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The 4 Best Magnesium Supplements for Pregnancy

Why pregnant people are reaching for magnesium

Three of the most common pregnancy complaints, leg cramps, insomnia, and constipation, all have credible evidence that magnesium helps. A 2017 randomized trial showed a 50% reduction in leg-cramp frequency for the magnesium group (86%) versus placebo (60.5%). Sleep research consistently shows magnesium glycinate improves sleep efficiency.

The catch: form matters. Magnesium oxide is poorly absorbed and tends to cause diarrhea at any meaningful dose. Magnesium glycinate (or bisglycinate) is the form most pregnancy research uses, well-absorbed, gentle on the gut, and the glycine itself supports sleep.

What to look for

• Glycinate / bisglycinate form as the primary or only magnesium.
• Elemental magnesium clearly labeled, not "magnesium glycinate 1,000 mg" (most of that weight is the glycine carrier; the elemental dose is what your body uses).
• Third-party tested for purity (NSF, USP, or brand-published COA).

What to avoid

• Magnesium oxide as the primary form, laxative effect, low absorption.
• Mega-doses above 350 mg supplemental during pregnancy without clinician approval.
• Blends with stimulants ("magnesium + energy"), those don't belong in a pregnancy bottle.

Our top picks

1. Pure Encapsulations Magnesium (Glycinate), Score: 88/100

The clinician-trusted brand. 120 mg elemental magnesium glycinate per capsule, so you can dose to your tolerance (1–3 capsules). Hypoallergenic, NSF-tested, no fillers. Best overall.

2. Thorne Magnesium Bisglycinate, Score: 87/100

Powder format, mix into water in the evening, sip before bed. NSF Certified for Sport (the most stringent supplement certification). 200 mg elemental per scoop, monk-fruit sweetened. Best for an evening sleep ritual.

3. Needed Magnesium, Score: 84/100

A blend of glycinate, malate, and taurate, 300 mg elemental total. Practitioner-recommended for the full benefit profile (sleep, cramps, restless legs). 3 capsules a day. Best if you want multiple magnesium forms in one bottle.

4. Natural Vitality Calm Magnesium Citrate Powder, Score: 67/100 (caution)

The popular drugstore option. Magnesium citrate form, effective for pregnancy constipation but loose stools at full dose. Start with a half scoop. Best for constipation specifically; not the right form if your goal is sleep or cramps.

When to take it

• Cramps/sleep: 30–60 minutes before bed.
• Constipation (citrate form only): morning, with plenty of water.
• Don't combine two magnesium products without adding up the elemental totals, exceeding 350 mg/day from supplements can cause diarrhea and electrolyte issues.

Talk to your OB if…

• You're on blood pressure medication (magnesium can affect BP).
• You have kidney disease (changes magnesium clearance).
• You're approaching preterm labor with concerns about preterm contractions (your OB may already be using IV magnesium clinically).

How we ranked

Same composite scoring rubric used across the site, see methodology.

Medical disclaimer: Not medical advice. Cap total supplemental magnesium at 350 mg/day during pregnancy, and check with your OB before starting any new supplement.