What Not to Take With Magnesium, and What Pairs Well

Most problems with magnesium are about timing, not danger: it binds some medicines in the gut and stops them being absorbed. Take tetracycline and quinolone antibiotics at least 2 hours before or 4 to 6 hours after a magnesium supplement¹, and keep levothyroxine 4 hours away from antacids and calcium or iron supplements².

The real reasons not to take magnesium without a doctor are kidney disease and very high doses, because the kidneys are what clear the excess¹.

Five drug groups lose absorption when they meet magnesium in the gut, so they need spacing rather than avoidance. Magnesium binds these drugs in the gut into complexes that are poorly absorbed¹. Interactions also run the other way, because magnesium and many drugs share transport pathways in the body³.

• Tetracycline and quinolone antibiotics (doxycycline, ciprofloxacin, levofloxacin): magnesium forms insoluble complexes with them, so take the antibiotic at least 2 hours before or 4 to 6 hours after the supplement¹.
• Oral bisphosphonates (alendronate for osteoporosis): keep magnesium at least 2 hours away¹. The alendronate label says antacids and multivalent cations interfere, and asks for at least 30 minutes after the dose before any other oral medicine⁴.
• Levothyroxine: the label says not to take it within 4 hours of iron and calcium supplements or antacids².
• Gabapentin: an aluminum and magnesium hydroxide antacid cut its bioavailability by about 20%, so the label advises taking gabapentin at least 2 hours after the antacid⁵.
• Dolutegravir (an HIV medicine): take it 2 hours before or 6 hours after cation-containing antacids or laxatives⁶.

How much does timing matter?

A lot. In healthy men given 750 mg of ciprofloxacin, a magnesium and aluminum antacid taken 5 to 10 minutes earlier left only 15.1% of the usual absorption⁷. Two hours earlier it was 23.2%, and 4 hours earlier it was 70%⁷. Taking the antacid 6 hours before or 2 hours after the antibiotic had no effect⁷.

Supplements behave more mildly than antacids. In a crossover trial in 15 healthy adults, magnesium aspartate taken with 1 mg of levothyroxine cut its absorption by 12%, while magnesium citrate cut it by a non-significant 7%⁸. The authors still advise people with hypothyroidism to separate the two⁸.

If you take magnesium during a course of antibiotics, our guide to antibiotics and supplements covers probiotics, calcium and zinc too. If you have hypothyroidism or osteoporosis, the spacing rules above apply every day, not just during a course.

Common pain relievers such as ibuprofen are not among the examples on the NIH list of magnesium interactions¹. That list gives examples rather than every drug, so ask a pharmacist about anything you take daily¹.

Some drugs work the other way: they lower or raise your magnesium over months, which matters more than any single dose.

• Loop and thiazide diuretics (furosemide, hydrochlorothiazide): long-term use increases magnesium loss in urine and can deplete it¹.
• Potassium-sparing diuretics (amiloride, spironolactone): these reduce magnesium excretion, so magnesium can build up instead¹.
• Proton pump inhibitors (omeprazole, esomeprazole, lansoprazole): taken for long periods, typically over a year, they can cause low magnesium¹.

With acid reducers, supplements are not always enough. In the cases the FDA reviewed, magnesium supplements failed to raise low levels in 25% of people, who had to stop the drug¹. The FDA advises checking magnesium before long-term use and periodically after¹.

The size of the risk is less clear than the warnings suggest. A 2019 review of 15 observational studies in 129,347 people pooled 14 of them and found a 44% higher risk of low magnesium (RR 1.44)⁹. The link disappeared when outpatients and hospital patients were analysed separately, and the authors called it unclear⁹.

If you take an acid reducer for GERD, ask for a magnesium test rather than guessing. Our page on magnesium for deficiency covers what repletion looks like.

Usually yes. Calcium channel blockers such as amlodipine and diltiazem are not among the examples on the NIH list of magnesium interactions; the diuretics above are¹. Because magnesium lowers blood pressure slightly, tell your prescriber you take it.

The effect is small. A 2016 meta-analysis of 34 double-blind trials in 2,028 adults found that a median 368 mg a day for 3 months lowered systolic pressure by 2.00 mmHg and diastolic by 1.78 mmHg¹⁰. The same analysis found 300 mg a day was enough to raise blood magnesium and lower pressure, and its summary does not compare magnesium forms¹⁰. The effect is too small to replace a prescription; if you take blood pressure medicine, your prescriber can watch for any extra drop.

So high blood pressure is not, by itself, a reason to avoid magnesium. Kidney disease is, and it often travels with high blood pressure. The evidence for blood pressure is on our magnesium for blood pressure page, and drug-by-drug advice is in blood pressure meds and supplements.

