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Magnesium · side effects reported by users

Magnesium Side Effects: What Reddit Users Report

About this entry (Magnesium (form not stated)): Comments that name magnesium without a form (or a multi-form blend). Counted separately from glycinate/threonate/taurate.

35 of 438 Reddit owner comments about Magnesium (8%) describe an unwanted effect. The effects people mention most are racing heart or palpitations and headaches. These are self-reports from Reddit anxiety, stress and supplement communities (May 2026 to October 2026), not a measured side-effect rate, and many people report no problems at all.

Magnesium (form not stated) overall: 4.1 · tolerability 4.5 (higher means fewer unwanted-effect reports).

What people describe

Effect mentioned	Owner comments
Racing heart or palpitations	5
Headaches	4

How we counted: among the 35 comments that describe an unwanted effect, a category counts when a sentence names the effect with wording like "gave me" or "made me". Questions and sentences about an effect going away are skipped. One comment can count in more than one row, and keyword counts can include some unrelated mentions, so read the quotes below for context.

Most common complaints

Side effects: 29 owner comments
Feeling flat or numb: 5 owner comments
Mood: 5 owner comments

Safety notes from NIH and published research

The NIH upper limit for magnesium from supplements is 350 mg a day for adults; higher doses commonly cause diarrhea, nausea and abdominal cramping.^{[NIH Office of Dietary Supplements]}
Magnesium can reduce the absorption of some antibiotics (tetracyclines, quinolones) and bisphosphonates, so the NIH advises spacing the doses apart.^{[NIH Office of Dietary Supplements]}

Stop and talk to a doctor if an effect is severe or does not settle. Ask a pharmacist about interactions with any medicine you take.

In their words

4/5 Calming effectSide effects
“All minerals compete for the same absorption mechanism so if you're overloading on magnesium then zinc, copper and/or calcium might be out of whack.”

owner comment via r/Supplements · 2026-09-08 · 6 upvotes

4/5 Calming effectSide effects
“I used to have severe health anxiety and deal with stress daily, tried alot of stuff, Taurine in the morning and magnesium before bed helped mostly, I noticed less brain fog and more calm and focus during the day, idk is it directly…”

owner comment via r/Supplements · 2026-07-13 · 9 upvotes

4/5 Side effects
“i felt crazy because everyone said magnesium helps anxiety, but i was laying awake having heart palpitations and anxiety whenever i took it.”

owner comment via r/Supplements · 2026-09-10 · 8 upvotes

2/5 Feeling flat or numbMood
“I get anhedonia when I'm taking too much magnesium.”

owner comment via r/Nootropics · 2026-09-13 · 7 upvotes

4/5 Side effects
“Only thing that's vaguely helped is I have an alarm that goes off at 8:30 pm every night reminding me to take my magnesium and turn the big lights off to put the red one on.”

owner comment via r/sleep · 2026-08-13 · 5 upvotes

2/5 Stomach upsetSide effects
“It was only when I did that dumb shit with the magnesium that I started to feel nauseous and get a headache.”

owner comment via r/Anxiety · 2026-07-02 · 3 upvotes

2/5 Side effects
“For example with a symptom cluster that includes constipation, stiff muscles, poor sleep, and some anxiety I'll suspect low magnesium, especially in a person eating a processed foods diet typically containing inadequate Mg.”

owner comment via r/Supplements · 2026-08-07 · 3 upvotes

2/5 Side effects
“The magnesium supplement often leave me with bad headaches too, I even had to check my self into a mental hospital a couple weeks back because how out of touch I am becoming so now they have to come see me every couple of days to check on me”

owner comment via r/insomnia · 2026-06-29 · 3 upvotes

Frequently asked

What side effects do people report with Magnesium?

35 of 438 Reddit owner comments about Magnesium (8%) describe an unwanted effect; the ones mentioned most were racing heart or palpitations and headaches. These are self-reports, not a measured side-effect rate.

Is Magnesium safe?

Safety depends on your health and medicines. The NIH and other sources listed on this page note specific cautions. Ask a doctor or pharmacist before starting, especially if you take other medicines or are pregnant.

More on Magnesium

Compare side-effect reports: Magnesium glycinate vs Magnesium (form not stated) · L-theanine vs Magnesium (form not stated)