Phos/Serine was just prescribed for me a little over a week ago for my adrenal challenges - I don't notice anything yet for brain fog but I'll let you know. From what I understand it can take about a month or so to get some good affects, primarily for my brain fog and sleep issues.
I take it at bedtime to balance out cortisol during the night. The idea is to take my natural cortisol before noon and then balance it out at night with the PS. I will start taking 5 HTP along with the PS in about a week. If you don't have cortisol challenges you would not want to take this PS supplement at bedtime!
One good thing I've notice is that I get 2 extra hours sleep before I wake up - I use to wake up at 2, now it's 4. Hopefully it will soon be 6!!!