The growth hormone peptide category is large, and the compounds in it work through different mechanisms despite being grouped together. This thread is an overview of what compounds are in this class, how they relate to each other, and what researchers in this space are studying.
The fundamental distinction: secretagogues, not GH itself.
None of the compounds in this category are growth hormone. They are growth hormone secretagogues — compounds that stimulate the pituitary to release endogenous GH. This is mechanistically and pharmacologically distinct from administering recombinant human growth hormone (rhGH) directly. The secretagogues work upstream and the resulting GH release is pulsatile and regulated by the body's own feedback systems, while exogenous rhGH bypasses that regulation entirely.
The two mechanism families.
GHRH analogs. These compounds mimic growth hormone-releasing hormone, the hypothalamic peptide that signals the pituitary to release GH. CJC-1295, sermorelin, and tesamorelin fall in this family. They activate the GHRH receptor on pituitary somatotrophs.
Ghrelin mimetics (GH secretagogue receptor agonists). These compounds activate the GHSR-1a receptor — the same receptor that endogenous ghrelin binds. The GHRPs (GHRP-2, GHRP-6, hexarelin), ipamorelin, and MK-677 (ibutamoren) all work through this pathway. They produce GH release through a different signaling cascade than the GHRH analogs.
The two pathways are synergistic — combining a GHRH analog with a ghrelin mimetic produces greater GH release than either alone. This is the pharmacological basis for the CJC-1295 + ipamorelin combination that dominates this category's research literature.
The compounds researchers are studying.
CJC-1295 (with and without DAC). A modified GHRH analog. The "with DAC" version (Drug Affinity Complex) adds a binding moiety that allows reversible albumin binding, extending the half-life from minutes to several days. The "without DAC" version (also called Mod GRF 1-29) is the short-acting version. The half-life difference produces dramatically different pharmacological profiles — one supports continuous elevation of baseline GH, the other supports sharp pulsatile spikes. There is a dedicated thread comparing the two in this category.
Ipamorelin. A selective ghrelin mimetic. Considered the "cleanest" GHRP because it produces less of the cortisol and prolactin elevation seen with GHRP-2 and GHRP-6, and minimal hunger stimulation. This selectivity is why ipamorelin became the dominant ghrelin mimetic in research protocols. Half-life is approximately 2 hours.
GHRP-2 and GHRP-6. Older ghrelin mimetics. GHRP-6 produces noticeable hunger as a side effect (relevant for some research applications, problematic for others). GHRP-2 has stronger GH release than ipamorelin but with more cortisol and prolactin elevation. Both are still used in research but ipamorelin has largely displaced them for general protocols.
Hexarelin. A more potent ghrelin mimetic with stronger receptor affinity than the GHRPs but also more pronounced desensitization with extended use.
MK-677 (ibutamoren). Orally bioavailable ghrelin mimetic. The only compound in this category that does not require injection. Produces sustained GH and IGF-1 elevation throughout the day rather than discrete pulses. Also produces significant hunger increase and sometimes water retention. Research applications and protocols differ substantially from injectable secretagogues.
Tesamorelin. A modified GHRH analog approved for HIV-associated lipodystrophy. The most extensively studied GHRH analog from a clinical research standpoint. Has shown specific effects on visceral adipose tissue beyond what would be expected from total fat loss alone.
What is being researched.
Body composition (fat loss and lean mass), recovery from training and injury, sleep architecture (GH peptides often improve deep sleep stages), IGF-1 effects, age-related GH decline, cognitive endpoints, and the safety profile of long-term secretagogue use. The research base is older and more mature than the GLP-1 literature but less active right now in terms of new clinical trials.
The protocol design implications.
Because endogenous GH is naturally released in pulses (primarily during deep sleep), the secretagogue pulse pattern matters. Multiple smaller doses across the day mimic the natural pulsatility better than single large doses. This is why typical research protocols involve 2-3 daily injections rather than once-daily. The Mechanism + Half-Life thread covers this in detail.
Where to go next.
The deeper threads in this category cover specific topics. The CJC-1295 with-DAC versus without-DAC thread explains the half-life decision. The ipamorelin "cleanest GHRP" thread explains the selectivity advantage. The MK-677 thread covers the oral secretagogue specifically. The tesamorelin versus CJC-1295 thread compares the two GHRH analogs. The blood work thread covers what to test and when. The Mechanism + Half-Life thread in this Research Library covers the pharmacology in depth. The Quality + COA thread covers vendor evaluation. The Red Flags thread covers the specific scam patterns in this market.
