Calcium supplements: Do they interfere with blood pressure drugs?

Yes. In large amounts, calcium supplements may interfere with some blood pressure medications. Interactions may occur with the following blood pressure medications:

• Thiazide diuretics. Ingesting large amounts of calcium with thiazide diuretics — such as chlorothiazide, hydrochlorothiazide and indapamide — can result in milk-alkali syndrome, a serious condition characterized by excessively high levels of calcium and a shift in the body's acid-base balance to alkaline. In general, avoid consuming more than 1,500 milligrams of calcium (supplements and food sources combined) a day if you're taking a thiazide diuretic. If you do take calcium supplements while taking a thiazide diuretic, talk to your doctor about the appropriate dose and have your blood pressure and calcium levels monitored.
• Calcium channel blockers. When taken intravenously, calcium may decrease the effects of calcium channel blockers such as nifedipine, verapamil, diltiazem and others. In fact, intravenous calcium is used to help reverse calcium channel blocker overdose. However, there's no evidence that standard calcium supplements interfere with calcium channel blockers. To be safe, check your blood pressure regularly if taking calcium channel blockers and calcium supplements concurrently.

Calcium supplements don't appear to interact with other commonly prescribed blood pressure medications, such as beta blockers, angiotensin-converting enzyme (ACE) inhibitors, angiotensin II receptor blockers or renin inhibitors. Talk to your doctor if you take high blood pressure medications and calcium supplements and are concerned about interactions.