Objectives: To find the best evidence of efficiency and safety of magnesium supplementation in correlation with treating muscular cramps. Material and methods: At first it was found Cochrane systematic review on the Cochrane library web page. Other databases were researched: DARE, CENTRAL and MEDLINE to found new systematic reviews and randomised controlled trials (RCTs). After selection systematic review that has the same inclusion and exclusion criteria as Cochrane systematic review, it was conducted quality assessment of systematic reviews using R-AMSTAR checklist. Results: In Cochrane systematic review are included four studies (N=322) that researched magnesium efficiency with idiopathic cramps, and three studies (N=202) were monitoring effectiveness of the magnesium with cramps related with pregnancy. Effect of the magnesium versus placebo on idiopathic cramps, was not statistically significant. The primary endpoint includes, percentage change in the number of cramps per week at four weeks (- 3.93%, 95% CI -21.12 to 13.26, moderate quality evidence) and the difference in the number of cramps per week at four weeks (0.01 cramps/week, 95% CI -0.52 to 0.55, moderate quality evidence). Percentage change in the number of cramps and the difference in the number of cramps per week at four weeks, were small, not statistically significant. Effect of the magnesium on idiopathic muscle cramps in pregnancy-associated cramps is vague, and contradictory. Consistency of side effects of oral magnesium were low and minimally different then placebo (with the possible exception of diarrhoea). Intravenous application of magnesium cause burning sensation at the IV site in half of patients and a small number of patients had asymptomatic hypotension or dizziness. Other systematic review is researching pregnancy-associated cramps and appropriate therapy. It was conducted six randomised controlled trials, four of them are researching the magnesium effectiveness in pregnancy-associated muscle cramps. Two studies showed that therapy magnesium is efficiency in pregnancy-associated cramps with cramps during pregnancy, while other two studies didn't show any difference between treatment with magnesium, placebo or without any treatment. It was conducted quality assessment of systematic reviews using R-AMSTAR checklist. Cochrane systematic review had 42 of possible 44 points, and other systematic review had 40 points. Considering the similar number of points, systematic review lead to the same conclusion. Conclusion: Evidence of magnesium supplementation therapy on idiopathic skeletal muscle cramps or pregnancy- associated cramps were limited and contradictory. Based on this conclusion it is not justified to use magnesium for muscular cramps.