From Kaiser Permanent about C\L and Vitamin B6 and B3 - wa.kaiserpermanente.org/kba...
B6 - "Test tube, animal, and preliminary human studies suggest that carbidopa may cause depletion of vitamin B6. However, the use of carbidopa with levodopa reduces the vitamin B6-depleting effects of levodopa. More research is needed to determine whether vitamin B6 supplementation is advisable when taking carbidopa."
B3 - "A study in animals has found that carbidopa inhibits an enzyme involved in the synthesis of niacin in the body. In addition, there is evidence that niacin synthesis is decreased in people taking carbidopa and other drugs in its class, raising the concern that people taking these drugs could be at risk of niacin deficiency, even if not frankly deficient. Further studies will be required determine if niacin supplementation is appropriate in people taking carbidopa."
There doesn't seem to be evidence that show benefits to taking B6. I do think that lack of b6 indirectly affects PWP and PSP patients. Google b6 deficiency.
Thank you.