What Medications Can Cause Vitamin B12 Deficiency

Cobalamin, also known as vitamin B12, is important for a healthy body because it helps your body in  red blood cells and DNA production, and improves nerve function. There are a various reasons why you can become deficient in vitamin B12.1

Several medications can cause vitamin B12 deficiency,2 3 these are:

  • Metformin
  • Proton Pump Inhibitors (PPIs)
  • H2 Blockers
  • Oral Contraceptives

By the end of this article, you will have a solid understanding of what vitamin B12 deficiency is, the cause, treatment, and when to seek medical attention.

What is vitamin B12 deficiency 

Vitamin B12 deficiency occurs when your levels of vitamin B12 in the blood are below the healthy range. This can potentially cause your body to produce abnormally large red blood cells that can't function properly, this is called vitamin B12 deficiency anaemia.1

Anaemia is a term for having fewer red blood cells than normal or having abnormally low amounts of haemoglobin in the red blood cells. Haemoglobin is what helps red blood cells carry oxygen.4

Drugs are one of many causes of vitamin B12 deficiency. It is treatable through diet or B12 injections. 

Medications that can cause vitamin B12 deficiency

As with most medications, there can be unwanted effects. Whether you're on long or short-term medication. It is important to know what the side effects are and how to spot them.

Metformin - Given to people with type 2 diabetes, Metformin works by helping the person use insulin and reduces the person's blood sugar. It is the most commonly used medication in helping to treat diabetes and is both safe and effective. As beneficial as it is, it has the possibility of causing a vitamin B12 deficiency. It is thought that metformin causes this deficiency due to changing the way food moves through your intestine, bacterial overgrowth and reduced absorption of vitamin B12 within the small intestine. The risk, however, is linked to long-term use.2

Proton Pump Inhibitors - Given to people with a wide range of abdominal problems like heartburn or stomach ulcer. PPIs work by reducing the amount of acid being produced, helping to protect your stomach. Similar to metformin, long-term use of this medication increases the risk of vitamin B12 deficiency. This is thought to happen because of the way PPIs work. This can change the way some minerals and vitamins are absorbed.2

H2 Blockers - Given to people with a wide range of stomach problems like heartburn. H2 blockers also work by reducing the amount of stomach acid being produced, helping to protect your stomach. This can  cause malabsorption of some vitamins including vitamin B12. Similarly, the risk of vitamin B12 deficiency is linked to long-term use.2

Oral Contraceptives - Commonly known as birth control pills, are administered to women who want to prevent pregnancy. Oral contraceptives work by preventing fertilization. This medication reduces vitamin B12, however, has not been shown to cause vitamin B12 deficiency.3

There is a lot of controversy surrounding these drugs and vitamin B12 deficiency. One study suggests that although these medications decrease vitamin B12 they do not cause a significant enough decrease to require medical treatment.2

If you have other risk factors for developing vitamin B12 deficiency and are on one of these medications long-term keep an eye out for possible signs and symptoms of vitamin B12 deficiency.

Other causes

  • Digestive disorders like Crohn's. This disease is caused by your body's  system attacking healthy cells in your gut which destroys the lining and prevents the absorption of nutrients including vitamin B12
  • Unbalanced diet - Vitamin B12 is usually found in animal-related products so vegans are more likely to be at risk. The body is capable of storing vitamin B12 for 2 to 4 years so it takes time for any problems to develop if related to diet
  • Alcoholism. Drinking too much alcohol is bad for your health for some reasons. One of which is that it reduces your ability to absorb vitamin B12 because of heavy inflammation of the lining of your stomach and gut4
  • Functional B12 deficiency is when you have normal levels of vitamin B12 in the blood but your body can't transport and use the vitamin B12 properly
  • Pernicious anaemia is caused by your body's defence systems attacking cells in the stomach; it is the most common cause of vitamin B12 deficiency in the UK. This deficiency happens because vitamin B12 can not attach itself properly to the correct molecule in the stomach and struggles to be absorbed in the gut. This condition is most common in women over 60 years old3

Signs and symptoms

  • Fatigue
  • Nausea, Vomiting, Diarrhea 
  • Decrease appetite
  • Sore mouth
  • Yellowish skin
  • Numbness/Tingling in extremities
  • Vision problems
  • Memory problems
  • Speech difficulties
  • Feeling depressed/Irritable

Risk factors

Having members of your family with any diseases that affect the  gut can increase your risk of being vitamin-deficient, and also medication and lifestyle choices.


Neurological changes - These are changes that affect your central nervous system. This includes problems with your eyesight; memory and coordination. This can be potentially irreversible

Infertility - This means you may not be able to give birth, however, this change is usually reversible with appropriate B12 treatment

Stomach cancer - This complication is only if the cause of B12 deficiency is pernicious anaemia due to damage of the stomach

Neural tube defects - This is a birth defect due to lack of  B12 during pregnancy. The baby's spine, brain or skull does not develop properly3

Managing vitamin B12 deficiency

Natural remedies

Diet - Increasing the amount of B12 through diet can be done by eating foods high in B12. Foods naturally high in B12 include eggs, meat, fish and dairy. There are also many foods fortified with vitamin B12 such as breakfast cereals which of course are friendly for vegetarians and vegans.3


B12 Injection - There are two types of B12 injection, hydroxocobalamin and cyanocobalamin. Hydroxocobalamin stays in the body for longer and is usually the recommended option by doctors. This medication is usually given in vitamin B12 deficiency and you will continue to receive these injections especially if the deficiency is not caused by your diet.3

When to seek medical attention

Contact your GP if you are experiencing any of the symptoms listed in this article. They can do blood tests to see if you're B12 deficient and provide a treatment plan.


In conclusion, vitamin B12 is an essential vitamin which allows your body to function properly. The most common cause is pernicious anaemia. Medications can reduce levels of B12, but whether or not it causes a significant enough decrease to require treatment remains controversial. If you think you have a vitamin B12 deficiency, you can arrange for blood tests and treatment will be dietary changes or B12 injections depending on the cause.


  1. Ankar A, Kumar A. Vitamin b12 deficiency. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 [cited 2022 Oct 27]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK441923/
  2. Miller JW. Proton pump inhibitors, h2-receptor antagonists, metformin, and vitamin b-12 deficiency: clinical implications. Advances in Nutrition [Internet]. 2018 Jul 1 [cited 2022 Oct 27];9(4):511S-518S. Available from: https://academic.oup.com/advances/article/9/4/511S/5055945
  3. Berenson AB, Rahman M. Effect of hormonal contraceptives on vitamin B12 level and the association of the latter with bone mineral density. Contraception [Internet]. 2012 Nov 1 [cited 2022 Oct 27];86(5):481–7. Available from: https://www.contraceptionjournal.org/article/S0010-7824(12)00097-2/fulltext
  4. Vitamin B12 or folate deficiency anaemia [Internet]. nhs.uk. 2017 [cited 2022 Oct 27]. Available from: https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/
  5. Alcohol abuse & vitamin b12 [Internet]. Healthy Eating | SF Gate. [cited 2022 Oct 27]. Available from: https://healthyeating.sfgate.com/alcohol-abuse-vitamin-b12-10589.html
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Rob Reid

Master of Pharmacy - MPharm, Medway School of Pharmacy

Robert is a highly creative and technical individual with a strong scientific background and experience in both hospital and community pharmacy currently interning as a medical writer at Klarity.

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