In 5 trials with 307 mostly older adults with ordinary night leg cramps, people on magnesium had 0.18 fewer cramps a week than people on placebo after 4 weeks, a gap whose 95% range ran from 0.84 fewer to 0.49 more. The 2020 Cochrane review that pooled them concluded that magnesium is unlikely to make a clinically meaningful difference to cramps in older adults.
What the review measured
The 2020 Cochrane review pooled 11 randomized trials with 735 people, and its abstract does not say which magnesium salts or doses they used. All trials gave magnesium by mouth except one, which used slow infusions into a vein.
A 2020 review of 11 trials in 735 people measured cramp frequency, intensity and duration after magnesium against placebo, nothing, or other cramp therapies: for ordinary cramps in older adults, no measure differed from placebo at 4 weeks. Trials in pregnancy conflicted, and the reviewers rated all 5 of them at high risk of bias.
| Group | Trials and people | Measured | Result | Certainty or limitation |
|---|---|---|---|---|
| Ordinary night cramps, mean age 61.6–69.3 | 5 studies, 307 participants | Cramps a week at 4 weeks | −0.18 a week (95% CI −0.84 to 0.49) | Moderate certainty |
| Same group | 3 studies, 177 participants | Change in weekly cramps | −9.59% (95% CI −23.14% to 3.97%) | Moderate certainty |
| Same group | 3 studies, 177 participants | People with 25% fewer cramps or better | Risk ratio 1.04 (0.84 to 1.29) | High certainty |
| Same group | 2 studies, 91 participants | Cramps rated moderate or severe | Risk ratio 1.33 (0.81 to 2.21) | Moderate certainty |
| Pregnancy | 5 trials, 408 participants | Frequency and intensity | Of 3 placebo trials, 1 positive, 1 null, 1 inconsistent | All 5 at high risk of bias; not pooled |
| Liver cirrhosis | 1 trial, 29 people | Frequency and intensity | No difference | Small; only some had cramps |
| Exercise cramps; motor neuron disease | No trials found | Not measured | Not tested | Evidence gap |
Year · journal · PMID: 2020 · Cochrane Database Syst Rev · 32956536. One review author wrote one of the included trials. Even the point estimate, 0.18 fewer cramps a week, comes to about 1 cramp fewer every 5–6 weeks. The review updates a 2012 version; its searches ran on 9 September 2019, and the authors obtained participant-level data for 4 trials, 1 of them unpublished.
The arithmetic of a dose
The review gives no salt or dose in its abstract, so no form can claim the trials' results. What a dose weighs can still be computed: 200 mg of magnesium as glycinate needs 1,418–1,691 mg of the salt, 2–3 size 00 capsules.
| 200 mg of magnesium as | Salt needed | Size 00 capsules (730 mg each) |
|---|---|---|
| Glycinate (11.8–14.1% magnesium) | 1,418–1,691 mg | 2–3 |
| Citrate (11.3–16.2%) | 1,238–1,770 mg | 2–3 |
| Oxide (60.3%) | 332 mg | 1 |
Ranges come from bound water, which labels rarely state. Bisglycinate also brings about 1.2 g of glycine with each 200 mg of magnesium; the review's abstract does not mention glycine. Capsule counts assume pure salt at 0.8 g/mL with no filler.
On the shelf, 16 of 716 on-market NIH DSLD magnesium labels mention cramps in their label statements (snapshot 2026-08-10); the review above is the test of that wording for older adults.
Which labels to look at
People searching for magnesium glycinate for leg cramps usually compare forms, and the review's abstract names none. This site ranks no label for cramps, because none of the 11 trials gives a cramp result for a named salt to rank by. If you take magnesium for another reason, the rankings compare price per 100 mg within one salt: the cheapest ranked glycinate is Amazon Elements Chelated Magnesium 270 mg at $0.0666 (prices observed 2026-10-26 to 2026-11-02). See the glycinate, citrate and oxide rankings.
Safety
The upper limit for magnesium from supplements is 350 mg a day for adults, set in 1997 and listed by the NIH Office of Dietary Supplements. In the review, minor side effects were more common on magnesium (risk ratio 1.51, 95% CI 0.98 to 2.33; 4 studies, 254 participants; low certainty), mostly gut effects such as diarrhoea in 11–37% of people, against 10–14% on control. Major adverse events were 2 of 72 on magnesium and 3 of 68 on placebo. Talk to a clinician if cramps are frequent, come with swelling, weakness or numbness, began with a new medicine, or happen during pregnancy.