B-Complex Vitamins

Reviewed by the HeyPsych Medical Review Board

Board-certified psychiatrists and mental health professionals

Published August 17, 2025•Updated February 20, 2026•Reviewed February 20, 2026

Indications

Primary Indications

Correction of B-vitamin deficienciesMegaloblastic anemia (B12 or folate related)Neuropathy associated with deficiencyAdjunctive mood and stress supportFatigue and low energy states

Mechanism

B vitamins act as essential cofactors in enzymatic reactions. Thiamine (B1) supports carbohydrate metabolism and nerve function; Riboflavin (B2) participates in redox reactions; Niacin (B3) forms NAD/NADP for energy metabolism; Pantothenic acid (B5) is a precursor to coenzyme A; Pyridoxine (B6) aids in neurotransmitter and heme synthesis; Biotin (B7) is required for carboxylase activity; Folate (B9) and B12 are crucial for DNA synthesis and homocysteine metabolism.

Dosing

Adult Dosing

deficiency: Varies by vitamin (e.g., B12 injections 1000 mcg/month, folate 400–1000 mcg/day)

usual range: Typical OTC complexes provide 50–100% of daily value for each B vitamin; therapeutic doses may be higher depending on deficiency state

Dosage Forms

Capsules
Tablets
Sublingual formulations
Injectable forms (B12, sometimes B-complex mixtures)

Onset Duration

Correction of deficiency symptoms may be seen in days to weeks. Neurological recovery from B12 deficiency may take months.

Adverse Effects

Common Side Effects

• Mild GI upset

• Flushing (niacin)

• Yellow discoloration of urine (riboflavin)

⚠️ Serious Side Effects

Neuropathy with very high B6 doses
Hepatotoxicity with high-dose niacin

Warnings

Critical Safety Information

→High-dose B6 (>200 mg/day) can cause sensory neuropathy.
→Niacin at therapeutic doses may cause hepatotoxicity and flushing.
→Excessive folate can mask B12 deficiency, risking neurological injury.

Interactions

With: Methotrexate

Risk: Interferes with folate metabolism

Action: Monitor closely

With: Anticonvulsants

Risk: Altered folate/B6 metabolism

Action: Monitor vitamin levels

With: Metformin

Risk: Reduced B12 absorption

Action: Monitor B12

Monitoring

Vitamin B12 and folate levels in at-risk patients
Homocysteine and methylmalonic acid (if deficiency suspected)
Liver function with high-dose niacin

Special Populations

👶Pregnancy

Folate supplementation strongly recommended; B-complex is safe at dietary doses

🤱Breastfeeding

Generally safe; supports maternal and infant needs

👧Children & Adolescents (Under 18)

Safe at recommended dietary allowances

👴Older Adults (65+)

B12 deficiency more common; consider higher supplementation

Tapering

No taper required; safe to discontinue when no longer needed.

Clinical Notes

B12 and folate are particularly critical in psychiatry and neurology due to their impact on mood and cognition.
Stress formulations often include higher doses of B5 (pantothenic acid) and B6 (pyridoxine).
High-dose injections are sometimes used in complementary medicine, though evidence is mixed.

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