The documented clashes are with other minerals, not vitamins: high-dose zinc is the clearest, iron is worth spacing, and calcium at normal doses looks fine^{11, 12, 13}. Vitamin D and B6 are paired with magnesium in trials, covered below^{14, 15}.

• Zinc, at high doses: in a metabolic-ward study, 142 mg a day of zinc sulfate significantly reduced magnesium absorption and balance in adult men¹¹. In 25 postmenopausal women, 53 mg of zinc a day for 90 days also lowered magnesium balance¹⁶. A typical zinc supplement is far below the first dose, but stacked products can creep toward the second.
• Iron: in prenatal multivitamins with 60 to 65 mg of iron, women absorbed only 1.8 to 3.0 mg of iron, against 8.1 mg from iron alone¹². The researchers traced this to calcium carbonate and magnesium oxide in the tablets¹². If you take iron for low stores, take it apart from magnesium; see iron absorption.
• Calcium: in a small crossover study in 5 adolescent girls, raising calcium from 800 to 1,800 mg a day did not change magnesium absorption or balance¹³. Taking calcium with magnesium is reasonable, though the study is too small to rule out a modest effect.

The same metal-binding problem means magnesium, calcium and zinc can all reduce tetracycline absorption³. So a multimineral is the product to space from your antibiotic, not only a magnesium tablet.

Vitamin D and vitamin B6 are the two pairings with trial data^{14, 15}, and different magnesium forms combine safely within one daily limit¹.

• Vitamin D: lab and animal studies suggest the enzymes that make and break down vitamin D depend on magnesium¹⁴. In a randomized trial in 180 adults aged 40 to 85, magnesium raised 25-hydroxyvitamin D when starting levels were near 30 ng/mL, but lowered it when levels started higher¹⁴. Taking the two together is sensible; expecting magnesium to fix low vitamin D is not.
• Vitamin B6: in 264 stressed adults with low blood magnesium, 300 mg of magnesium with 30 mg of B6 cut stress scores by 44.9% in 8 weeks, against 42.4% for magnesium alone, a difference that was not significant¹⁵. Only people with severe stress did better with the pair, by 24%¹⁵. Vitamin B6 adds little for most people.
• Other magnesium forms: glycinate, citrate, oxide and threonate can be taken together. The limit is the total: 350 mg a day of supplemental magnesium for adults, counting every form and any magnesium antacid or laxative¹.

Food magnesium does not count toward that limit, because healthy kidneys clear the excess¹; see magnesium-rich foods. To choose between forms, see magnesium glycinate vs citrate.

Supplements in this guide

• Magnesium
• Zinc
• Iron
• Calcium
• Vitamin D
• Vitamin B6 (Pyridoxine)

People with kidney disease should not take magnesium without their doctor's advice, because failing kidneys cannot remove the excess¹.

Children have much lower limits: 65 mg a day of supplemental magnesium at ages 1 to 3 and 110 mg at ages 4 to 8¹. A 28-month-old boy died of magnesium toxicity after very large doses¹, so keep adult products and magnesium laxatives away from children and ask a pediatrician before giving any.

Too much magnesium shows up first as diarrhea, nausea and cramping¹. Carbonate, chloride, gluconate and oxide are the forms most often reported to cause diarrhea¹. Toxicity is rare and mostly seen with laxatives and antacids giving over 5,000 mg a day¹. Its signs include low blood pressure, vomiting, muscle weakness, difficulty breathing and an irregular heartbeat¹.

Magnesium laxatives carry their own warnings. One magnesium citrate solution label provides 290 mg of magnesium per fluid ounce¹⁷. It says to ask a doctor first if you have¹⁷:

• kidney disease;
• a magnesium-restricted diet;
• abdominal pain, nausea or vomiting;
• a sudden change in bowel habits lasting over 2 weeks.

The same label says to take it 2 or more hours before or after other drugs¹⁷. If you have ulcerative colitis or another bowel condition, the laxative effect is the issue to raise with your doctor. For constipation itself, see magnesium for constipation.

Fix the medicine's time first, then put magnesium in the gap the label allows. One sample day, using the spacing above:

• 7 am: alendronate with plain water, at least 30 minutes before food or any other medicine⁴; or levothyroxine as your prescriber directs.
• Noon: calcium or a multimineral with lunch, if you take one, at least 4 hours after levothyroxine².
• Evening: magnesium, well clear of the morning dose and at least 2 hours from the bisphosphonate¹.
• On an antibiotic: follow the antibiotic spacing above, and move the magnesium if the doses collide.

