How does exceeding the recommended dose of indigestion tablets cause symtoms?

Dose limit exceeded: Drug dosing is set by studies to establish the safest, most effective amount of medication for each indication treated. Short of toxic dosing, too much otc antacids can cause magnesium excess (with diarrhea), aluminum excess (with constipation), calcium excess (increased acid output). Otc doses of h2's or ppi's are typically an eighth to half the prescription strength. If in doubt, see a doctor.