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The HPG Axis vs the GH Axis: Why It Matters
Your testosterone is governed by the hypothalamic-pituitary-gonadal (HPG) axis. The hypothalamus releases gonadotropin-releasing hormone (GnRH) in pulses. GnRH tells the pituitary to release luteinizing hormone (LH), and LH tells the Leydig cells in the testes
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- Your testosterone is governed by the hypothalamic-pituitary-gonadal (HPG) axis. The hypothalamus releases gonadotropin-releasing hormone (GnRH) in pulses. GnRH tells the pituitary to release luteinizing hormone (LH), and LH tells the Leydig cells in the testes to make testosterone.
- Growth hormone runs on a separate circuit. GH-releasing peptides like sermorelin and CJC-1295 act on the pituitary to release growth hormone, which raises IGF-1. That pathway changes fat and muscle. It does not pull the LH lever that drives testosterone.
- Think of it like two breaker switches on the same panel. One switch powers the testosterone circuit (GnRH to LH to Leydig cells). The other powers growth hormone. Flipping the GH switch lights up body composition, but the testosterone circuit stays exactly where you left it. A peptide raises your testosterone only if it acts on the HPG breaker.