There are no quick fixes
Hormones and neurotransmitter stimulation is not the answer. In fact these things actually have something in common--they dramatically increase methionine synthase activity. Problem is, if you believe Rich and the research of others, methionine synthase activity is impaired You have to get to the root of the problem. What inhibits methionine synthase activity is neurotoxins and oxidative stress. This would include lead, mercury/thimerosol, alcohol, excessive energy output, viruses, chronic infections, xenobiotics. Personally, I've had success with radical dietary changes and gut modification followed by pursuing a combination of methylation protocols espoused by Rich and Freddd. I have nearly fixed my gastrointestinal issues and it eventually became clear that these played a very significant causal role in the brain fog. The immune response created by the intestinal dybiosis was also strongly associated with the fatigue. I believe my improvement was in large part created by the crap in my body (mostly anaerobic bacteria & yeast) that I eliminated, and I think everyone who has any digestive issues should pursue the diet and gut modification changes, and most will benefit from methylation support, which has a synergistic effect. Adding methyl donors should be done cautiously and slowly; it has proven to be quite challenging at times.
In short, you have to take all the clues you have, and go after what you know exists as a problem, but I think getting the body to ramp up production of glutathione provides many benefits. An endogenous solution is always going to be more effective than an exogeonous solution.