 [ Symptoms ] i was 5 days late and now that i got its a brown color and i had unprotected sex while ovulating could i be pregnant [ Disease ] i think you mean micrograms mcg instead of milligrams mg if you really are taking 105mg that would equal 105 000mcg the recommended amount of vitamin b12 for adults is 2 4mcg but there is no upper limit set by the institute of medicine because no adverse effects have been found with taking excess vitamin b12 because it is a water soluble vitamin it is potential for toxicity is low most people get enough from diet unless they are vegetarians older or have a health condition that decreases the absorption of vitamin b12 for more on proper dosing and side effects see this webmd page