Vitamin B6 keeps appearing in PMS and PMDD research — and there's a specific neurochemical reason why. B6 in its active form (P5P) is the essential cofactor for serotonin, GABA, and dopamine synthesis — the exact neurotransmitters most disrupted in the luteal phase. This article breaks down what the research actually shows (including a BMJ systematic review of 9 trials and 940 women), why the form of B6 in your supplement matters, and what post-pill B6 depletion means for your mood. Evidence-led, no fluff.