Should You Take Vitamin B12 Supplements If You Take Metformin? - GoodRx (2024)

Certain prescription and over-the-counter (OTC) medications can cause vitamin deficiencies. If you’re currently taking metformin for Type 2 diabetes, you and your healthcare provider may have already discussed your vitamin B12 levels.

That’s because metformin can lead to vitamin B12 deficiency (low vitamin B12) in some cases. In fact, scientists first discovered in 1969 that people taking metformin for 3 months or more had difficulty absorbing vitamin B12. This can turn problematic — vitamin B12 deficiency can cause certain health problems, like anemia and nerve damage, if left untreated. Thankfully, there are OTC and prescription vitamin B12 products that can help prevent and treat low vitamin B12 levels when needed.

Read on to learn more about metformin, how it affects vitamin B12, and if you need to take a vitamin B12 supplement alongside metformin.

What is metformin?

Metformin is a FDA-approved prescription medication. It’s a first-choice option for treating high blood sugar levels — along with diet and exercise — in people ages 10 and older with Type 2 diabetes. An extended-release (ER) version of metformin is also FDA-approved for adults only.

Metformin is an oral medication available in the following immediate-release (IR) and ER forms:

• Metformin IR tablets: 500 mg, 850 mg, and 1,000 mg

• Metformin IR oral solution (Riomet): 500 mg/5 mL

• Metformin ER tablets: 500 mg and 750 mg

• Metformin ER (Glumetza) tablets: 500 mg and 1,000 mg

• Metformin ER (Fortamet) tablets: 500 mg and 1,000 mg

Metformin is also available in combination with other medications to treat Type 2 diabetes. And besides Type 2 diabetes, metformin is also used off-label to treat other health conditions, such as:

• Prediabetes

• Gestational diabetes

• Weight gain from antipsychotic medications

• Polycystic ovary syndrome (PCOS)

What is vitamin B12?

Vitamin B12 — also known as cobalamin — is a water soluble vitamin that helps support your body’s blood and nerve cells. It also helps your body make DNA.

In most cases, you can get enough vitamin B12 through your diet alone. Vitamin B12 is found in a variety of foods and drinks, such as:

• Beef

• Seafood

• Poultry

• Dairy products

• Nutritional yeast

• Breakfast cereals

• Plant-based milks, like almond, coconut, and soy milk

Vitamin B12 supplements and medications

When needed, you can take vitamin B12 (cyanocobalamin) as a dietary supplement. It’s available in oral and sublingual (under the tongue) forms to prevent and treat vitamin B12 deficiency. You can find these products at your local pharmacy, grocery store, or online. Products may include vitamin B12 by itself, and it can also be found as part of a multivitamin or B complex vitamin.

Dietary supplements contain different amounts of vitamin B12 depending on the product:

• Multivitamin: 5 mcg to 25 mcg

• B-complex vitamins: 50 mcg to 500 mcg

• Vitamin B12 only: 500 mcg to 1,000 mcg

Vitamin B12 is also FDA approved as medication for treating vitamin B12 deficiency as a prescription nasal spray and injection. Nascobal (cyanocobalamin nasal spray) comes as 500 mcg/spray nasal spray. The injection is available as cyanocobalamin 1,000 mcg/mL.

How does metformin affect vitamin B12 levels?

Metformin can lower the absorption of vitamin B12 in your small intestines. This can sometimes, but not always, lead to vitamin B12 deficiency. Health experts are still studying how metformin does this, but these are some of the main theories:

• By causing changes in how calcium binds to vitamin B12

• By causing more vitamin B12 to be held by the liver

• By promoting digestion changes

• By lowering amount of intrinsic factor in your stomach (intrinsic factor is needed to absorb vitamin B12)

• By contributing to higher amounts of bacteria in the intestines

It’s also unclear how often metformin causes vitamin B12 levels to drop too low. Vitamin B12 deficiency from metformin happened to about 6% to 50% of people in various studies — a wide range. But it appears that using high doses of metformin for a long time contributes to vitamin B12 deficiency more frequently.

Does vitamin B12 interfere with metformin?

No. Vitamin B12 supplements don’t interact with metformin, so they can safely be taken together.

However, it’s always a good idea to keep a current list of all your prescription and OTC medications. This helps your healthcare provider and pharmacist make sure there are no interactions to be concerned about.

How do I know if my B12 levels are too low?

Blood tests can help determine if your vitamin B12 levels are too low.

Vitamin B12 levels at less than 200 pg/mL generally suggest a vitamin B12 deficiency. Your healthcare provider may also check methylmalonic acid (MMA) levels in your blood or urine. Your body makes extra MMA if it doesn’t have enough vitamin B12.

Blood tests aside, symptoms you’re experiencing can also give you an idea about your vitamin B12 levels.

Symptoms of low B12 levels

Symptoms of vitamin B12 deficiency include:

• Pale skin

• Feeling weak or tired

• Dizziness

• Fast or irregular heartbeat

• Tingling in the feet and hands (nerve pain)

• Shortness of breath

Contact your healthcare provider if you’re experiencing any of these symptoms. Depending on the situation, they may decide to check your vitamin B12 levels.

How often should my vitamin B12 levels be monitored if I take metformin?

Keeping track of different blood tests can be overwhelming. Luckily, your healthcare provider can help with this.

If you’ve been prescribed metformin, the American Diabetes Association recommends that your vitamin B12 levels should be checked at your first diabetes office visit. Your healthcare provider should then check your vitamin B12 levels at least once a year after that.

Should you take vitamin B12 supplements if you take metformin?

Not typically. You should only do so if your healthcare provider tells you to.

If you’re concerned about your vitamin B12 levels, making sure you consume enough vitamin B12 in your diet is a good first step. And if you take a multivitamin already, check its “Drug Facts” label to see if it contains vitamin B12.

If you're instructed to take a vitamin B12 supplement, that’s the time to take action. It’s important to correct your B12 levels to avoid developing health problems down the road. Make sure to ask your healthcare provider about what type and dose of vitamin B12 you should take.

Some studies suggest that oral and injection forms of vitamin B12 have similar effectiveness. Results from one study showed the sublingual form of vitamin B12 works as well and may be even more effective than the injection. But vitamin B12 injections are typically absorbed better and work faster for people with severe deficiency caused by malabsorption.