Ipamorelin
Ipamorelin (Selective GHRP)
Ipamorelin is a pentapeptide GHRP that selectively stimulates GH release via ghrelin receptor (GHSR-1a) activation with high receptor selectivity and minimal off-target hormonal effects. It is the most commonly used GHRP in research protocols due to its clean hormonal profile — producing robust GH pulses without meaningful increases in cortisol, prolactin, or ACTH.
Mechanism of Action
Ipamorelin activates growth hormone secretagogue receptors (GHSR-1a) in the pituitary, triggering pulsatile GH release. Unlike first-generation GHRPs (GHRP-6, GHRP-2), ipamorelin's selectivity for GHSR-1a is high enough to produce GH stimulation without triggering the adrenocortical or lactotropic pathways that cause cortisol and prolactin release.
When co-administered with a GHRH analogue (CJC-1295, sermorelin), ipamorelin acts synergistically — the GHRH analogue amplifies the GH synthesis capacity of the somatotroph cells while ipamorelin triggers the release. This combination produces GH pulses several-fold larger than either compound alone.
Ipamorelin's short half-life (~2 hours) means its effect is concentrated into a discrete GH pulse that mimics physiological pulsatility — maintaining the natural rhythmic GH pattern rather than creating sustained supraphysiological GH levels.
Research Evidence
Ipamorelin was among the first highly selective GHRPs to enter research. Phase 1 trials confirmed its clean hormonal profile. It remains a reference GHRP in comparative studies and is widely used as the GHRP component in GH optimisation research protocols.
Ipamorelin: A Highly Selective Growth Hormone Secretagogue
Ipamorelin produced robust, dose-dependent GH release in rats comparable to GHRP-6, but with statistically insignificant changes in prolactin, cortisol, and ACTH — confirming its selectivity advantage over earlier GHRPs.
Typical Research Protocol
Most commonly combined with CJC-1295 (without DAC) in a 1:1 ratio by mcg, administered together at the same time.
Safety Profile
Reported Side Effects
- Water retention (mild)
- Tingling/numbness (extremities)
- Headache (transient)
- Injection site redness
- Increased hunger (less than GHRP-6)
Contraindications
- Active malignancy
- Uncontrolled diabetes
- Pregnancy
- History of GH-sensitive tumours
Common Research Stacks
Frequently Asked Questions
Why is Ipamorelin preferred over GHRP-2 or GHRP-6?
Ipamorelin's receptor selectivity means it produces a clean GH pulse without the cortisol elevation (seen with GHRP-2 at higher doses) or pronounced appetite stimulation (seen with GHRP-6 via ghrelin). For most research protocols targeting body composition and recovery, this cleaner hormonal response is preferable.
Does Ipamorelin need to be taken fasted?
A fasted state maximises GH pulse amplitude because elevated insulin (post-meal) suppresses GH release via somatostatin. Waiting at least 2 hours after a meal — or dosing before bed — produces the largest responses. However, the difference between fasted and fed dosing is modest for Ipamorelin compared to GHRP-6.
How long should an Ipamorelin cycle last?
Standard research protocols run 8–12 weeks on followed by 4 weeks off. Longer continuous use risks receptor desensitisation and reduced GH pulse amplitude over time. Some protocols use 16 weeks on / 4 weeks off without significant desensitisation. Monitoring IGF-1 levels is the best way to track whether the protocol remains effective.
What results can be expected from Ipamorelin?
Common research observations across combined GH peptide protocols include: improved sleep quality and recovery (often the first noted effect), reduced body fat (particularly visceral fat over 8+ weeks), increased lean muscle tissue, improved skin texture, and elevated energy levels. Results emerge gradually — significant body composition changes typically require 12+ weeks.
What is the difference between Ipamorelin and GHRP-6?
GHRP-6 produces stronger GH pulses than Ipamorelin at comparable doses but causes significant appetite stimulation (via ghrelin activity) and can elevate cortisol and prolactin. Ipamorelin's superior selectivity for GHSR-1a produces a clean GH pulse with minimal appetite increase and no meaningful cortisol or prolactin effect — making it better suited to long-term protocols.
Key Research References
- Raun K et al. (1998). Ipamorelin, the first selective growth hormone secretagogue. Eur J Endocrinol.
- Johansen PB et al. (1999). Ipamorelin does not increase cortisol, ACTH or prolactin. Growth Horm IGF Res.
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