Sermorelin vs Ipamorelin: GHRH analog vs GHRP for IGF-1 elevation

Sermorelin and ipamorelin both elevate IGF-1 by stimulating the pituitary to produce more growth hormone, but they act on different receptors and through different mechanisms.

Sermorelin is a GHRH analog: the synthetic 29-amino-acid N-terminal fragment of endogenous GHRH. It binds the GHRH receptor on somatotroph cells, priming them to release GH. It was the original compounded GH secretagogue, FDA-approved for growth hormone deficiency diagnosis (Geref) before being withdrawn and later reprised by compounding pharmacies. Its main limitation is the 6.5% subclinical hypothyroidism incidence documented in its prescribing information, driven by GH-mediated acceleration of T4-to-T3 conversion.

Ipamorelin is a GHRP: it activates the ghrelin receptor (GHS-R1a) to trigger GH release. Unlike sermorelin, which primes the somatotroph, ipamorelin directly fires the GH release mechanism. Its selectivity is exceptional: it does not stimulate cortisol, ACTH, or prolactin even at doses far exceeding the effective GH dose (Raun et al., 1998, PMID 9849822). It has no documented thyroid effect.

When stacked together, sermorelin (GHRH primer) and ipamorelin (GHRP trigger) produce synergistic GH pulses through dual receptor activation. In practice, CJC-1295 no-DAC has largely replaced sermorelin in bodybuilding stacks due to better stability, but sermorelin remains the more available GHRH analog in compounding pharmacy contexts.

Receptor class: Sermorelin targets the GHRH receptor. Ipamorelin targets GHS-R1a (ghrelin receptor). This is the fundamental mechanistic distinction.

Thyroid risk: Sermorelin carries a 6.5% subclinical hypothyroidism risk per its FDA prescribing information (Geref PI), attributed to GH-mediated D2 deiodinase upregulation and T4-to-T3 conversion acceleration. Porretti et al. (2002, PMID 11994338) documented that GH treatment can unmask subclinical hypothyroidism. Ipamorelin has no documented thyroid effect, which is a meaningful clinical advantage for users with borderline thyroid function.

Cortisol and prolactin: Ipamorelin does not affect cortisol or prolactin at any dose tested. Sermorelin, being a GHRH analog, does not have the same cortisol/prolactin concern as GHRPs like GHRP-2 or GHRP-6. However, ipamorelin's selectivity data are more thoroughly documented.

Availability and form: Sermorelin is the most commonly compounded GHRH analog in prescription markets (Australia, USA). CJC-1295 no-DAC is more common in the grey market. Both are injectable.

Evidence base: Sermorelin has historical FDA prescription data and its prescribing information provides valuable safety incidence data. Ipamorelin has Phase I PK/PD data (Raun et al., 1998; Gobburu et al., 1999) but no long-term RCT.

Solo compound value: Ipamorelin functions well as a standalone GH secretagogue because it directly triggers GH release. Sermorelin alone relies on amplifying the endogenous GHRP signal, producing a more modest GH response when used without a concurrent GHRP.

Choose sermorelin when:

• You are accessing GH peptides through a compounding pharmacy (sermorelin is more commonly prescribed)
• You want a GHRH analog to pair with ipamorelin and the compounding option favours sermorelin over CJC-1295
• You have baseline thyroid function testing complete and no borderline thyroid concerns
• You are working with a physician who is familiar with sermorelin protocols

Choose ipamorelin when:

• You want the cleanest hormonal selectivity profile (no cortisol, prolactin, or thyroid effects)
• You have any borderline thyroid markers or Hashimoto's history (sermorelin's thyroid risk is a contraindication concern)
• You are cutting (ipamorelin has no appetite effect; sermorelin also has no direct appetite effect, but check your context)
• You want a solo compound without needing a concurrent GHRH analog for meaningful results

Stack both when:

• You want to maximise pulsatile GH/IGF-1 elevation by activating both the GHRH receptor and GHS-R1a simultaneously
• Protocol: 100-200 mcg sermorelin + 200-300 mcg ipamorelin per injection, pre-bed fasted
• Monitor TSH and free T4 at baseline and at 8 weeks if using sermorelin