Exogenous GH vs Endogenous Stimulation

The two strategies for raising growth hormone activity differ in where control sits. Injected recombinant growth hormone bypasses the axis and imposes a concentration curve set by the dose, indifferent to somatostatin tone, time of day or feedback. A secretagogue, whether a GHRH analogue at the GHRH receptor or a ghrelin mimetic at GHS-R1a, acts upstream on the somatotroph, so output is bounded by pituitary reserve and IGF-1 negative feedback, and it retains a pulsatile shape.

The regulatory asymmetry is large. Recombinant somatropin has been an approved drug since the mid-1980s, when it replaced cadaveric pituitary extract that had transmitted Creutzfeldt-Jakob disease. On the secretagogue side, tesamorelin is approved for HIV-associated excess visceral fat, macimorelin only as a diagnostic agent, and anamorelin holds a national approval in Japan. Everything else in the class, including the widely traded releasing peptides, is unapproved.

The practical consequence of the feedback ceiling is that secretagogues raise IGF-1 modestly and self-limit, while exogenous growth hormone can be pushed to any concentration and suppresses endogenous secretion while it is given. That difference changes the shape of the risk, but the dose-related class effects, fluid retention, arthralgia and reduced insulin sensitivity, appear with secretagogues too once IGF-1 rises meaningfully.

Two conclusions get drawn that the pharmacology does not support. The first is that a physiological release pattern is therefore safe, when what has been shown is a lower ceiling rather than an absence of harm. The second is the mirror error, assuming a secretagogue can substitute for replacement in organic deficiency; if the somatotrophs have been removed or irradiated there is nothing upstream to stimulate, and the class fails entirely.