Vitamin B12 is an essential nutrient that is commonly taken as an oral supplement. However, it has the potential to interact with several medications, including metformin and colchicine. It’s important to understand the interactions that can occur with vitamin B12 in order to get the most benefit out of taking vitamin B12. Otherwise, there is an increased risk of worsening vitamin B12 deficiency. Drug interactions with vitamin B12 could lead to worsened symptoms, such as lack of energy, problems with memory, and digestive issues. 

So, which medicines can interact with vitamin B12? Continue reading to learn more about what medicines may need to be avoided while taking a vitamin B12 supplement.

Vitamin B12 Can Interact With Certain Medications

The following medications may decrease vitamin B12 levels in the body.


Chloramphenicol, known by the brand names Chloromycetin and Viceton, is an antibiotic used to treat superficial eye infections, swimmer’s ear, and Typhoid fever, among other infections. Although it is an effective antibiotic, it can cause dose-related adverse effects, such as bone marrow suppression. Fewer red blood cells produced in the bone marrow means less vitamin B12 is used by available red blood cells. When chloramphenicol is taken with vitamin B12, less vitamin B12 may be absorbed and utilized in the body. 


Colchicine, or Colcrys, is an anti-inflammatory medication used to treat gout attacks. It can interfere with certain receptors in the lining of the small intestine that are involved with the absorption of vitamin B12. Vitamin B12 levels may need to be monitored while taking a medication like colchicine. 


Metformin, also known as Glucophage, is a commonly prescribed medication for type 2 diabetes. While it is not known to have many severe side effects, it can interact with vitamin B12, and long-term use of metformin has been associated with decreased vitamin B12 levels. This is because metformin can block the absorption of vitamin B12 in the gastrointestinal tract, which can increase the risk of vitamin B12 deficiency. On average, 6% to 30% of people taking metformin may have vitamin B12 deficiency. Therefore, vitamin B12 levels may need to be monitored in those taking metformin. 


Alcohol consumption has been shown to affect vitamin B12 levels. Even moderate consumption of alcohol can irritate the lining of the stomach, which can lead to reduced acid production. Vitamin B12 requires acid in the stomach and a protein called intrinsic factor to be absorbed adequately. Alcohol can ultimately alter how vitamin B12 is absorbed. Studies have shown that over 8 weeks of moderate alcohol consumption, vitamin B12 levels can decrease over time. 

H2 blockers 

H2 blockers are sometimes referred to as H2 antagonists and include drugs like Zantac (ranitidine) and Pepcid (famotidine). These drugs are used to treat heartburn and stomach ulcers by decreasing acid production in the stomach. A decrease in stomach acid can lead to decreased absorption of vitamin B12.   

Proton pump inhibitors

Proton pump inhibitors, also known as PPIs, include drugs like Prilosec (omeprazole) and Prevacid (lansoprazole). Like H2 blockers, PPIs can help treat stomach ulcers and symptoms of gastrointestinal reflux disease (GERD). Because they primarily work by decreasing stomach acid production, these drugs can decrease the absorption of vitamin B12 in the body. It’s important to monitor vitamin B12 levels if you’re taking a PPI, especially if you are vitamin B12 deficient. 


Dilantin (Phenytoin), Tegretol (carbamazepine), and Depakote (valproate) are anticonvulsants, or medications used to treat seizures. These drugs may affect the metabolism, or the processing, of vitamin B12 in the body. Studies have shown that anticonvulsant drugs can decrease folate and vitamin B12 levels in the body. 

Bile acid sequestrants 

Bile acid sequestrants are cholesterol-lowering drugs. They work by absorbing cholesterol molecules in the intestine and promoting the elimination of bile acids in the stool. Bile acid sequestrants include Questran (cholestyramine) and Colestid (colestipol), and they may interfere with the absorption of calcium, folate, iron, and vitamins, including vitamin B12. Taking bile acid sequestrants with vitamin B12 supplements may lead to a decrease in vitamin B12 in the body, which could increase the risk of vitamin B12 deficiency. 

Bottom Line

As an important vitamin for the production and maintenance of red blood cells, nerve cells, and DNA, vitamin B12 is required for optimal health. While it can be acquired through the diet, vitamin B12 is often recommended as a supplement, especially for vegans and vegetarians who may have trouble getting enough vitamin B12 from their diet. However, if you’re also taking other medications like metformin or colchicine, it is important to be aware of potential drug interactions. 

If you have further questions about vitamin B12 supplementation, you can contact the team at Medical Weight Loss Centers of America. Experts are available to help determine whether vitamin B12 supplements may be right for you and your health goals. Because of the risk of drug interactions with oral vitamin B12, a healthcare professional may recommend vitamin B12 shots instead.