Vitamin B6 (pyridoxal 5-phosphate) has been studied as a treatment for premenstrual syndrome (PMS), including PMS Type H, which is associated with hyperhydration symptoms like bloating, breast tenderness, and water retention. Scientific investigations, including double-blind, placebo-controlled trials, have explored the effects of Vitamin B6 supplementation on PMS symptoms. Some studies have found modest benefits in reducing overall PMS symptoms, including mood and physical complaints, though the magnitude of effect is generally small. The mechanism is thought to involve Vitamin B6's role as a cofactor in neurotransmitter synthesis (notably serotonin and dopamine) and in modulating hormone-related fluid retention.

Specifically for PMS Type H, evidence is limited and mixed. While some trials indicate improvement in bloating and breast discomfort, other studies find no significant benefit over placebo. The largest systematic reviews and meta-analyses (e.g., Cochrane Reviews) conclude that there is low-to-moderate quality evidence that Vitamin B6 may offer a small benefit for PMS overall, but the data for fluid retention symptoms (Type H) are less robust.

In summary, Vitamin B6 is used for PMS based on some scientific evidence, but the support is limited by small sample sizes, heterogeneity in study design, and variability in outcome measures. Its use for PMS Type H specifically is plausible but not strongly validated.