Cortisol levels rise dramatically during a cycle, the body's way of trying to maintain a homeostatic mechanism over the new muscle growth; this is why the best gains will usually be experienced from weeks 2 until weeks 5-6. After weeks 5-6 gains slow to a crawl, because they are mostly due to cortisol antagonism by androgens (anti-catabolic mechanism) rather than conventional anabolism. Cortisol levels start low, and then rise slowly to meet higher androgen levels. This can be mitigated by either increasing the dosage, cycling off, or using something that blocks cortisol (real drugs, which is definitely NOT recommended). Food can also keep cortisol levels lower, as insulin blunts cortisol; this is why dieting or cutting calories post-cycle is a bad idea.
When a person stops whatever exogenous androgen they are on their androgen levels will plunge and cortisol levels will remain elevated during PCT. As long as this ratio is out-of-whack, they will be in a catabolic state and losing muscle mass. DHEA can help will this (as well as cissus and B6) because when cortisol levels are high DHEA can compete with the same receptor sites. It may not necessarily be the most anabolic thing in the world, but it is not catabolic, and by competing with cortisol, you can keep at least some of it from binding while androgen levels return to normal. Cytokine levels also rise sharply during a cycle along with cortisol levels, and cytokines are VERY catabolic. DHEA, B6, and cissus each lower cytokine levels, and can be very helpful in this regard. Lot of different inter-related things go into PCT, not just testosterone and estrogen.
~Rosie
Team APPNUT