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.
60 of 938 Reddit owner comments about Magnesium (6%) describe an unwanted effect. The effects people mention most are grogginess, drowsiness or fatigue, vivid dreams or nightmares and stomach upset or digestive changes. These are self-reports from Reddit sleep, insomnia 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: 4.2 · tolerability 4.6 (higher means fewer unwanted-effect reports).
What people describe
| Effect mentioned | Owner comments |
|---|---|
| Grogginess, drowsiness or fatigue | 10 |
| Vivid dreams or nightmares | 6 |
| Stomach upset or digestive changes | 5 |
| Trouble sleeping or feeling wired | 5 |
| Headaches | 3 |
How we counted: among the 60 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: 46 owner comments
- Morning grogginess: 12 owner comments
- Taste & form: 7 owner comments
Safety notes from NIH and published research
- The NIH upper limit for magnesium from supplements is 350 mg a day for adults unless a doctor advises more; higher doses commonly cause diarrhea, and people with kidney disease are at higher risk of magnesium build-up.[NIH Office of Dietary Supplements]
- Magnesium can reduce absorption of some antibiotics and osteoporosis drugs, so doses are usually spaced 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
3/5 Side effects“Not commenting on your sheets but if you use magnesium before bed it will help regulate your body temperature as it supports the function of over 300 biochemical processes in your body.”
4/5 CalmingSide 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…”
4/5 Morning grogginessSide effects“I take 10mg of Davigo and 300mg of magnesium every night and sleep like a baby.”
4/5 Morning grogginessStomach upset“high dosing magnesium bisciglynate helped me with sleep (but when taking 800-1000mg it sometimes induces light diarrhea the next day) but maybe it also works at daytime, I didn't test that out”
2/5 Side effects“Interesting because so many people swear by melatonin and I had brain fog and had a hard time waking up, so I stopped taking it and started taking magnesium and I'm so glad I did!”
1/5 Side effectsTaste & form“I'm here 9 years later because I watched a video on tt where a guy was saying that if you take 2 pills of magnesium before sleep, you'll thank him all your life.”
2/5 Morning grogginessSide effects“I use the kind patches “micro” magnesium for sleep and find they are one of the few sleep aids I've tried that don't leave me with that groggy, hung-over-ish feeling the next day provided I get a decent (for me) nights sleep.”
2/5 Stomach upsetSide effects“I've taken blood tests which is why I take the vitamin C D B K magnesium cocktail, I sleep with a HEPA filter 2 ft from my bed, I rarely get headaches but when I do they are debilitating and if anything I'm hot all the time so much so that…”
Frequently asked
What side effects do people report with Magnesium?
60 of 938 Reddit owner comments about Magnesium (6%) describe an unwanted effect; the ones mentioned most were grogginess, drowsiness or fatigue, vivid dreams or nightmares and stomach upset or digestive changes. 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
- Magnesium (form not stated): full Reddit owner rating
- Magnesium dosage and timing
- Does magnesium help you fall asleep?
- Does magnesium help you stay asleep?
- Does magnesium improve deep sleep?
- Best Magnesium for Falling Asleep
- Best Magnesium for Staying Asleep Through the Night
- Best Magnesium for Deep Sleep and Sleep Quality
- Best Magnesium for Anxiety and Racing Thoughts at Night
Compare side-effect reports: Melatonin vs Magnesium (form not stated) · L-theanine vs Magnesium (form not stated)