Magnesium can cause diarrhea with larger doses. On the other hand, calcium is constipating, so the two should balance each other. What dose are you taking??? The ideal dosage per pill is 333mg calcium & 167mg magnesium .. take 1 pill, 3 times a day. Normally I'd say take the third dose at bedtime, but if it's causing you distress, then best to take one pill at each meal, with food. Also make sure the supplement does not contain yeast, sugar, or starch. Effervescent mineral tablets often contain sorbitol, a sugar alcohol with notorious laxative effect.

Hope these suggestions are helpful

Doreen