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Vitamin B12 Side Effects & What They Mean


Vitamin B12 side effects - Dr. Axe

Vitamin B12, also known as cobalamin, is an important water-soluble vitamin that plays a central role in several aspects of health, including brain function, red blood cell formation and DNA synthesis. It’s also considered an “essential nutrient” because your body is unable to produce it on its own and needs to obtain it from food sources or supplementation. In recent years, research has unearthed a number of vitamin B12 side effects, including positive effects, such as its ability to improve energy levels, enhance mood and keep your heart healthy.

Although incorporating a good variety of vitamin B12 foods in the diet can help most people meet their needs for cobalamin, supplementation is sometimes necessary for those who may have underlying health conditions or take certain medications. Like all supplements, however, there are several vitamin B12 benefits and side effects to consider.

So what are the side effects of vitamin B12? How can you minimize these potential vitamin B12 side effects while maximizing the benefits? Here’s what you need to know.

Positive Vitamin B12 Side Effects

Does B12 have side effects? What does B12 do for your body? Here are a few of the top vitamin B12 benefits for men and women:

1. Prevents Deficiency

Taking a vitamin B12 supplement is one of the easiest and most effective ways to prevent a vitamin B12 deficiency, especially if you don’t regularly consume foods high in this important water-soluble vitamin. Some of the most common side effects of vitamin B12 deficiency include weakness, anemia, constipation, decreased appetite and unintentional weight loss.

2. May Boost Energy Levels

Vitamin B12 plays an integral role in energy production and is essential for converting the foods that you eat into a form of  energy that can be used by the body. It’s also necessary for the formation of red blood cells, which help supply the cells with oxygen so they can function properly. While research is lacking on whether taking a vitamin B12 supplement can improve energy levels on its own, it can aid in energy production and may be especially beneficial for boosting energy levels if you’re lacking in this key micronutrient.

3. Supports Growth and Development

Vitamin B12 is absolutely essential during pregnancy for ensuring healthy fetal growth and development. Not only is vitamin B12 crucial for preventing birth defects, but a deficiency may also increase the risk of miscarriage or premature birth. For this reason, vitamin B12 is a common component of most prenatal vitamins and can also be found in many fortified foods.

4. Keeps Skin, Hair and Nails Healthy

Some of the most visible signs of vitamin B12 deficiency can be spotted right in your hair, skin and nails. In fact, some of the most common symptoms of deficiency include hyperpigmentation of  the skin and nails, hair changes, vitiligo, and angular stomatitis, which is a condition that causes cracks and inflammation in the corners of the mouth. Fortunately, several case reports have found that these changes may be reversible by correcting the deficiency with supplementation.

5. Improves Mood

One of the most surprising vitamin B12 injections side effects is the ability to improve mood and mental health. This is because vitamin B12 acts as a cofactor for neurotransmitters like serotonin and dopamine, both of which are key regulators of mood and emotion. Preliminary research also shows that pairing vitamin B12 supplementation with antidepressants could help significantly reduce symptoms of major depressive disorder to a greater extent than treatment with an antidepressant alone.

6. Promotes Heart Health

Vitamin B12 is important for the metabolism of homocysteine, a type of amino acid in the blood that may be tied to a higher risk of heart disease. In addition to decreasing homocysteine levels, which could potentially help reduce the risk of heart disease. Some research also indicates that higher vitamin B12 levels could be linked to improved outcomes for those who have suffered from an ischemic stroke and may be associated with a lower risk of coronary artery disease.

Negative Vitamin B12 Side Effects

Despite the multitude of benefits associated with vitamin B12, can too much vitamin B12 be harmful? What happens when you have too much vitamin B12 in your body? Vitamin B12 is a water-soluble vitamin, which means that excess amounts are flushed out of the body through the urine, making a vitamin B12 overdose nearly impossible.

However, while vitamin B12 is safe when used as recommended, there are several vitamin B12 injection side effects to consider as well. Some of the most common vitamin B12 shot side effects include:

  • Headache
  • Dizziness
  • Rash
  • Itchy skin
  • Facial flushing
  • Skin redness
  • Cold symptoms
  • Anxiety
  • Swelling
  • Diarrhea
  • Vomiting
  • Numbness
  • High blood pressure

How to Prevent Vitamin B12 Side Effects

The best way to avoid the potential side effects of too much vitamin B12 is to get the majority of your vitamin B12 from nutrient-rich food sources, including meat, poultry, seafood and dairy products. Enjoying these foods alongside a variety of other healthy ingredients as part of a balanced diet can help ensure you meet your needs and reduce the risk of too much vitamin B12 side effects.

In some cases, supplementation may be necessary, especially if you don’t regularly consume foods high in vitamin B12 or have issues with vitamin absorption. In that case, be sure to stick to the recommended vitamin B12 dosage and use only as directed. If negative vitamin B12 supplement side effects persist, consider decreasing your dosage or consult with your doctor.


Supplementing with vitamin B12 may not be right for everyone and can even be contraindicated in some cases due to the potential vitamin B12 side effects. For example, those with high blood pressure, heart problems, skin conditions, blood disorders, gout and low potassium levels should use vitamin B12 with caution and may want to consider talking to a trusted health care practitioner before starting supplementation.

Certain medications or supplements can also interfere with vitamin B12 supplements. What medications should not be taken with B12? Folic acid, potassium, vitamin C and chloramphenicol, a type of broad-spectrum antibiotic, may all interfere with vitamin B12 in the body.

In order to minimize vitamin B12 supplements side effects, it’s best to stick to the recommended dosage and use as directed. If you experience any persistent vitamin B12 tablets side effects or serious symptoms, talk to your doctor to determine the best course of treatment for you.

Read Next: Vitamin B: Top 6 Benefits of B Vitamins & How to Get More in Your Diet

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