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
Magnesium supplements are not known to cause muscle twitches or spasms. Low magnesium can cause them, which is why so many people take it for cramps. But most twitches and cramps have other causes, and magnesium helps less often than its reputation suggests. If yours carried on or got worse after you started it, the likeliest explanations are that magnesium was never the cause, or that a high dose is giving you loose stools and you are losing fluid and other minerals as a result.
What the evidence says about magnesium and cramps
A Cochrane review, updated in 2020, looked at the trials of magnesium for muscle cramps. It concluded that magnesium is unlikely to give a meaningful benefit for cramps in older adults, and that the evidence for pregnancy-related cramps is conflicting.
That fits with what the NHS says about the usual causes. For twitches it lists stress and anxiety, tiredness, caffeine or alcohol, and some medicines. For leg cramps it lists ageing, exercise, pregnancy, dehydration and medicines such as statins and water tablets. Magnesium is not mentioned as a treatment.
A true magnesium deficiency does cause twitching, cramps and tremor. It is uncommon in healthy people and is usually linked to something specific: long-term use of some acid-reflux medicines (PPIs) or water tablets, heavy drinking, or a gut condition that affects absorption. A GP can check for it.
Why twitches might continue or get worse on magnesium
The cause was something else
If stress, poor sleep, caffeine or a medicine is behind your twitches, magnesium won’t change them. As they often come and go on their own, it can look as if the supplement first helped and then stopped working.
Loose stools from too high a dose
This is the main way magnesium can make things worse. Citrate, oxide and chloride draw water into the gut. The NHS says more than 400 mg a day can cause diarrhoea. Ongoing diarrhoea means losing fluid and potassium, and both dehydration and low potassium are recognised causes of cramps and muscle weakness.
Taking more when it doesn’t work
It is tempting to raise the dose when cramps persist. That makes loose stools more likely without making the magnesium more effective.
Other ingredients, and caffeine
Check the label for stimulants in blended products, and take an honest look at your tea, coffee and energy drink intake.
What to try
- Check your dose. Keep supplements to 400 mg a day or less, counting every product you take.
- If you have loose stools, lower the dose, split it across the day, or switch to a form that is gentler on the gut such as glycinate.
- Drink enough, especially in hot weather and around exercise.
- Stretch and massage the affected muscle. This is the first treatment the NHS suggests for cramps.
- Cut back on caffeine and alcohol, and look at your sleep.
- Stop for a couple of weeks and see whether anything changes. If the twitches are the same with or without magnesium, it isn’t the cause or the cure.
An earlier version of this article said magnesium causes cramps by lowering sodium, and advised adding salt. We have removed that advice. There isn’t good evidence for it, and extra salt raises blood pressure. If you think an electrolyte is low, ask your GP for a blood test.
When to see your GP
- A twitch that has lasted more than two weeks, or twitches in more than one place.
- The affected area feels weak or stiff.
- Cramps that disturb your sleep, last longer than 10 minutes, or come with numbness or swelling in your legs.
- You think a prescribed medicine is the cause. Don’t stop it without advice.
- You take a PPI or water tablets long term and have cramps or twitches.
See how magnesium relates to other minerals
Magnesium, potassium, calcium and sodium all play a part in how muscles contract and relax. Tap magnesium on our free Mineral Interaction Wheel to see which nutrients it works with and which it may compete with. For other side effects, read our magnesium side effects guide.
Sources
- Garrison SR, et al. Magnesium for skeletal muscle cramps. Cochrane Database of Systematic Reviews, 2020.
- NHS. Twitching eyes and muscles.
- NHS. Leg cramps.
- NHS. Vitamins and minerals: Others (magnesium).
- NIH Office of Dietary Supplements. Magnesium: Fact Sheet for Health Professionals.