What are the effects of excess Vitamin B12 (Cobalamin) on causing drowsiness?

Medical Advisory BoardAll articles are reviewed for accuracy by our Medical Advisory Board
Educational purpose only • Exercise caution as content is pending human review
Article Review Status
Submitted
Under Review
Approved

Last updated: May 9, 2025View editorial policy

Personalize

Help us tailor your experience

Which best describes you? Your choice helps us use language that's most understandable for you.

From the Research

Excessive vitamin B12 intake is unlikely to cause drowsiness, and if you're experiencing drowsiness, it's essential to consult with a healthcare provider to rule out other potential causes. The relationship between vitamin B12 and drowsiness is not well-established, and most studies focus on the consequences of deficiency rather than excess 1, 2, 3. Some studies suggest that high serum levels of vitamin B12 can be associated with various conditions, including solid neoplasia, hematological diseases, and liver disorders, but drowsiness is not a commonly reported symptom 4. It's crucial to note that vitamin B12 plays a vital role in cellular metabolism, and its deficiency can cause a range of symptoms, including fatigue and weakness, but excessive intake is not typically associated with drowsiness 5. Key points to consider include:

  • Most adults need only 2.4 micrograms of B12 daily, and taking significantly more than this amount may lead to side effects, although drowsiness is not a well-documented consequence.
  • If you're experiencing drowsiness, it's essential to consult with a healthcare provider to rule out other potential causes, as fatigue and drowsiness can be symptoms of many different conditions.
  • The timing of B12 supplementation may affect energy levels, and some people report that taking B12 earlier in the day rather than in the evening helps to minimize potential side effects.
  • If you're getting B12 through injections, discuss adjusting the frequency with your healthcare provider to ensure you're receiving the appropriate amount for your needs.

References

Research

Vitamin B12 Deficiency: Recognition and Management.

American family physician, 2017

Research

Vitamin B12 Deficiency: A Rare Cause of Excessive Daytime Sleepiness.

Journal of clinical sleep medicine : JCSM : official publication of the American Academy of Sleep Medicine, 2019

Research

Vitamin B12 deficiency.

Nature reviews. Disease primers, 2017

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

Have a follow-up question?

Our Medical A.I. is used by practicing medical doctors at top research institutions around the world. Ask any follow up question and get world-class guideline-backed answers instantly.