Vitamin B12 Side Effects

Although side effects with vitamin B12 are uncommon, they are possible. Reported side effects include blood clots in the legs, diarrhea, feelings of swelling over the entire body, and signs of an allergic reaction. Contact your healthcare provider right away if you experience any possible side effects while taking this vitamin.

An Introduction to Vitamin B12 Side Effects

Vitamin B12 is unlikely to cause side effects for most people, especially when used appropriately. However, a few possible side effects of vitamin B12 have been reported. Some of these side effects are not clearly linked to the vitamin, but they cannot be ruled out as possibly related to vitamin B12 use.

Possible Side Effects of Vitamin B12

Vitamin B12 side effects are uncommon. However, some of the possible side effects may include:
  • Diarrhea
  • Blood clots in the legs
  • Feelings of swelling over the entire body
  • Signs of an allergic reaction, such as:
    • Hives or a rash
    • Itching
    • Swelling of the lips, mouth, or throat
    • Wheezing or other difficulty breathing.
Let your healthcare provider know right away if you think you might be experiencing any of these possible side effects due to vitamin B12.

Final Thoughts on Vitamin B12 Side Effects

Vitamin B12 is relatively safe, especially if taken at normal doses. However, if you think you are experiencing vitamin B12 side effects, let your healthcare provider know. Also, let him or her know if you develop something that "just does not seem right." While it may not be related to vitamin B12, your healthcare provider will be able to diagnose and treat the problem.
Last reviewed by: Kristi Monson, PharmD
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