B12
Over-the-counterWhat is B12?
Vitamin B12, also called cobalamin, is a water-soluble vitamin that your body needs for many essential functions. Your body cannot make B12 on its own. You must get it from food or supplements. B12 plays a key role in forming red blood cells, supporting nerve function, and making DNA.
Many people do not get enough B12 from their diet alone. Older adults, vegetarians, vegans, and people with certain digestive conditions often have low B12 levels. Taking a B12 supplement can help fill this gap. B12 supplements come in several forms including tablets, sublingual lozenges, and injections.
B12 deficiency can cause fatigue, weakness, nerve problems, and a type of anemia called megaloblastic anemia. Catching and treating low B12 levels early helps prevent these problems. Regular blood testing can show if your B12 levels are where they should be.
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Common uses
- Treating and preventing vitamin B12 deficiency
- Supporting healthy red blood cell formation
- Maintaining nerve function and preventing nerve damage
- Reducing fatigue and increasing energy in people with low B12
- Supporting brain health and cognitive function
- Helping lower homocysteine levels, which may benefit heart health
- Supporting healthy pregnancy and fetal development
How it works
B12 works as a cofactor for two important enzymes in your body. The first enzyme, methionine synthase, helps convert homocysteine into methionine, an amino acid your body needs. This process also helps produce compounds needed for DNA synthesis and cell division. The second enzyme, methylmalonyl-CoA mutase, is essential for breaking down certain fats and amino acids for energy.
When you take a B12 supplement, your body absorbs it in your small intestine with help from a protein called intrinsic factor. Some people lack intrinsic factor or have conditions that block B12 absorption. These people may need higher doses or B12 injections that bypass the digestive system. Once absorbed, B12 travels through your bloodstream to cells throughout your body where it performs its vital functions.
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Dosage information
The recommended daily amount of B12 for most adults is 2.4 micrograms. Pregnant women need 2.6 micrograms daily, and breastfeeding women need 2.8 micrograms. Over-the-counter B12 supplements typically contain much higher doses, ranging from 500 to 5,000 micrograms per tablet. Higher doses are often used because only a small percentage of oral B12 is absorbed. B12 is considered very safe because it is water-soluble and excess amounts leave your body through urine. Always follow the directions on the product label or ask your pharmacist for guidance.
Side effects
- Mild diarrhea
- Itching or rash
- Headache
- Nausea or upset stomach
- Dizziness
B12 supplements are generally very safe with few side effects. Serious side effects are rare but can include signs of an allergic reaction such as severe rash, swelling of the face or throat, or difficulty breathing. If you experience these symptoms, seek medical attention right away. Some people report feeling more energized when they start B12, which is usually a positive sign that their body needed it.
Drug interactions
- Metformin for diabetes may lower B12 levels over time
- Proton pump inhibitors like omeprazole can reduce B12 absorption
- H2 blockers such as famotidine may decrease B12 absorption
- Chloramphenicol antibiotic may reduce B12 effectiveness
- Colchicine for gout can interfere with B12 absorption
- High doses of vitamin C may destroy B12 in supplements if taken together
- Alcohol use can reduce B12 absorption and storage
Blood test monitoring
Blood testing helps confirm whether your B12 levels are in a healthy range. A standard B12 blood test measures the amount of vitamin B12 in your bloodstream. Normal levels are typically between 200 and 900 picograms per milliliter. However, some people have symptoms of deficiency even at levels above 200. Two other markers can provide additional information. MCV, or mean corpuscular volume, measures the size of your red blood cells. High MCV can indicate B12 deficiency. Homocysteine is an amino acid that rises when B12 is low. Checking all three markers gives a clearer picture of your B12 status and whether supplementation is working.
Related blood tests
Taking B12? Monitor your levels.
- Track how your body responds
- Catch side effects early with blood work
- Share results with your doctor
Frequently asked questions
Yes, B12 supplements are available over the counter at Rite Aid and other pharmacies. You do not need a prescription to purchase B12 tablets, sublingual lozenges, or liquid forms. However, B12 injections typically require a prescription from your doctor.
Most people begin feeling better within a few days to a few weeks of starting B12 supplements. Energy levels often improve first. Nerve symptoms may take several weeks or months to improve. Blood test results typically show improvement within 4 to 8 weeks of daily supplementation.
Most people take B12 in the morning because it can increase energy levels. Some people find that taking it at night keeps them awake. B12 can be taken with or without food. Choose a time that works best for your routine and stick with it daily.
Three blood tests help monitor your B12 status. A B12 blood test measures vitamin levels directly. MCV checks your red blood cell size, which increases when B12 is low. Homocysteine levels decrease when B12 therapy is working. Testing these markers every 3 to 6 months helps confirm your supplement dose is right for you.
Several groups have higher risk of B12 deficiency. Vegetarians and vegans get little or no B12 from their diet. Adults over 50 often absorb B12 poorly. People with digestive conditions like Crohn's disease or celiac disease may not absorb enough B12. Anyone taking metformin or acid-reducing medications should monitor their B12 levels regularly.
Common forms include cyanocobalamin and methylcobalamin. Cyanocobalamin is synthetic, stable, and well-studied. Methylcobalamin is a natural form that some people prefer. Both forms work well for most people. Sublingual tablets dissolve under your tongue and may absorb slightly better than regular tablets.
B12 is very safe because it is water-soluble. Your body removes excess B12 through urine. There is no established upper limit for B12 intake. Even high doses of 1,000 to 2,000 micrograms daily are considered safe for most people.
Common signs include tiredness, weakness, and pale skin. You may experience tingling or numbness in your hands and feet. Some people have trouble with balance or memory. Mood changes and difficulty concentrating can also occur. If you have these symptoms, ask your doctor about B12 testing.
Most people who eat meat, fish, eggs, and dairy get enough B12 from food. However, older adults and people with certain health conditions may still become deficient. Digestive problems can prevent B12 absorption even with adequate dietary intake. Blood testing can show if you need supplementation regardless of your diet.
Rite Aid offers blood testing services that measure over 200 biomarkers including B12, MCV, and homocysteine. The service costs $349 per year and includes 2 comprehensive tests. Regular testing helps you track whether your B12 levels are improving with supplementation. You can use these results to adjust your supplement dose with your doctor's guidance.