Doctors usually start with a treatment that will have the fewest side-effects. If it works, good. If not men something else will have to be tried. This is one of the oldest PMS therapies and dates from the discovery that B6 is involved in the production of serotonin and dopamine, two of the ‘happy’ chemicals in the brain.The current therapy is 100 mg a day taken by mouth. The treatment is taken for the whole month, not just when you are likely to be premenstrual.But the evidence for vitamin B6′s efficacy is shaky. An analysis of 12 clinical trials of vitamin B6 found three with positive results, five with ambiguous results and four with negative results. Dutch researchers who analysed the B6 trials said: ‘At the moment there is no evidence that vitamin B6 is efficacious in the treatment of patients with PMS’.Despite this, some women do seem to improve when they are taking vitamin B6 and for this reason many doctors are prepared to give it a try.High doses of vitamin B6 are known to cause nerve damage resulting in symptoms like pins and needles, muscle weakness and even eye damage. The general consensus is that 100 mg a day is unlikely to cause problems and it is well worth sticking to that dose if you have been prescribed this medicine.*42\120\4*