Pharmacists Should Fill Patient Education Gap About Magnesium Supplements and Drug Interactions

Pharmacists Should Fill Patient Education Gap About Magnesium Supplements and Drug Interactions

magnesium supplements and drug interactionsSales of magnesium supplements are booming—they grew by 15 percent in just one year—and the upward trend is expected to continue as studies continue to support the health benefits of the mineral. While this is great for the many people who don’t get enough magnesium in their diet, it’s also a worrisome trend due to the potential for interactions with medications.

This is a classic example of patients who don’t even know they lack critical information because over-the-counter supplements are perceived as harmless. Patients who buy magnesium supplements depend on pharmacists to fill that education gap through counseling about adverse effects that can occur when supplements are mixed with certain drugs.

Prevalence and Health Impact of Magnesium Deficiency

The Estimated Average Requirement (EAR) is the average daily intake needed to sustain the nutritional requirement of half of healthy individuals within a particular group, such as those in a certain life stage or of a specific gender. Based on the EAR, half of Americans—across all groups—fail to consume enough magnesium through their diet.1 When you stop to consider the physiologic roles of magnesium, it’s easy to understand why the Office of Disease Prevention and Health Promotion at the USDA calls it a nutrient of concern.

Magnesium serves as a cofactor for hundreds of enzymes that support energy production, cell signaling, ion transport, cell migration during wound healing, and the synthesis of proteins, RNA, DNA, carbohydrates, lipids and the vital antioxidant glutathione. More specifically, a magnesium deficiency may lead to:

  • Metabolic syndrome: People who consume more than 355 mg of magnesium daily have a 30 percent lower risk of developing metabolic syndrome compared to those who get less than 197 mg/day, reported the British Journal of Nutrition in September 2015.2 It’s important to note that 355 mg/day is only slightly above the recommended dietary allowance of 320 mg/day for women and it’s well below the recommended 420 mg/day for men.
  • Cardiovascular disease: People who don’t get enough magnesium are more likely to have systemic inflammation as measured by levels of C-reactive protein.3 High C-reactive protein is strongly associated with an increased risk of myocardial infarction and stroke.
  • Hypertension: Higher levels of magnesium as determined by urinary excretion, which is a better predictor of deficiency than blood levels, represent a lower risk for developing hypertension.4
  • Low bone mineral density: Magnesium comprises about 1 percent of bone mineral, where it affects the bone matrix and bone mineral metabolism.5 It’s also needed to synthesize vitamin D, which in turn ensures adequate absorption of dietary calcium.
  • Diabetes: Low levels of magnesium are associated with a higher risk of diabetes. Conversely, supplemental magnesium may improve the function of pancreatic beta-cells and increase insulin sensitivity.

Magnesium Supplement Toxicity and Drug Interactions

Many customers buying magnesium supplements aren’t aware of two significant potential risks, so it’s essential to reach out and offer patient education. The first concern is toxicity. Adverse effects aren’t known to occur with magnesium obtained through food, but getting too much through supplemental magnesium can become toxic. At the least, excessive magnesium causes diarrhea. Patients with impaired kidney function must be especially careful. When the kidneys don’t work properly, even a moderate dose from magnesium-containing antacids or laxatives may cause hypotension, lethargy, and cardiac arrhythmia. For this reason, the tolerable upper intake for supplemental magnesium is 350 mg/day for everyone who is 9 years and older. The second major concern is drug interactions. Magnesium can interfere with a number of different drugs such as:

  • Antibiotics: Magnesium can interfere with the absorption of quinolone and tetracycline antibiotics, so supplements should be taken 1 hour before or 2 hours after taking these medications. Magnesium and aminoglycosides may both affect muscles, so their cumulative impact can lead to serious problems.
  • Bisphosphonates: Alendronate, tiludronate, risedronate and other drugs used to treat osteoporosis are less effective when taken with supplements because magnesium blocks their absorption. Bisphosphonates should be taken at least two hours before magnesium.
  • Digoxin: Digoxin causes more magnesium to be eliminated through urine. Additionally, hypomagnesemia lowers the therapeutic efficacy of digoxin and may predispose patients to digitalis toxicity. To make matters worse, low magnesium adds to cardiovascular stress. The bottom line is that magnesium levels must be tightly maintained in patients taking digoxin
  • Gabapentin: Since magnesium can block its absorption, gabapentin should be taken at least 2 hours before or 4 to 6 hours after taking magnesium supplements.6
  • Sulfonylureas: Magnesium salts can increase the amount of sulfonylureas the body absorbs. Patients should consult their physician because the dose of sulfonylurea agents may need to be adjusted to maintain normal blood sugar.
  • Calcium channel blockers: Magnesium from supplements may also block calcium from entering cells, so they can cause low blood pressure when taken with antihypertensives such as nifedipine, verapamil, and amlodipine.
  • Muscle relaxants: Patients should cautiously combine magnesium with muscle relaxants, as the supplements may potentiate the side effects of the relaxants.
  • Diuretics: Thiazide and loop diuretics can deplete magnesium, so doctors may recommend supplemental magnesium in these patients. On the flip side, potassium-sparing diuretics taken together with magnesium may result in excessive magnesium.
  • Anticoagulants: Since magnesium can slow blood clotting, patients should consult their physician before mixing supplements with anticoagulants.

Warnings about over-the-counter products:

Counseling patients who take prescription medications only requires including information about magnesium supplements when you talk with them about adverse effects. Reaching out to those buying over-the-counter products is a bigger challenge, but it’s important to alert them about problems that may occur if they mix aspirin and antacids with supplemental magnesium. One tactic is to give them a generic handout about antacid use that includes all related health concerns. You might also consider putting up a notification near the antacid products suggesting that patients consult the pharmacist before mixing them with supplements.

Educate Patients About Magnesium Supplements

When it comes to nutritional advice, patients are always told that the best way to obtain nutrients is through their diet rather than from supplements. And that’s certainly true. In fact, it’s rare for people who eat a well-balanced, nutrient-rich diet to have a magnesium deficiency. But in the real world, at least half of your patients don’t fit that profile, which means they need assistance with meal planning, supplements, or a combination of both. Pharmacists fill an invaluable service and protect their patients’ long-term health when they include information about magnesium supplements in their routine counseling.

Pharmaceutic North America provides a variety of high-quality pharmaceuticals, including prescription drug products, bulk and unit-dose active pharmaceutical ingredients, and OTC supplements. Contact us today to talk about how we can support your pharmaceutical needs.

Show 6 footnotes

  1. “Percent of Population with Usual Intakes Below EAR,” 2015,
  2. “Dietary Intake of Calcium and Magnesium and the Metabolic Syndrome in the National Health and Nutrition Examination (NHANES) 2001 – 2010 Data,” September 2015,
  3. “Dietary Magnesium Intake is Inversely Associated with Serum C-reactive Protein Levels: Meta-Analysis and Systematic Review,” February 2014,
  4. “Urinary Magnesium Excretion and Risk of Hypertension: The Prevention of Renal and Vascular End-Stage Disease Study,” June 2013,
  5. “Magnesium,” October 2013,
  6. “Magnesium Interactions,” accessed October 2016,

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