Metoprolol is a medication that widens blood vessels and slows the heart rate. A type of beta blocker, it's useful for lowering high blood pressure and for treating certain other cardiovascular conditions. This medication has a minor interaction with magnesium oxide, but you still should be able to take both these substances. Consult your doctor about using magnesium oxide when you're taking metoprolol.
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While magnesium is a mineral essential for health that is available in food and supplements, magnesium oxide products are generally used for specific gastrointestinal effects. Magnesium oxide is an effective antacid, and in higher doses, it works as a rapid-action laxative. This type of laxative is useful before surgery or a procedure such as a colonoscopy. You can buy magnesium oxide over the counter, but metoprolol is only available by prescription.
Magnesium antacids such as magnesium oxide may decrease the effectiveness of certain beta-blockers if you take them at the same time. However, research is inconclusive, because some studies indicate this is the case while others do not, according to Drugs.com. The way the possible interaction occurs is unclear, but it might be due to a decreased rate of dissolution of the beta blocker in the stomach because of decreased stomach acid.
You should be able to prevent magnesium oxide from reducing your metoprolol medication effectiveness by taking the two substances at least two hours apart, advises Drugs.com. In a small study cited by the website, taking an antacid with a beta blocker reduced peak plasma concentration of the prescription medication. However, taking the antacid two hours after the beta blocker had no effect on the blood-pressure medication.
Metoprolol may have a similar interaction with other products containing magnesium, such as antacids with magnesium carbonate or magnesium hydroxide, or supplements with magnesium. Antacids containing aluminum or calcium, as well as calcium supplements, also may interfere with metoprolol effectiveness if taken at the same time. Your doctor or pharmacist can provide a full list of substances that interact with metoprolol.