Symptoms of vitamin B12 toxicity
Pro Research Analysisby 
Searched over 200M research papers
Vitamin B12 Toxicity Symptoms: Clinical Case Insights
While vitamin B12 deficiency is well-documented, reports of vitamin B12 toxicity are rare. However, there is evidence that excessive intake can lead to certain symptoms. In a documented case, a young woman treated with multiple high oral doses of cyanocobalamin (vitamin B12) developed a range of symptoms after a cumulative dose of 12 mg. These symptoms included acne, palpitations, anxiety, akathisia (a feeling of inner restlessness), facial redness, headache, and insomnia. Importantly, these symptoms resolved within two weeks after stopping the vitamin B12 supplementation, and there were no lasting complications or sequelae. This case highlights that, although uncommon, vitamin B12 toxicity can present with noticeable but reversible symptoms when very high doses are consumed over a short period .
Lack of Widespread Reports and Clinical Relevance
Most research and clinical guidelines focus on the consequences of vitamin B12 deficiency, which can cause a wide range of hematological, neurological, and psychiatric symptoms, but do not report toxicity symptoms from excess intake in typical dietary or supplemental amounts 23456789+1 MORE. The case above remains an exception rather than the rule, and there is no evidence of severe or life-threatening toxicity from vitamin B12 in the general population.
Conclusion
Symptoms of vitamin B12 toxicity are rare and generally mild, with reported cases showing reversible effects such as skin changes, palpitations, anxiety, and sleep disturbances after very high doses. For most people, vitamin B12 supplementation is safe, and toxicity is not a common clinical concern. However, as with any supplement, excessive intake should be avoided unless specifically recommended and monitored by a healthcare professional .
Sources and full results
Most relevant research papers on this topic