells (CSC) within head and neck squamous cell carcinomas.Verapamil is also used in cell biology as an inhibitor of drug efflux pump proteins such as P-glycoprotein and other ABC transporter proteins. This is useful, as many tumor cell lines overexpress drug efflux pumps, limiting the effectiveness of cytotoxic drugs or fluorescent tags. 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. See also
Gallopamil
Tiapamil

References
External links
"Verapamil". Drug Information Portal. U.S. National Library of Medicine. "Verapamil hydrochloride". Drug Information Portal. U.S. National Library of Medicine.