Ipamorelin vs Macimorelin
The distinction that mattersMacimorelin is an oral ghrelin-receptor agonist that is FDA-approved, and that approval is sometimes cited as proof the class is legitimate therapy. It is approved as a single-dose diagnostic test for adult growth hormone deficiency — the point is to provoke one GH pulse and measure it, not to treat anything. An approval for a one-off diagnostic says nothing about repeated use of ipamorelin for recovery or body composition.
These are not equivalent in evidence Macimorelin is rated 5/5 and Ipamorelin is rated 2/5 — a gap of 3 levels on our scale. Similar marketing does not mean similar proof.
| Ipamorelin Research Use Only | Macimorelin FDA Approved | |
|---|---|---|
| Evidence rating |
2/5 Limited
Evidence rating 2 out of 5: Limited
|
5/5 Very strong
Evidence rating 5 out of 5: Very strong
|
| Regulatory status | Investigational only, and not approved anywhere. Two phase 2 trials in postoperative recovery of gastrointestinal function were completed without demonstrating benefit, after which development was abandoned. Widely supplied through wellness clinics and research-chemical sellers, which is not the same as being lawfully available. | FDA-approved (2017) and EMA-approved for the diagnosis of adult growth hormone deficiency. |
| Category | Growth Hormone Axis | Growth Hormone Axis |
| Drug class | Selective ghrelin receptor (GHS-R1a) agonist — pentapeptide | Orally active ghrelin receptor agonist — peptidomimetic |
| Route | Subcutaneous (research) | Oral, single diagnostic dose |
| Half-life | ~2 hours | ~4 hours |
| Sequence length | 5 residues | 3 residues |
| Molecular weight | 711.9 Da | 474.6 Da |
| Studied in | Healthy-volunteer intravenous pharmacokinetics and GH response (1999); two completed phase 2 trials of postoperative recovery of gastrointestinal function, neither positive, after which development stopped; rodent studies of gut motility, longitudinal bone growth and bone mineral content. | Pivotal randomized crossover trial against the insulin tolerance test, the previous reference standard. |
| Who should avoid it |
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| Legal status | Not approved by the FDA, the EMA or any comparable regulator for any indication, and not eligible for lawful pharmacy compounding in the United States. Selling it for human use is unlawful. “Research use only” or “not for human consumption” labelling is a seller’s disclaimer about intended use, not a regulatory category, and confers nothing on the buyer. The compounding position is disputed and moving; the dated record is on this page. | Prescription diagnostic agent, administered under medical supervision. |
Benefits — Ipamorelin
- Selective GH release
Clean pharmacology: GH rises without the cortisol and prolactin spikes seen with hexarelin or GHRP-6.
- Minimal appetite stimulation
Unlike GHRP-6, it does not produce the intense hunger that makes those peptides impractical.
- Good short-term tolerability
Trial safety data in the ileus program were reassuring over short exposures.
- Synergy with GHRH analogs
The two mechanisms combine to produce a larger pulse than either alone.
- A measurable, reproducible GH pulse in healthy humans
A 1999 dose-escalation study in healthy male volunteers (eight men at each of five ascending intravenous infusion rates) found dose-proportional pharmacokinetics, a terminal half-life near two hours, and a single episode of GH release peaking around 40 minutes and decaying to negligible concentrations at every exposure tested. This is the clearest human evidence the compound does what it says — and it is evidence about a hormone measurement, not about anything a person would notice.
Benefits — Macimorelin
- Replaces a genuinely dangerous test
The insulin tolerance test requires deliberately inducing hypoglycemia under supervision and is contraindicated in cardiac disease and epilepsy. Macimorelin achieves comparable diagnostic accuracy with an oral solution.
- High diagnostic agreement
The pivotal trial showed sensitivity and specificity closely matching the insulin tolerance test.
- Oral and outpatient
No infusion, no induced hypoglycemia, no intensive monitoring.
- Proves oral GH secretagogues are feasible
A useful reference point when assessing unapproved oral secretagogue claims.
Risks & cons — Ipamorelin
- No proven clinical benefit
The trials that were run targeted gut motility and were discontinued. Body-composition and recovery claims are untested.
- Unapproved and unregulated
Available only through compounding or grey-market suppliers, with corresponding quality uncertainty.
- Glucose and insulin effects
Raising the GH axis can worsen insulin sensitivity over time.
- Receptor desensitisation
Continuous ghrelin-receptor stimulation blunts the response; effects diminish with sustained use.
- Head/injection-site reactions
Headache, flushing and local reactions are reported.
Risks & cons — Macimorelin
- Diagnostic use only
It is not a treatment. There is no evidence base for repeated dosing, and no approval for therapeutic use.
- QT interval prolongation
The main safety concern; concurrent QT-prolonging drugs must be stopped before testing.
- Dysgeusia
A distorted or metallic taste is the most common adverse effect.
- False results with interfering drugs
Strong CYP3A4 inducers and recent GH therapy can invalidate the test.
- Fatigue and headache
Reported after the single dose.
A comparison is not a recommendation. Neither column is being suggested for you. Which — if either — is appropriate depends on your diagnosis, history and medications, and that is a conversation for a qualified clinician.