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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.