Magnesium L-threonate Side Effects: What Reddit Users Report
About this entry (Magnesium L-threonate (Magtein)): Magnesium bound to L-threonic acid, sold under the Magtein ingredient name.
14 of 104 Reddit owner comments about Magnesium L-threonate (13%) describe an unwanted effect. The effects people mention most are headaches and trouble sleeping or feeling wired. 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 L-threonate (Magtein) overall: 3.4 · tolerability 4.0 (higher means fewer unwanted-effect reports).
What people describe
| Effect mentioned | Owner comments |
|---|---|
| Headaches | 3 |
| Trouble sleeping or feeling wired | 3 |
How we counted: among the 14 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: 12 owner comments
- Morning grogginess: 2 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
4/5 Side effectsVivid dreams“Magnesium L-threonate gave me really good sleep.”
2/5 Emotional bluntingMood“I take 2400 mg fish oil for depression and panic attacks (been taking for 15 years), magtein before bed for anhedonia and sleep (been taking for 6 years), koji fermented iron (magceutics brand, been taking for 6 months) in the morning for…”
2/5 Fast-actingSide effects“Magnesium Threonate worked almost instantly for me, it took away the headache and overall bad feeling I get when sleep deprived.”
4/5 Side effects“I use magnesium glycinate & malate at night and magnesium L-threonate during the day as it helps with memory and brain fog.”
4/5 Side effectsVivid dreams“I like magnesium threonate. Gives me very vivid dreams but never nightmares and it's really improved my sleep.”
1/5 Morning grogginessSide effects“FWIW I've taken Now magtein for 10 years and almost every time I've tried another brand I've had horrible racing heartbeat the next day.”
1/5 Side effects“Magnesium l-threonate and magnesium taurate I tolerate just fine, but magnesium bisglycinate gave me the WORST headache for some reason, and mag malate gave my insomnia (though I'm still experimenting w how I can use the mag malate to my…”
2/5 Side effects“had no idea about the paradoxical thing with glycine until i tried it and spent three nights wired at 3am wondering what was wrong with me switched to magnesium threonate for a bit and it was fine came back to glycinate months later and it…”
Frequently asked
What side effects do people report with Magnesium L-threonate?
14 of 104 Reddit owner comments about Magnesium L-threonate (13%) describe an unwanted effect; the ones mentioned most were headaches and trouble sleeping or feeling wired. These are self-reports, not a measured side-effect rate.
Is Magnesium L-threonate 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 L-threonate
Compare side-effect reports: Magnesium glycinate vs Magnesium L-threonate (Magtein)