Interactions With Medications. Even though vitamin B-12 is safe if you take too much, it can interact negatively with certain medications. Chloramphenicol, a type of antibiotic, affects how your body responds to B-12.Even though you're taking a large dose of B-12, the medication limits the vitamin's function.ost vitamins and minerals can be toxic if you take too much. However, vitamin B-12 is a little different. Your system only absorbs a small amount at a time and gets rid of what it doesn't need, which means it's generally safe, even if you take too much.