4 min readNew DelhiMar 10, 2026 10:00 PM IST
Vitamin B12 supplements are often recommended to people who feel constantly tired or low on energy. The nutrient plays a crucial role in red blood cell formation, nerve function and energy production in the body. But what if a person becomes sleepy after taking the supplement? Is that normal?
According to Dr RR Dutta, HOD, Internal Medicine at Paras Health, Gurugram, vitamin B12 itself is generally not associated with drowsiness. In fact, the vitamin is linked with supporting energy production in the body.
“Mainly found in animal products, it plays an important role in red blood cell formation, nervous system health, and DNA synthesis, and provides aid to the body to produce energy,” asserts Dr Dutta. He adds that people who feel unusually tired after taking supplements should look at other possible factors.
“Patients or individuals experiencing unusual tiredness or fatigue after consuming vitamin B12 supplements should consider examining other possible factors, such as sleep quality, underlying medical conditions, or dietary habits.”
Why some people may feel sleepy after taking B12
If the body suffers from a persistent deficiency of Vitamin B12, there are chances it may cause potential mood changes such as sudden irritability or mild depression (Image: Pexels)
In certain situations, sleepiness after taking the supplement may be linked to other health conditions rather than the vitamin itself. “This is not a typical reaction, and can only occur in a few situations such as underlying medical conditions: anaemia, thyroid imbalance, dehydration, or high cortisol (a stress hormone in the body),” Dr Dutta explains.
He cites that sometimes people start these supplements while already experiencing fatigue or excessive tiredness due to an unknown medical condition, which can “relatively look like the B12 supplement is causing this symptom.”
He further explains that the body may go through an adjustment phase when supplementation begins, especially if a person was previously deficient. “The body gives signals that may look like rebalanced metabolic processes, leading to sleepiness.”
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However, in rare cases, “additives in the supplement or interactions with other medications” may contribute to these unusual symptoms. “If persistent sleepiness occurs after taking vitamin B12, it is advisable to consult a physician to assess vitamin levels and rule out other health concerns.”
Fatigue can also signal a vitamin B12 deficiency
Interestingly, excessive fatigue is also among the early symptoms of Vitamin B12 deficiency.
“The primary symptoms of Vitamin B12 deficiency are fatigue, excessive sleep, and constant tiredness. While these are early signs of the deficiency, if not treated over a period of time, it can potentially lead to pale skin, breathlessness, impaired focus, severe headaches, dizziness, and even memory issues,” Dr Dutta says.
This happens because vitamin B12 is essential for the production of healthy red blood cells that carry oxygen throughout the body. “When levels are low, oxygen delivery to tissues decreases, which can result in weakness, lethargy, and sometimes excessive sleepiness.”
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In some cases, a person may even feel tingling or numbness in the hands and feet due to low nervous system functioning. “If the body suffers from a persistent deficiency of Vitamin B12, there are chances it may cause potential mood changes such as sudden irritability or mild depression.”
DISCLAIMER: This article is based on information from the public domain and/or the experts we spoke to. Always consult your health practitioner before starting any routine.
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