Can B12 help with fatigue?

Vitamin B12 is essential for red blood cell formation and nerve function, and a severe deficiency can cause fatigue. However, for individuals with normal B12 levels, supplementation has not been proven to improve general tiredness in well-conducted studies. Many people take B12 for energy without a deficiency—this is largely marketing, not evidence-based medicine. A home blood test can identify a deficiency, but a single result is not diagnostic and does not reveal the root cause of fatigue. Persistent tiredness warrants a medical workup including sleep, stress, iron status, and thyroid function. The evidence for B12 helping fatigue in non-deficient individuals is weak.