Your blood cells and nerves rely on vitamin B-12 to form and function properly. Daily recommended doses of vitamin B-12 range from 0.4 to 2.8 micrograms, depending on your age and health status, according to the Office of Dietary Supplements. Before taking vitamin B-12 supplements, discuss the potential drug interactions associated with this nutrient.
Avoid taking vitamin B-12 supplements if you are receiving long-term treatment with chloramphenicol, a type of broad-spectrum antibiotic. Chloramphenicol may reduce the effectiveness of vitamin B-12, which may limit your body's ability to produce new blood cells. In the absence of proper blood cell formation, your body may have difficult transporting oxygen to your organs or protecting itself against infectious pathogens.
Avoid taking vitamin B-12 at the same time as tetracycline antibiotics. Vitamin B-12 may reduce your body's ability to absorb this medication, which can reduce the effectiveness of tetracycline. Take vitamin B-12 at a different time of day from tetracycline to help prevent this drug interaction.
Other medications may actually lower your blood levels of vitamin B-12 and can reduce the effectiveness of vitamin B-12 supplements. Such medications include medications to reduce stomach acid, such as H2 blockers and proton pump inhibitors, diabetes medication, such as metformin, and cholesterol lowering medications, such as bile acid sequestrants. Anticonvulsants, chemotherapy drugs and colchicine may also decrease the levels of B-12 in your body. If you're using any of these medications, your doctor may advise increasing your vitamin B-12 intake to ensure you get enough of this nutrient.
Vitamin B-12 supplements are deemed generally well tolerated and are not known to cause side effects -- even at high doses. Seek care from your doctor, however, if you develop any unusual health problems while taking vitamin B-12. In addition, children and pregnant or breast-feeding women shouldn't use vitamin B-12 supplements without first consulting a doctor.