Does magnesium help leg cramps?
Probably not, if your night cramps have no clear cause. In trials in older adults, it meant 0.18 fewer cramps a week than a dummy pill. The NHS suggests something free that takes 5 minutes.
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Does magnesium help leg cramps?
Probably not, if your cramps come at night with no clear cause. A 2020 Cochrane review, which pools all the trials it can find, looked at 11 trials. In the 5 trials of night cramps with no clear cause, mostly in older adults, magnesium made no meaningful difference.
After 4 weeks, people on magnesium had 0.18 fewer cramps a week than people on a dummy pill. That’s about 1 fewer cramp every 5 to 6 weeks.
The true figure could be zero, or even slightly worse. The share of people whose cramps fell by a quarter or more was about the same on magnesium and the dummy pill.
| Who had cramps | What magnesium did | How sure the review is |
|---|---|---|
| Older adults, night cramps with no clear cause | No meaningful change in how often cramps came. | Moderate to high |
| Pregnant women | Mixed. Some trials found a benefit, others did not. | Low |
| People who cramp during exercise | Never tested in a trial. | No evidence |
| People with liver scarring (cirrhosis) | One small trial found no difference. | Low |
Sources: Cochrane 2020: magnesium for cramps; Cochrane 2020: cramps in pregnancy
NICE’s guidance for GPs agrees. It says the review found no benefit to magnesium.
Your next step: try the free NHS calf stretch further down.
What about cramps in pregnancy or after exercise?
In pregnancy, nobody knows yet. A Cochrane review of 8 small studies in 576 women found it unclear whether any treatment works.
Some magnesium trials found fewer cramps, but others found little or no difference. Pregnant? Ask your midwife or GP before you try it.
For exercise cramps, there’s nothing to go on. The review found no trials of magnesium for exercise cramps. So any claim that it stops gym or running cramps is untested.
The NHS says straining your muscles can cause cramps, which can be worse in hot or humid weather. It also lists not drinking enough. Keep your fluids up, and see electrolyte drinks if you sweat a lot.
Which magnesium is best for leg cramps?
None has been shown to work. The night cramp trials used citrate, lactate and oxide by mouth, and one gave magnesium through a drip. Taken together, they made no meaningful difference.
So ignore “best for cramps” labels. UK rules let labels say magnesium contributes to normal muscle function. That’s about normal muscles, not cramps.
Want to try it anyway? The NHS says 400mg a day or less from supplements is unlikely to cause any harm.
- 400 mg a day or belowNHS: unlikely to cause harm.
- Above 400 mg a dayMore than 400mg for a short time: can cause diarrhoea.
Source: NHS
In the cramp trials, gut upset such as diarrhoea hit 11% to 37% of people on magnesium, against 10% to 14% on the dummy pill.
Magnesium can interact with some medicines, such as some antibiotics and bisphosphonates for bones. Tell your pharmacist what you take. For forms and doses, see which magnesium to take and too much magnesium.
What does help leg cramps?
The free 5-minute thing from the top of the page is a wall calf stretch. The NHS says regular calf stretches may help to reduce cramps, but may not stop them completely.
The NHS calf stretch, 3 times a day
- 1
Face a wall
Stand with your arms out, hands just touching it, feet flat.
- 2
Lean in
Press on the wall until your calves stretch. Hold 2 or 3 seconds.
- 3
Stand up straight
Repeat a few times, for 5 minutes.
- 4
Last one before bed
Fewer cramps? Once or twice a day may be enough.
Source: NHS
NICE’s GP guidance says there’s no definite evidence that stretching cuts how often cramps come. But it costs nothing to try.
What to do during a cramp, and at night
- Stretch and massage the muscle.
- Stand up and put your weight on the leg with the cramp.
- For a calf cramp, straighten your leg and pull your toes up towards you.
- Sore afterwards? Paracetamol or ibuprofen can ease it. They won’t help during a cramp.
- In bed on your back, prop your feet on a pillow so your toes don’t point down.
- Keep blankets loose and skip heavy covers.
If stretching hasn’t helped, a GP may offer quinine tablets, a prescription medicine. The NHS says it’s not suitable for everyone.
Could my cramps be a sign of low magnesium?
Possibly, but the NHS doesn’t list it as a cause. The NHS lists ageing, exercise strain, pregnancy, some medicines, not drinking enough and liver disease from drinking too much alcohol. It says the reason for some cramps is unknown.
The US National Institutes of Health lists muscle cramps as a sign of extreme magnesium deficiency. Numbness, tingling and an abnormal heart rhythm are on the same list.
On a statin (a cholesterol medicine) or water tablets (diuretics)? The NHS lists both as possible causes of cramps. Never stop or change a prescribed medicine without your prescriber.
Want to know what a test can show? See blood tests for muscle cramps and signs of low magnesium.
When to speak to a GP
Leg cramps are common and usually harmless. Book a GP appointment if:
- Leg cramps are disturbing your sleep.
- You also have numbness or swelling in your legs.
- A cramp lasts longer than 10 minutes.
- Your cramps change in how often they come, how bad they are or how they feel. NICE’s GP guidance says to go back if so.
Get urgent medical help if severe cramps come with confusion or drowsiness, no pee, or a very high or low temperature. NICE says this needs hospital care.
A GP will examine you to try to find the reason, then suggest a treatment that fits the cause. Cramps on a statin? See statins and muscle aches.