I am able to second what @dckuke says, also from experience and not as a medical person: I have been using P5P for going on three years, with no ill effects, most encouragingly, with no measurable worsening of my PN-induced problematic balance. The P5P was first prescribed for me by my neurologist in the form of a "medicinal food" called EB-N5. I now use a modified formulation, still with P5P, called EB-M8. –Ray (@ray666)