TRT cessation does not inherently cause men to have suppressed hormone levels after. With precautions and extra steps like HCG to maintain leydig cell/testicular function, preventing atrophy, one may safeguard against that risk.
Coming off TRT, yes you will have lower levels as your HPTA has been suppressed by exogenous hormones. One may speed up this recovery using "PCT" (post cycle therapy), which involves taking a SERM (selective estrogen receptor modulator, e.g. enclomiphene) to resensitize and restart your HPTA. However this is not always necessary, and if one takes a look at the HARLEM study, most users return to their baseline levels within a year of going cold turkey.
In the cases of true permanently lowered levels of hormones, I believe the two most common reasons are: using other AAS besides testosterone (1) and lifestyle or health factors that correlate with the need to be on TRT (2).
With 1, this can be seen in users of decadurabolin (deca), which notoriously has hormone receptor active metabolites that last around for atleast a year, continuously suppressing the system. Or trenbolone (tren/cattle bulking hormone) which is inherently neurally and endocrinically otherwise toxic.
With 2, you hop on TRT because there is some reason your hormones are not at healthy levels. Whatever the reason is, it is still there, and once you've stopped bandaiding the issue its effects resurface.
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I have also used many GLP-1s (semaglutide, tirzepatide, and retatrutide). No there is no off-ramp, but the only effects I've noticed are a return to my baseline of appetite, and neurological state.
N.B. GLP-1s are good for impulse and behavioral disorders like ADHD, which it did help. However, I have decided to not take it due to the negative effects on personality and reward seeking behavior.
They are neuro-active in the brain, and their effects I've decided are not worth it.