Quote from beerzoids:

I had a problem with Verapamil. In 2003, my insurance provider switched to a different manufacturer of the generic Verapamil. I started noticing that the Verapamil just wasn't working as well as before, but I thought that I was just becoming resistant to the Verapamil.

In 2004, my insurance provider switched back to the original manufacturer and BOOM, the Verapamil kicked in just as effective as it had done before.

I used to take Verapamil too. I took the brand name Calan. It worked for a few years and all of a sudden it seemd to quit working as well. That was when I was switched to Cardiazem. I wish I could still take either of those CCBs. They both worked good for me.
Cass