Pyridoxine (Vitamin B6) has been investigated for its potential role in alleviating premenstrual syndrome (PMS) symptoms, including those of PMS Type H, which is often characterized by "hyperhydration" such as bloating and breast tenderness. The rationale for B6’s use is based on its involvement in neurotransmitter synthesis (notably serotonin and dopamine), as well as its possible influence on hormone metabolism and fluid balance. Several randomized controlled trials and systematic reviews have examined Vitamin B6 for PMS, with some studies indicating modest benefit in reducing overall PMS symptoms, particularly mood-related complaints and possibly bloating.

However, the quality of evidence is mixed. Many studies have limitations, including small sample sizes, inconsistent diagnostic criteria for PMS, and variations in dosing and formulation. A 1999 Cochrane review and subsequent updates have concluded that while B6 may be better than placebo for some PMS symptoms, the overall quality of evidence is low to moderate and the effect size is modest. Specific evidence for Type H PMS (hyperhydration) symptoms such as fluid retention is limited, though some women report subjective improvement in bloating.

In summary, there is some scientific basis for the use of Vitamin B6 in PMS, with limited but suggestive evidence for hyperhydration symptoms. The strength of evidence is moderate at best, justifying a rating of 2 out of 5. High doses of B6 can cause neuropathy, so dosing should be monitored.