T Nation

Estrogen Rebound Mechanism

Hi everybody!

Can someone explain how estrogen rebound works? I just don’t get couple of things.

William Llewellyn in his article on post cycle recovery wrote:

“…post cycle there is not an elevated level of estrogen for anti-estrogens to block, as testosterone (now suppressed) is a major substrate used for the synthesis of estrogens in men. Serum estrogen levels will actually be lower here as a result, not higher.”


“Any estrogen rebound that occurs post-cycle likewise happens concurrently with a rebound in testosterone levels, not prior to it (note there is an imbalance in the ratio post cycle, but this is another topic altogether).”

He doesn’t mention here why T/E2 imbalance occurs after cycle and I can’t find decent explanation anywhere.

As I understand it, when exogenous T enters system, E2 raises to catch up with T/E2 ratio caused by aromatization of overwhelming amounts of T.

After cycle there’s no T left (both exogenous and endogenous), so E2 levels are low (William writes about it).

But why after that balance is screwed up? Is this a result of increased production of aromatize or its upregulation? Assuming that 80-85% of estrogen is created by aromatization throughout a body - seems it plays the major role here.

The cycle can be quite short (3-8 weeks, for instance), but why the effect is so long-lasting?

Delayed gyno can appear after months and T/E2 balance may not be restored for a long time even if LH, FSH and T production came to normal.

Can someone shed the light on that or point me elsewhere for info? I think I’m going through “rebound” right now and got very interested in how that works.