 [ Symptoms ] does b12 2500 mcg causes bloody stool  i just started taking sublingual vitamin b12 methylcobalamin and noticed that my stool is bloody is this a normal reaction to the vitamin [ 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 symptoms of overdose may include severe stomach pain extreme drowsiness seizures