Magnesium deficiency causes muscle spasms and cramps. That's a fact. If you're experiencing muscle cramps due to low magnesium then adding a supplement will al

Magnesium deficiency causes muscle spasms and cramps. That's a fact. If you're experiencing muscle cramps due to low magnesium then adding a supplement will almost certainly fix the problem. If you're experiencing muscle cramps for another reason, it won't work, probably. But supplements are cheap and low risk, so it's a good thing to try first. A more accurate statement would be "there is no scientific proof that Mg works against cramps [absent a Mg deficiency]."