Because magnesium oxide and calcium carbonate in the same tablet cut iron absorption¹², it is reasonable to take iron at a different time, for example iron in the morning and magnesium at night. Our guide on when to take magnesium covers morning versus night for sleep and cramps.

We searched PubMed for reviews, trials and pharmacokinetic studies on magnesium and drug or mineral interactions, and read the NIH Office of Dietary Supplements fact sheet and five current drug labels on DailyMed. We read 11 journal records and 6 official pages, and cited all of them.

Label directions and pharmacokinetic studies came first, because spacing advice comes from them. Several mineral studies are small or decades old, and few test supplement forms such as glycinate directly. Researched and written in October 2026.

1. National Institutes of Health, Office of Dietary Supplements. Magnesium: Fact Sheet for Health Professionals. https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/
2. DailyMed. Levothyroxine sodium tablets: prescribing information (revised August 2024), section 17 Drug-Food Interactions. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=5100c561-0028-a3c0-e063-6394a90addeb
3. Gröber U. Magnesium and Drugs. Int J Mol Sci. 2019;20(9). doi:10.3390/ijms20092094
4. DailyMed. Alendronate sodium tablets: prescribing information (revised February 2021), section 7.1 Calcium Supplements/Antacids. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c23fb7fe-c6b9-4f77-bde7-992222b589d3
5. DailyMed. Gabapentin capsules: prescribing information, section 7.3 Maalox (aluminum hydroxide, magnesium hydroxide). https://dailymed.nlm.nih.gov/dailymed/lookup.cfm?setid=54dc347e-cba0-ea73-e063-6294a90ab436
6. DailyMed. Dolutegravir tablets: prescribing information, sections 2 and 7 (polyvalent cations). https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=807b0cd2-093c-4353-a4a5-2e1f264616ba
7. Nix DE, et al. Effects of aluminum and magnesium antacids and ranitidine on the absorption of ciprofloxacin. Clin Pharmacol Ther. 1989;46(6):700-5. doi:10.1038/clpt.1989.207
8. Attinger MC, et al. Single Center, Open-Label, Randomized Crossover Trial on Drug-Drug Interactions of Levothyroxine/Magnesium-Citrate and Levothyroxine/Magnesium-Aspartate in Healthy Subjects-The ThyroMag Trial. Clin Transl Sci. 2025;18(11):e70409. doi:10.1111/cts.70409
9. Liao S, et al. Does the use of proton pump inhibitors increase the risk of hypomagnesemia: An updated systematic review and meta-analysis. Medicine (Baltimore). 2019;98(13):e15011. doi:10.1097/MD.0000000000015011 Our study summary.
10. Zhang X, et al. Effects of Magnesium Supplementation on Blood Pressure: A Meta-Analysis of Randomized Double-Blind Placebo-Controlled Trials. Hypertension. 2016;68(2):324-33. doi:10.1161/HYPERTENSIONAHA.116.07664 Our study summary.
11. Spencer H, et al. Inhibitory effects of zinc on magnesium balance and magnesium absorption in man. J Am Coll Nutr. 1994;13(5):479-84. doi:10.1080/07315724.1994.10718438
12. Seligman PA, et al. Measurements of iron absorption from prenatal multivitamin--mineral supplements. Obstet Gynecol. 1983;61(3):356-62. https://pubmed.ncbi.nlm.nih.gov/6823378/
13. Sojka J, et al. Magnesium kinetics in adolescent girls determined using stable isotopes: effects of high and low calcium intake. Am J Physiol. 1997;273(2 Pt 2):R710-5. doi:10.1152/ajpregu.1997.273.2.R710
14. Dai Q, et al. Magnesium status and supplementation influence vitamin D status and metabolism: results from a randomized trial. Am J Clin Nutr. 2018;108(6):1249-1258. doi:10.1093/ajcn/nqy274 Our study summary.
15. Pouteau E, et al. Superiority of magnesium and vitamin B6 over magnesium alone on severe stress in healthy adults with low magnesemia: A randomized, single-blind clinical trial. PLoS One. 2018;13(12):e0208454. doi:10.1371/journal.pone.0208454 Our study summary.
16. Nielsen FH, et al. A moderately high intake compared to a low intake of zinc depresses magnesium balance and alters indices of bone turnover in postmenopausal women. Eur J Clin Nutr. 2004;58(5):703-10. doi:10.1038/sj.ejcn.1601867
17. DailyMed. Magnesium citrate oral solution (saline laxative): drug facts label, Warnings and Directions. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4e6a64a0-e453-709b-e063-6294a90a7443