Calcium supplements can REDUCE the effectiveness of calcium channel blockers.
Calcium is needed for cardiac and vascular smooth muscles to contract. Calcium channel blocking drugs work by reducing the amount of calcium available to heart and vascular tissues.
So some people are concerned that oral calcium supplements could possibly counteract the therapeutic benefits of calcium channel blockers. However, there is no data to support this theory.
It is true that calcium is sometimes helpful in the management of calcium channel blocker overdose. And it has also been used to reduce the hypotensive effects of verapamil when used to treat arrhythmias.