Calcium Supplements and High Blood Pressure Medications

Nurse checking patients blood pressure in examination room.
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Calcium supplements are generally safe and are not likely to affect your blood pressure, at least not directly. However, if you are being treated for hypertension, calcium supplements may indirectly cause your blood pressure to rise by interfering with your medication's effects.

Calcium supplements can interfere with the action of certain high blood pressure medications, making them less effective at controlling blood pressure. In this case, the calcium isn’t actually causing your blood pressure to rise; rather, it is stopping your medications from exerting their blood-pressure-lowering effects. 

These interactions are uncommon, and only affect a small number of high blood pressure medicines. The two blood pressure-lowering medications that are most likely to interact with calcium supplements are thiazide diuretics and calcium channel blockers. Here is how calcium supplements can interfere with those two types of medication.

Thiazide Diuretics

Thiazide diuretics work to lower your blood pressure by helping your kidneys get rid of excess water and sodium (rather than holding on to it). Lowering the volume of fluid in your bloodstream relieves some of the pressure, making it easier for your heart to pump.

If you take calcium supplements while using a thiazide diuretic, the calcium can disrupt the diuretic's action on the kidneys, which in turn makes the drug less effective at lowering your blood pressure.

In some cases, taking calcium with a thiazide diuretic can lead to a condition called milk-alkali syndrome in which the body becomes less acidic and blood calcium levels begin to rise. This can lead to hyperkalemia (abnormally high blood calcium), the condition of which increases the risk of heart attack, acute kidney failure, and seizure.

If taking a thiazide diuretic, you should restrict your calcium intake to less than 1,500 milligrams (mg) per day.

Calcium Channel Blockers

Calcium channel blockers help lower blood pressure this way: they stop calcium from interacting with blood vessels, which lowers the blood vessel’s ability to tighten and ultimately leads to looser vessels and lower blood pressure.

It makes sense, then, that calcium channel blockers can also be affected by calcium supplements. However, there's typically only a risk when you're getting extremely high levels of supplemented calcium (such as being given high doses of calcium through IV in a hospital).

In this case, the interaction is very straightforward: very high levels of blood calcium can “out-compete” the drug’s ability to block the interaction between calcium and your blood vessels. In essence, there is so much calcium that the drug simply cannot block it all. When this happens, it can be quickly reversed by stopping the IV administration of calcium.

There is no evidence that oral calcium supplements can interfere with calcium channel blockers. However, to be safe, check your blood pressure regularly if taking calcium supplements and calcium channel blockers together.

Other Blood Pressure Medications

Calcium supplements do not interfere with other common blood pressure medications like ACE inhibitors, beta-blockers, or other types of diuretics. Still, you should always consult your doctor before beginning supplementation with any vitamin, mineral, or herbal product.

Many supplements are known to interact with prescription drugs, which is why you should always consult your doctor or pharmacist before taking supplements, including vitamins and herbal remedies.

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