Pyridoxal 5-phosphate (P5P)

Tier 2 — promising · Vitamin B6 · Neurotransmitters · Homocysteine

The bioactive coenzyme form of vitamin B6 that bypasses the hepatic conversion pyridoxine HCl requires. Preferred in those with impaired hepatic function, aldehyde oxidase deficiency, or on drugs that inhibit B6 conversion. Essential cofactor for over 140 enzymatic reactions including neurotransmitter synthesis (GABA, serotonin, dopamine), homocysteine methylation, and haem formation. Chronic high-dose pyridoxine HCl (>200 mg/day long-term) causes sensory neuropathy — P5P does not appear to carry the same risk but caution still warranted.

Dose: 20–50 mg P5P daily; up to 100 mg short-term for specific indications