Magnesium citrate, while fairly effective, is used as a laxative, and so can cause D.
According to the following link, the chelated forms are more expensive but best, causing fewer side effects:
magnesium potassium aspartate
The kind I took, magnesium aspartate, caused D. Don't know what kind my daughter took. The magnesium oxide is supposed to be the least effective.
Daughter (22) Dx'd Crohn's 3/06. Misdiagnosed for two years, including by top pediatric Crohn's specialist as stress. No symptoms for the past two years. Recent colonoscopy shows stricture gone but still two spots of inflammation in TI. Used LDN to taper off Entocort. Was on Entocort since April 06. Never had D. 4.5 mg LDN, SCD multivit, homemade yogurt, 5000IU vit D3, 500 mg calcium, 27 mg iron, monthly B12 shots, daily oral B12 1000. SCD diet modified to include potatoes and rice.