P-5-P is a B vitamin. It is normally known as Vitamin B-6, but the P-5-P version is "predigested" so that it places no stress on your liver. Regular Vitamin B-6 has to be converted into a usable form by the liver. And the last thing any of us here need is to stress our liver!
You mention your B-complex formula. Some formulas have the B-6 in the form of P-5-P, but probably most don't.