I take verapamil. I am currently on 120mg 4 times a day (total 480mg per day). When I originally started on it, it was actually before I had CH and I was only taking 120mg or 240mg a day total - can't remember which. Once I started having CH and was diagnosed, we took the verapamil all the way up to 960mg a day. We first went up to 720mg pretty quickly - over about a week's time, I think - but then went up to 960mg later. My CH's had always come at the same time every day - 5pm, 7pm, 9pm, 11pm, 2am, and 4am - but ever since we first took the verap to 720mg, I no longer have CH at any regular schedule. This could be seen as a good or bad thing, but mostly I think it has been good.
Unfortunately, on the higher doses, my blood pressure got extremely low (60s/40s with pulse in the 40s), and I started having chest pains and vomiting, so we had to come down on the dose. For awhile I went to the short-acting form at 480mg a day, and then I dropped it altogether for awhile.
Last summer, I started back on it, and I've been on 480mg a day ever since then. I did have one abnormal EKG, but then we checked it again after a month, and it was normal, so we didn't have to adjust the dose - never knew if the abnormal EKG was from the verap or not. The biggest side effects the verap causes for me is fatigue and swollen feet. I don't have swollen feet all the time, but I get it periodically and it can be pretty bad. I actually have to talk to my neuro about this next week because it's been happening more frequently. The verapamil has reduced the amount of hits I had per day the majority of the time.
I had constipation from another med I'm on - and I'm not entirely sure if the verapamil made it worse or not. What worked for me was taking Miralax once a day. Miralax is now over the counter. I recently had surgery, and once again the constipation was an issue, so I tried Miralax and colace, and it worked once again. Once I got things more regular, the Miralax was able to be stopped. I'm also on domperidone for GI issues, which aids in gastric motility, so I don't know if that has the added benefit of reducing constipation also.
At any rate - that's my story with verap. I am a chronic CH'er for almost 5 years, and I've been on verapamil through most of it. Due to the recent surgery I had, I'm hoping to start weaning off all headache meds over the next few months, but that's another story, and the decision only came about after years of prolonged suffering with clusters and chronic daily migraine without relief.
Would your doc consider adding lithium to the verapamil instead of simply switching from verap to lithium? That works for a number of people here, and helped me for a little while, too!
Best of luck!
Carrie