Since many folks with CH need as much as 960mg/day for verap to be effective, a 40mg tablet isn't going to be very helpful to you in any event. And certainly the effects on your heart should be monitored. Also, if you're doing D3, you have to be sure to take the calcium at an 8-hour separation from the verapamil, which is pretty difficult to arrange. Here's what one leading CH expert has written about verap:
Verapamil is more effective than placebo and compares favorably with lithium. Clinical practice clearly
supports the need to use relatively high doses for CH, certainly higher than those used in
cardiological indications. After obtaining a baseline EKG, start patients on 80 mg three times daily;
thereafter the total daily dose is increased in increments of 80 mg every 10-14 days. An EKG is
performed prior to each increment and at least ten days after the dose change. The dose is increased
until the cluster attacks are suppressed, side effects intervene or the maximum dose of 960 mg daily
is achieved. Side effects include constipation and leg swelling and gingival hyperplasia (patients must
monitor dental hygiene closely).