This article is for general information only and is not medical advice. If you have a health condition, take prescribed medication or are pregnant, speak to your doctor or pharmacist before changing your supplements.
The short answer
Feeling worse on magnesium is common, and it’s usually fixable. The most frequent causes are taking too much at once, a form that doesn’t suit you, the time of day you take it, or knock-on effects on other minerals, especially if magnesium is causing loose stools.
Magnesium works as part of a team with sodium, potassium, calcium, vitamin D and vitamin B1. Supplementing it on its own, at high doses, can shift that balance. Small changes to dose, form, timing and diet sort most problems out within days to a couple of weeks.
Get urgent medical help if you have chest pain, a racing or irregular heartbeat that doesn’t settle, fainting, or real difficulty breathing. Don’t wait to adjust your supplements.
From me: why I wrote this
Like a lot of people, I started taking magnesium because it’s recommended for almost everything: sleep, stress, cramps. It helped at first. Then I started running into the side effects nobody mentions, and I learned the hard way that more isn’t always better. The time I left a magnesium oil-soaked tissue in my sock overnight, as an experiment, left me with aching bones and an upset stomach the next day.
I started Mineral Balance because the same questions kept coming up from people I spoke to online: why has magnesium stopped working? and why does it make me feel worse? This guide pulls together what I’ve learned, checked against the research, so you can work out what’s going on for you.
Why magnesium doesn’t work alone
Magnesium is involved in hundreds of processes in the body, and many of them depend on other minerals and vitamins at the same time. Change one, and the others can shift. These are the partnerships that matter most when magnesium makes you feel worse:
| Partner | How it’s linked to magnesium | Why it matters here |
|---|---|---|
| Potassium | The body needs enough magnesium to hold on to potassium. Low magnesium is a common cause of low potassium (Huang & Kuo, 2007). | Loose stools from magnesium can also flush potassium out. |
| Calcium | Magnesium helps regulate the hormone that controls calcium. The two also compete for absorption at high doses. | Very high magnesium with little calcium in the diet can upset the balance. |
| Sodium | Sodium keeps fluid in balance. It’s lost through sweat, frequent urination and diarrhoea. | People on low-salt diets who drink a lot of water may notice this most. |
| Vitamin D | The body needs magnesium to convert vitamin D into its active form (Uwitonze & Razzaque, 2018). | High-dose vitamin D can increase your need for magnesium, and vice versa. |
| Vitamin B1 (thiamine) | B1 needs magnesium to work, and the two are closely linked in energy production. | Low B1 is one reason some people don’t tolerate magnesium well. |
The most common way magnesium throws other minerals off is simple: loose stools. Several forms of magnesium draw water into the gut, and when you take more than your body can absorb, you lose sodium and potassium along with the water. That’s why dose and form matter so much.
Common side effects and what’s behind them
Feeling tired, flat or low
This is the complaint we hear most, often from people taking magnesium glycinate. Glycinate is magnesium bound to glycine, an amino acid with a calming effect of its own that has been studied as a sleep aid. For some people the combination is simply too sedating, especially in the morning or at high doses.
Other causes include taking more than you need, and losing sodium or potassium through loose stools. If low mood lasts more than a couple of weeks, see your GP: it deserves a proper look whatever the cause. You can read more in magnesium is making me feel depressed.
Anxiety, restlessness or feeling wired
Some people feel more anxious or “buzzy” on magnesium, or calm at night but on edge the next day. Possible reasons include the form (malate and threonate are more energising for some), a dose that’s too high, or other supplements in your routine. Try one change at a time so you can tell what helped. More in magnesium causing me anxiety.
Worse sleep
Magnesium improves sleep for many people, but not all. Some sleep more lightly, wake in the night, or feel groggy the next day. Try taking it earlier in the evening rather than at bedtime, lowering the dose, or switching form. Some people report sleep problems for a while after stopping magnesium too, so reduce the dose gradually rather than stopping suddenly.
Bloating, loose stools, reflux or water retention
Digestive side effects are the best-established ones. Citrate, oxide and chloride draw water into the gut, which can cause bloating, wind and diarrhoea. Loose stools are the clearest sign you’re taking more than your body can absorb.
Some forms, such as oxide and hydroxide, neutralise stomach acid, which is why they’re used in antacids. If magnesium seems to upset your digestion or cause reflux, try a gentler form like glycinate, split the dose, or take it with food. Changes in fluid balance can also cause temporary water retention for some people.
Palpitations or chest symptoms
Magnesium is involved in heart rhythm, and some people notice palpitations or a tight chest after starting it. Don’t try to fix these yourself. Stop taking magnesium and speak to your GP. If you have chest pain, a heartbeat that won’t settle, fainting or difficulty breathing, call 999 or go to A&E. If you already have a heart rhythm condition such as atrial fibrillation, only take magnesium under your doctor’s guidance.
