This is an answer to a PM that I got from a younger guy that seems like it may be helpful. Sorry if its too redundant, but it seems like its perrenially misunderstood:

"Clomid is for PCT. Roids, including prohormones, shut down your nuts' production of testosterone because your system senses that there's enough test (or other steroids/prohormones that activate the same receptors as test) in your system, so your system stops producing it so you don't get above normal levels (Clomiphene is the chemical in it, so its the generic name by which it will be sold unless its the actual original brand name. Its like Tylenol = acetaminophen, right?)

Clomid was developed as a fertility drug for women who couldn't get pregnant. They discovered that it also stimulates the nuts to increase production of testosterone in men. Believe it or not, male porn actors take it to increase their load when the cum on female porn stars. Trip, huh?

When we stop a cycle, we no longer have the test (or other similar things, which other steroids are), and our own production of natural test is still shut down, so all the muscle we've built on a cycle can VANISH ion a few weeks!
That's fucked!

Exemestane (which is the generic name for Aromasin), is an aromatase inhibitor. Aromatase is and enzyme that converts a percentage of a male's testosterone into estrogen. This is a normal and healthy process; we need a little estrogen. But if we greatly increase our testosterone levels, (or any other "aromatizable" steroid), then the same percentage is converted into estrogen, but since its a percentage of a much bigger overall number, we end up with too much estrogen which leads to bad side effects. Taking a little aromasin when on any cycle which includes test or other aromatizing steroids will keep the enzyme--aromatase--from converting as much test into estrogen and keep estogenic side effects at bay.

Its also important to remember that, just as too much estrogen is not good for us, nor is too little. That's why I say that its good to take a little exemestane, but this is totally related to the amount of test, etc., that one is using; and, the propensity of the specific man's physiology for converting test into estrogen, and its ability to cause side effects to a degree that is harmful. So, a little exemestane (or other aromatase inhibitor, or "ai") for me, may be a lot for you, and vice versa. I know that I took too much for awhile and it made me feel like hell.

The only way to know for sure is to go by standard recommendations which you can easily find in forum posts, and see how your body reacts. Then, ultimately, get blood work done that includes sensitive estrogen testing."