It would be vary hard to OD on calcium. No one recommends more than 1800 mg a day to help control the diarrhea and it does work for many. It has some variables to consider if you take other meds to check to see if there is some interferance like with thyroid meds for one. Calcium is not really the cause of kidney stones either it has been know since the mid nineties that calcium may help to prevent them by getting rid of the oxilates which what cause the kidney stones in a lot of cases.You must take it regularly every day once you figure out the dose and stick to it and have the right form of calcium it can be a life changing thing to keep you out of the bathroom all the time.Linda