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What is the best supplement for muscle cramps in the UK?
No supplement is proven to stop muscle cramps. For cramps in training, sodium and fluid come first; magnesium glycinate at 300mg elemental a day is worth taking where intake is low, common in heavy sweaters. Everything else has weaker evidence.
- Noneproven in trials to stop cramps
- Sodiumfirst for cramps in long, hot sessions
- 300mgelemental magnesium a day where intake is low
- 22pa day for the worked example
Worked example: Futuro Labs Magnesium Glycinate on Amazon UK, 300mg elemental per 2 capsules, £19.99 for 90 days. Label breakdown.
Why the evidence is thin for everything
Cramps are hard to study because they arrive without warning and leave before a lab can measure them. Schwellnus's 2009 review argued that exercise-associated cramps are mostly a fatigue problem, altered nerve control in a muscle worked hard, rather than an electrolyte problem, and Maughan and Shirreffs' 2019 review accepts that while noting that sodium and fluid losses still matter for some people in long hot sessions. Garrison's 2020 Cochrane review of magnesium found it unlikely to help idiopathic cramps and had no usable trials in exercise cramps. So every supplement on this list is sold on mechanism rather than proof.
| Supplement | The claim | What trials show | Verdict |
|---|---|---|---|
| Sodium (salt, electrolyte drinks) | Replaces sweat losses | Sodium loss is linked to cramping in heavy sweaters in long sessions; no trial proves prevention | First thing to fix for training cramps |
| Magnesium (glycinate or citrate) | Normal muscle function, electrolyte balance | Unlikely to help idiopathic cramps (Cochrane 2020); helps where intake is low | Worth taking at 300mg elemental if diet is short; cheap |
| Pickle juice | Stops a cramp in progress | One trial: cramps stopped about 37 seconds faster than water, by a reflex, not by electrolytes | A curiosity for a cramp already happening |
| Potassium | Electrolyte balance | No trial evidence for cramp prevention | Eat fruit and vegetables; do not supplement blindly |
| Vitamin B complex | Nocturnal cramps | One small 1998 trial in older adults reported fewer cramps | Weak; no training data |
| Calcium | Muscle contraction | No trial evidence | Only if intake is genuinely low |
| Magnesium sprays and bath flakes | Absorbed through the skin | No reliable evidence of meaningful skin absorption | Not a supplement |
The one supplement worth buying, and why
Magnesium earns its place on price and probability. Lifters lose magnesium in sweat and urine, Nielsen and Lukaski's review puts athletes at higher risk of marginal intake, and the UK reference intake of 300mg for men is not hard to miss on a diet built around meat, rice and protein powder. Correcting that is cheap: Futuro Labs Magnesium Glycinate gives 300mg elemental magnesium from 1500mg bisglycinate in 2 capsules, 80% NRV, for 22p a day from a 180 capsule bottle at £19.99. Vegan, UK made under GMP and BRC, independently tested for heavy metals and microbiology. If your cramps were an intake problem, a month of that will tell you; if they were a fatigue problem, no supplement was going to fix them and you saved the money on the rest of the list.
| Likely driver | Clue | What to do |
|---|---|---|
| Muscle fatigue and altered nerve firing | Cramps in the muscle you just worked hard, late in a session | Manage volume and pacing; this is the mechanism most sports scientists now put first |
| Sodium loss | Salty sweat marks on kit, cramps in long hot sessions | Salt your food; an electrolyte drink in sessions over an hour |
| Dehydration | Dark urine, headache after training | Drink to thirst plus a little extra on training days |
| Low magnesium intake | Few green vegetables, nuts, seeds or wholegrains; heavy sweating | 300mg elemental a day from a well absorbed form, with food |
| Low potassium or calcium | Very low fruit, vegetable and dairy intake | Fix the diet first; do not supplement calcium without reason |
What to check on the label
- Elemental magnesium of about 300mg per serving, from glycinate or citrate.
- Electrolyte drinks: sodium per litre printed, at least 500mg for long hot sessions.
- No cure claims. Nothing is authorised to prevent or treat cramps.
- Cost per day: magnesium should be about 22p; electrolyte tablets and sprays cost more and do less.
- Batch testing shown for anything you take daily.
The worked example: Futuro Labs Magnesium Glycinate
Futuro Labs Magnesium Glycinate is the worked example on this page because it is the one supplement on the list that is cheap enough to test and honest enough to quote: 300mg elemental per 2 capsules, 80% NRV, low laxative effect, vegan, UK made, lab tested, 22p a day from a £19.99 bottle of 180.
- Elemental magnesium per serving
- 300mg (80% NRV)
- Form
- magnesium bisglycinate 20%
- Serving
- 2 capsules a day
- Bottle
- 180 capsules, 90 days
- Price
- £19.99 (22p a day)
- Capsule
- vegetarian shell, vegan product
Questions people also ask
What supplement stops muscle cramps fast?
Nothing taken by mouth stops a cramp faster than stretching the muscle. Pickle juice shortened electrically induced cramps by about 37 seconds in one trial, through a reflex in the throat rather than electrolytes.
Is magnesium or potassium better for cramps?
Magnesium has trials, even if they are mostly negative; potassium has none for cramp prevention. Take magnesium if intake is low and eat potassium.
Do electrolyte tablets stop cramps in the gym?
They replace sodium and fluid, which matters in long, hot sessions. For a 60 minute lifting session in a cool gym they add little.
What is the best magnesium supplement for cramps in the UK?
A glycinate giving 300mg elemental per serving. Futuro Labs Magnesium Glycinate: 300mg elemental, 22p a day, UK made and lab tested.
Should I see a GP about muscle cramps?
Yes if cramps are frequent, severe, not linked to training, or come with weakness, swelling or numbness. Supplements are for a marginal diet, not a diagnosis.
Sources
- Futuro Labs Magnesium Glycinate listing, Amazon UK, label and price checked 31 August 2026. https://www.amazon.co.uk/dp/B0BT7Z5VQW
- Garrison SR, Korownyk CS, Kolber MR, et al. Magnesium for skeletal muscle cramps. Cochrane Database of Systematic Reviews 2020, Issue 9, CD009402. PubMed record
- Schwellnus MP. Cause of exercise associated muscle cramps (EAMC): altered neuromuscular control, dehydration or electrolyte depletion? British Journal of Sports Medicine 2009;43(6):401-408. https://pubmed.ncbi.nlm.nih.gov/18981039/
- Maughan RJ, Shirreffs SM. Muscle cramping during exercise: causes, solutions, and questions remaining. Sports Medicine 2019;49(Suppl 2):115-124. PubMed record
- Miller KC, et al. Reflex inhibition of electrically induced muscle cramps in hypohydrated humans. Medicine and Science in Sports and Exercise 2010;42(5):953-961. PubMed record
- Chan P, et al. Randomized, double-blind, placebo-controlled study of the safety and efficacy of vitamin B complex in the treatment of nocturnal leg cramps in elderly patients. Journal of Clinical Pharmacology 1998;38(12):1151-1154. PubMed record
- Gröber U, Werner T, Vormann J, Kisters K. Myth or reality, transdermal magnesium? Nutrients 2017;9(8):813. https://pubmed.ncbi.nlm.nih.gov/28788060/
- Nielsen FH, Lukaski HC. Update on the relationship between magnesium and exercise. Magnesium Research 2006;19(3):180-189. PubMed record
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific Opinion on the substantiation of health claims related to magnesium. EFSA Journal 2010;8(10):1807. https://efsa.onlinelibrary.wiley.com/doi/10.2903/j.efsa.2010.1807