Axis Suppression

Axis suppression is negative feedback taken to its conclusion. The hypothalamus and pituitary sense the circulating product, not its source, so exogenous glucocorticoid or androgen reads as evidence that the gland is already working. Releasing hormone and trophic hormone output both fall, and the target gland loses the stimulus that maintains it. Suppression therefore has two stages with different recovery timescales: fast functional silencing, then slower structural atrophy.

Exogenous testosterone drives LH and FSH toward undetectable within weeks, and because intratesticular testosterone normally runs far above serum, losing LH drive removes the local androgen spermatogenesis depends on. WHO male contraception trials using injected androgen produced azoospermia or severe oligozoospermia in the large majority of participants, with sperm counts typically returning within several months, though with a long tail. On the adrenal side, supraphysiological glucocorticoid beyond about three weeks is the conventional point at which HPA suppression must be assumed.

Suppression is predictable, not idiosyncratic, so it belongs in the decision before treatment starts rather than in the adverse-event list afterwards. It is why abrupt glucocorticoid withdrawal risks adrenal crisis and needs a taper, and why fertility preservation belongs before testosterone therapy rather than during it.

The persistent misreading is that a normal hormone level on therapy means the axis is intact. It means only that the exogenous supply is adequate; the axis behind it may be silent, and only the trophic hormone reveals that. A second error assumes recovery follows a schedule: duration, dose, age and baseline function all shift it, the published data are largely observational, and the confident timelines circulating in grey-market post-cycle advice are not supported by controlled evidence.