Vitamin B Complex

B Vitamins

Snapshot

Indications	Contraindications
Homocysteine lowering¹ Stroke risk¹ Depression adjunct² Slowing cognitive decline³ Peripheral neuropathy⁴ Exercise fatigue⁵ Acute low back pain adjunct⁶	Soy allergy⁷ Impaired renal function (cyanocobalamin)⁸

Vitamin B complex combines eight water-soluble vitamins that act as cofactors in energy metabolism, neurotransmitter synthesis, and the building of genetic material⁹. Supplementation is used to lower homocysteine and as an adjunct for depressive symptoms, cognitive decline³, peripheral neuropathy, and exercise fatigue. Older adults, whose food intake and absorption decline, are the typical patients⁹.

The evidence is split. A 2022 meta-analysis found B vitamin supplementation slowed cognitive decline slightly, mainly in people without dementia and in trials lasting over 12 months³. Stroke risk fell modestly overall with homocysteine-lowering B vitamins, but the benefit depended on folic acid fortification policy and kidney function¹. A 2024 systematic review in oncology found vitamin B6 and B12 with acupuncture effective as adjuncts for chemotherapy-induced peripheral neuropathy in two small studies, and it called for large randomized trials¹⁰. Products list vitamin B complex as multi-vitamin B formulas or as single vitamins in different forms; see Form comparison.

In impaired renal function, cyanocobalamin can accelerate renal decline, which is why other B12 forms are under study in that group⁸. LiverTox rates high-dose niacin as a well-known cause of clinically apparent liver injury and the other B vitamins as unlikely causes¹¹.

Last updated October 16, 2026. Read how we make monographs.

In the full monograph

84 sources, 66 studies

When to useThe situations practitioners use it for, each with the reason and the study behind it.
SafetyWho should avoid it, who needs extra care, and the side effects reported in studies.
InteractionsThe medicines and supplements it interacts with, the effect of each, and what labeling says to watch.
Protocol notesThe doses used in studies, how and when they were taken, and how the forms on the market compare.
How it worksWhat it is and how it works in the body, in plain terms.
Published studiesThe studies behind each use, popular claims checked against them, and trials still under way.
Word of mouthWhat patients and practitioners report online, kept separate from the clinical evidence.
Clinical perspectiveA closing read of where the evidence is solid, where it is thin, and what has not been studied.

Snapshot

In the full monograph

Sources