The US National Institutes of Health (NIH) fact sheet on magnesium does not name a best time of day. The timing that it is specific about is the gap from certain medicines: at least 2 hours from oral bisphosphonates, and some antibiotics at least 2 hours before or 4 to 6 hours after magnesium. If you take neither, choose a time you can keep to.

This guide is about timing and remembering, not about whether you need magnesium or how much to take. That is a question for your doctor, pharmacist or dietitian.

Medicines to keep apart

Magnesium can reduce how well some medicines are absorbed, so the gap matters more than the clock. The NIH gives these examples:

  • Oral bisphosphonates for osteoporosis, such as alendronate: take magnesium-rich supplements or medicines at least 2 hours before or after.
  • Tetracycline antibiotics, such as doxycycline, and quinolone antibiotics, such as ciprofloxacin: take the antibiotic at least 2 hours before or 4 to 6 hours after magnesium.

These are examples and not a full list. Antacids and laxatives can contain magnesium too. Ask your pharmacist to check everything you take, including any thyroid medicine, and to help you plan the times. A medication list makes that quick.

Medicines that can change your magnesium

Some medicines affect magnesium levels rather than absorption. They do not change when you take a supplement, but your doctor may want to know:

  • Loop and thiazide diuretics can increase the magnesium lost in urine.
  • Potassium-sparing diuretics reduce the magnesium lost in urine.
  • Proton pump inhibitors can cause low magnesium when taken for a long time, typically more than a year.

Do not stop or change a prescribed medicine because of this. Raise it with your doctor.

Morning or night?

We could not find a recommended time of day on the NIH fact sheet, so treat strong claims about one with caution. Think about these instead:

  • The gaps above, if they apply to you. They can settle the question.
  • Your stomach. High doses can cause diarrhoea, nausea and cramping. If your product has directions about food, follow them.
  • Your routine. A time you can keep is better than a perfect time you miss.

Why the form on the label matters

Magnesium comes as oxide, citrate, chloride and other forms. Forms that dissolve well in liquid are more completely absorbed. Small studies found aspartate, citrate, lactate and chloride were absorbed more completely than oxide and sulfate. Carbonate, chloride, gluconate and oxide are the forms most often reported to cause diarrhoea.

The Supplement Facts panel on a US label shows elemental magnesium, the amount of magnesium itself, not the weight of the whole compound. Labels elsewhere can differ, so check that you are comparing the same thing. If in doubt, ask your pharmacist.

Limits

The NIH sets the upper limit for supplemental magnesium at 350 mg a day for adults. The NHS in the UK says 400 mg or less a day from supplements is unlikely to cause harm. Both are about supplements and not food, and your doctor may advise something different for you. Very high doses can be dangerous, and magnesium in laxatives and antacids counts as well.

Make it stick

  • Pick one anchor, such as after dinner, and keep the bottle somewhere sensible for that moment.
  • Set the gap once, with your pharmacist, and turn it into a fixed time rather than working it out each day.
  • Log it, so you know whether you already took it.

In Cadence, you can set a reminder for each medicine and supplement, tie one to a meal, or time a dose from another one, such as 4 hours after your first dose. The timing stays your and your pharmacist's decision: Cadence reminds and records. See also our guide to tracking a supplement stack.

Frequently asked questions

Can I take magnesium at the same time as my other tablets?

It depends on what they are. Some need hours between them, so ask your pharmacist to check your list.

Should I take magnesium with food?

Follow the directions on your product. The NIH fact sheet does not set a rule on food, and it notes that high doses can upset your stomach.

How far apart from antibiotics?

For tetracycline and quinolone antibiotics, the NIH says to take the antibiotic at least 2 hours before or 4 to 6 hours after magnesium. Check with your pharmacist for any other antibiotic.

Is magnesium safe with kidney disease?

Ask your doctor before taking it. The kidneys remove excess magnesium, so kidney problems can change what is safe for you.

Sources

Magnesium fact sheet for health professionals, NIH Office of Dietary Supplements. Vitamins and minerals: others, NHS.

Cadence is a free medication reminder app for iPhone and Apple Watch. It is not medical software and does not give medical advice. Cadence Pro is a one-time purchase, with no subscription.