Ipamorelin, GHRP-6, and GHRP-2 are all members of the same family — ghrelin-receptor (GHS) agonists. They all pull the exact same lever: the ghrelin receptor, one of the two triggers for a growth-hormone pulse. So what separates them isn't *what* they do, it's *how cleanly* they do it.
In plain terms: same job, different amounts of extra noise.
One family, one lever
All three copy ghrelin — the "hunger hormone" — at the GHS receptor to make the pituitary release growth hormone. The family has a clear lineage: GHRP-6 came first (1984), and GHRP-2 and ipamorelin are later refinements aimed at cutting the side-effects.
| GHRP-6 | GHRP-2 | Ipamorelin | |
|---|---|---|---|
| Class | GHS agonist | GHS agonist | GHS agonist |
| Role in history | 1984 founder | Optimized successor | Selective refinement |
| Appetite (hunger) signal | Strong | Moderate | Minimal |
| Cortisol / prolactin nudge | Noticeable | Less | Minimal |
| Defining trait | Original | More potent, cleaner | Cleanest ("selective") |
The "cleanliness" story
This is the whole comparison, so it's worth walking through:
- GHRP-6 was the breakthrough — the first synthetic peptide shown to make the pituitary release growth hormone through this new switch1. But it's a bit *noisy*: it also stirs a strong hunger signal and nudges cortisol and prolactin.
- GHRP-2 (also called pralmorelin) was tuned for stronger, somewhat cleaner growth-hormone release, with less appetite stimulation than GHRP-6 — though it still isn't silent on the side-signals.
- Ipamorelin is the cleanest. Its founding 1998 study showed it released growth hormone about as strongly as GHRP-6 but without raising cortisol or ACTH2. That selectivity is its entire reason for existing (what is ipamorelin).
What the studies actually found
| Study | Model | Key result | Year |
|---|---|---|---|
| Bowers et al.1 | Rat + pituitary cells (GHRP-6) | Founded the class: first peptide to release growth hormone via the ghrelin switch, separate from GHRH | 1984 |
| Raun et al.2 | Rat, pig + cells (ipamorelin) | Matched GHRP-6's growth-hormone release but, unlike it, did not raise cortisol — the "selective" result | 1998 |
Note the model: this is preclinical evidence — animals and cells. It's a well-characterized difference in hormone profile, not a set of proven human outcomes.
Why this class sits opposite the GHRH analogs
All three are the ghrelin-receptor half of the growth-hormone picture. The GHRH analogs (sermorelin, CJC-1295, tesamorelin) are the other half, pulling the separate GHRH lever. That's exactly why ipamorelin is so often paired with CJC-1295 — two different levers, not two versions of one (CJC-1295 vs ipamorelin).
The honest bottom line
The selectivity ranking (GHRP-6 noisiest → ipamorelin cleanest) is a real, well-documented difference in hormone profile. But all three are research compounds with largely preclinical evidence, and all sit inside the FDA's ongoing 503A compounding review3. None is an approved general growth-hormone medicine. The full landscape is in growth-hormone secretagogues explained.