5-HTP is the precursor to serotonin. Some take L-Tryptophan which is made into 5-HTP when the brain needs it. It is safer to take L-Tryptophan because the body regulated how much is converted to 5-HTP then serotonin.

Some with PCS become serotonin deficient which leads to anxiety and depression. B-12 and the rest of the vitamins can help the brain tolerate stress and be less anxious and less depressed.