“My blood test says my magnesium is normal”
A normal result doesn’t always mean your magnesium stores are fine. Less than 1% of the body’s magnesium is in the blood; most is in bone and inside cells. The NIH notes that blood levels have little link with how much magnesium the body holds overall. The body works hard to keep blood levels steady, so a standard serum test can look normal even when stores are low.
- Magnesium: ask your GP whether a red blood cell (RBC) magnesium test is appropriate. It isn’t perfect, but it gives more information than serum alone.
- Potassium, sodium and calcium: standard blood tests for these are reliable and worth having, especially if you have symptoms.
- Keep a symptom diary: note what you take, when, and how you feel. Patterns over a week or two are more useful than a single day.
What to try
Make one change at a time and give it a few days, so you know what made the difference.
- Lower the dose. The NHS says adults need about 270 mg (women) to 300 mg (men) of magnesium a day, and that taking more than 400 mg a day can cause diarrhoea. Many people do well on far less, especially if their diet includes nuts, seeds, leafy greens and whole grains. Start low and build up slowly.
- Split it up. Two smaller doses with meals are often better tolerated than one large one.
- Change the timing. If it makes you drowsy or groggy, take it earlier in the evening. If it disturbs your sleep, try taking it in the day.
- Switch form. Different forms suit different people (see the table below).
- Check your diet for partner minerals. Food is the safest way to top up: potatoes, beans, bananas and dried apricots for potassium; dairy, fortified plant milks, tinned fish with bones and tofu for calcium; and don’t cut salt out entirely if you drink a lot of water or sweat heavily.
- Look at your other supplements. High-dose vitamin D, zinc or calcium taken alongside magnesium can change how you feel. Check your B1 intake too: wholegrains, pork, legumes and seeds are good sources.
- Check medicines. Magnesium can interfere with some antibiotics, osteoporosis medicines and thyroid tablets, so take it at a different time of day. Long-term use of some acid-reflux medicines (PPIs) and water tablets (diuretics) can lower magnesium. Ask your pharmacist.
Magnesium forms at a glance
| Form | Often chosen for | Watch out for |
|---|---|---|
| Glycinate / bisglycinate | Calm, sleep, gentle on the stomach | Can be too sedating for some; next-day grogginess |
| Citrate | Well absorbed, constipation | Loose stools and bloating at higher doses |
| Malate | Energy, muscle aches | Can feel stimulating; some report reflux |
| Taurate | Calm; often used for heart health | Less studied |
| L-threonate | Focus and memory | Expensive; low magnesium per capsule; some find it stimulating |
| Chloride (incl. sprays) | Topical use, muscle soreness | Easy to overdo on the skin; can loosen stools taken by mouth |
| Oxide | Cheap; used for constipation and indigestion | Poorly absorbed; strong laxative effect |
Our vitamins and minerals interactions chart and our free Mineral Interaction Wheel show how magnesium relates to other minerals at a glance, and the guide to mineral balancing goes into more detail.
Speak to a doctor before taking magnesium if you
- have kidney disease or reduced kidney function, because the kidneys clear excess magnesium
- have a heart condition, including an irregular heartbeat, or take heart or blood pressure medicines
- are thinking of taking potassium supplements, which can be dangerous for people with kidney problems or on some blood pressure medicines
- are pregnant or breastfeeding
- take any regular prescribed medicine
Don’t stop or change a prescribed medicine because of anything you read here. Speak to your doctor or pharmacist first.
Questions we often get asked
I’ve taken magnesium for years without problems. Why does it suddenly make me tired?
Something else has usually changed: your diet, stress, a new medicine or supplement, an illness, or how much you’re sweating or drinking. Look at what’s different in the last few weeks, and speak to your GP if it doesn’t settle.
Magnesium calms me at night, but I feel anxious the next day. Why?
It may be the dose or the form. Try a lower dose, taking it earlier in the evening, or a different form, one change at a time.
Should I take calcium with magnesium?
Most people get enough calcium from food. If you take both as supplements, take them at different times of day, as they compete for absorption at high doses.
Is magnesium spray safer than tablets?
Not necessarily. How much gets through the skin is uncertain, and it’s easy to use a lot without realising. Start with a small amount.
How long until I feel better after a change?
Digestive side effects often settle within a day or two of lowering the dose. Other changes can take one to two weeks to judge.
Sources
- NHS. Vitamins and minerals: Others (magnesium).
- NIH Office of Dietary Supplements. Magnesium: Fact Sheet for Health Professionals.
- Huang CL, Kuo E. Mechanism of hypokalemia in magnesium deficiency. Journal of the American Society of Nephrology, 2007.
- Uwitonze AM, Razzaque MS. Role of magnesium in vitamin D activation and function. Journal of the American Osteopathic Association, 2018.
- Yamadera W, et al. Glycine ingestion improves subjective sleep quality in human volunteers. Sleep and Biological Rhythms, 2007.