Effective, but it also reliably messes up my stomach
Magnesium Oxide and Magnesium Citrate also do that to me. Magnesium Glycinate (and especially Magnesium Threonate) seem to be a lot better in that regard. It also seems to help to take 25% RDA in the morning and 25% at night, rather than 100% RDA at any one time.
How do you keep them in check?
Magnesium glycinate!
Light and noise sensitivity can be early indicators one needs additional magnesium, especially if preceded by vomiting, fever or sweating.