Vitamin B-Complex
Commonly used for
EnergyNutrition
Where to Buy
Our experts personally review each product we recommend for quality and cost effectiveness.
The cheapest product is usually low quality, but more expensive doesn’t always mean better.
The cheapest product is usually low quality, but more expensive doesn’t always mean better.
What is it? / Overview
B vitamins act as coenzymes in energy metabolism and in homocysteine remethylation; correcting a genuine deficiency (common in restrictive diets, heavy alcohol use, malabsorption, or aging) restores these pathways and can relieve related fatigue or neurologic symptoms. In someone already replete, extra B vitamins add little -- the cognitive benefit seen in trials is real but small, and driven mainly by people with elevated homocysteine or low baseline B-vitamin status.
How is it used? / Administration
Form: Combination of B1, B2, B3, B5, B6, B7, B9 (folate), B12 at roughly RDA-to-modest-multiple levels; 'activated'/methylated forms available
Typical dose studied: One daily serving
Timing: With food, earlier in the day (water-soluble; some find it mildly stimulating)
Harmless bright-yellow urine from riboflavin is expected, not a side effect to worry about. High-dose folate in the blend can mask a B12 deficiency's hematologic signs -- pair with adequate B12.
How well does it work? / Evidence
~ Moderate evidence
Who should avoid it?
Interacts with: Levodopa (without carbidopa) -- B6 reduces its efficacy; Phenytoin, phenobarbital -- B6 may reduce drug levels; Methotrexate, antiepileptics -- folate component may interact
Already taking it? Reasonable to continue if well tolerated; chronic high-dose B6 (roughly 50-100+ mg/day long-term) has been linked to sensory peripheral neuropathy, so check the label doesn't run unusually high.
Research & references
Wang Z et al. (2022). B Vitamins and Prevention of Cognitive Decline and Incident Dementia: A Systematic Review and Meta-Analysis. Nutrition Reviews. Berg J et al. (2025). Efficacy of B Vitamin Supplementation on Global Cognitive Function in Older Adults: A Systematic Review and Meta-Analysis. Nutrition Reviews. Han A et al. (2025). Exploring Neuropsychiatric Manifestations of Vitamin B Complex Deficiencies. Frontiers in Psychiatry.
Disclosure: Knozela is a participant in the Amazon Associates affiliate program. Some "Where to buy" links on this page are affiliate links -- if you make a purchase through them, Knozela may earn a commission at no additional cost to you.