It could not have been the cause of any of it, given the normal levels and the Clomid use. So much for the estrogen-only theory of inhibition that has been claimed by other writers. DHT, which does not aromatize, has been extensively shown to cause inhibition of testosterone production. Androgen alone, then, is sufficient to cause inhibition. In Jim s case, androgen use was moderately heavy, and androgen alone would seem the cause of the inhibition.
Progesterone is another hormone that can cause inhibition, when used long-term.
Paradoxically, in the short term it can be stimulatory. Other relevant factors include beta agonists, opiates, melatonin, prolactin, and probably other compounds. To understand inhibition of testosterone production, we need to know first how it is produced and how production is controlled. The broad general picture is that the hypothalamus receives a variety of inputs, for example, levels of various hormones, and decides whether or not more sex hormones should be produced. If the inputs are high, for example, high estrogen or high androgen or both, then it decides that little or no sex hormones should now be produced, but if all inputs are low, then it may decide that more sex hormones should be produced.