 [ Symptoms ] can b 12 cause leg cramps  since my husband started taking b 12 he has been getting severe leg cramps [ Disease ] if overdose is suspected contact a poison control center or emergency room immediately us residents can call the us national poison hotline at 1 800 222 1222 canada residents can call a provincial poison control center overdose can cause lactic acidosis symptoms of overdose may include severe drowsiness severe nauseavomitingdiarrhea rapid breathing slowirregular heartbeat