After five years of trying to figure this out, I finally discovered that 400 mg of vitamin B6 in the form of P5P prevents the debilitating headaches that both vitamin D3 and 5-HTP supplements cause me. I took this amount for a few weeks, until it started to make me queasy. Then I lowered the dose. I’ve been taking about 100 mg of P5P a day for several weeks now.
Some sources say that only a portion of your B6 supplement intake needs to be in the form of P5P in order to take advantage of P5P’s bioactive superpowers, but this doesn’t seem to work for me. It has to be 100% P5P.
Regular old boring vitamin B6 unmistakably worked for me years ago, when I used rather modest amounts of it to get rid of carpal tunnel pain, but eventually it started giving me headaches and I began avoiding it. I’m guessing my recent need for such large doses of P5P was due to a major deficiency of it built up over the years by, among other things, taking very big doses of the amino acid l-glutamine (and later D3) without it. But that’s a story for another time.
I’ve run across the figure that 1 mg of P5P is equal in effectiveness to 50 mg of vitamin B6 (I’ve also seen 3 mg and 30 mg), but I don’t think this is helpful or appropriate. For me it seems to be like comparing apples and bullet trains.
As I’ve mentioned here before several times, you’ll see warnings everywhere that too much vitamin B6 causes nerve damage, when in fact these symptoms are often induced vitamin B12 deficiency symptoms — you’re rarely deficient in only one vitamin B, and they all interconnect. Apparently P5P doesn’t mess with B12 quite so badly.
FYI I find a lot of info about P5P on autism sites and forums.