Constipation is a common side effect of verapamil treatment.¹ Increasing fluid and fiber intake can ease constipation.

Vitamin D may interfere with the effectiveness of verapamil.² People taking verapamil should ask their doctor before using vitamin D-containing supplements.

Grapefruit juice may increase verapamil blood levels.³ The importance of this interaction regarding verapamil effectiveness and side effects is unknown. Until more is known, it makes sense for people taking this drug to either avoid drinking grapefruit juice entirely or drink grapefruit juice only under the careful monitoring and supervision of the prescribing doctor. In theory, this last possibility might allow for a decrease in drug dose, but it could be dangerous in the absence of diligent monitoring. The same effects might be seen from eating grapefruit as from drinking its juice.

As pleurisy root and other plants in the Aesclepius genus contain cardiac glycosides, it is best to avoid use of pleurisy root with heart medications such as calcium channel blockers.⁴

Pomegranate juice has been shown to inhibit the same enzyme that is inhibited by grapefruit juice.^{5 , 6} The degree of inhibition is about the same for each of these juices. Therefore, it would be reasonable to expect that pomegranate juice might interact with verapamil in the same way that grapefruit juice does.