Macimorelin vs MK-677
How Macimorelin and MK-677 compare — what each is, how strong the human evidence is for each, doses reported in research, the key risks, and 2026 US legal status. No universal winner.
Macimorelin and MK-677 come up together when people are weighing similar options. Here's the honest side-by-side: what each is, how strong the human evidence is for each, the doses reported in research, the risks, and where each stands with the FDA as of 2026. There's no universal winner — scroll to the by-goal picks for which one fits which goal.
Macimorelin vs MK-677, point by point
Every dimension side by side — the honest differences, not a scoreboard.
| Dimension | Macimorelin | MK-677 |
|---|---|---|
| What it is | Oral peptidomimetic growth hormone secretagogue receptor agonist (ghrelin receptor agonist) | Non-peptide small molecule; orally active growth hormone secretagogue (ghrelin-receptor agonist) |
| Class / category | GH secretagogues | GH secretagogues |
| Evidence tier | Human RCT · Helped | Human RCT · Mixed |
| Studied / approved for | Diagnosis of adult growth hormone deficiency | Age-related decline in growth hormone; Muscle wasting / sarcopenia; Growth hormone deficiency (as LUM-201); Recovery after hip fracture |
| US regulatory status (2026) | fda approved (as of Jul 2026) — approved for Diagnosis of adult growth hormone deficiency | research use only (as of Jul 2026) |
| Doses reported in research | No established study doses | No established study doses |
| Registered trials (ClinicalTrials.gov) | No data | 8 |
| Banned in sport (WADA) | Yes — on the WADA prohibited list | Yes — on the WADA prohibited list |
| Key risks | Macimorelin is given once for a supervised diagnostic test, and its short-term adverse-event record is based on human studies. Unpleasant taste, dizziness, headache, fatigue, nausea, and hunger were reported. The main serious warning is QT prolongation, which can trigger a dangerous heart rhythm; interacting drugs can also distort the test result. Long-term carcinogenicity and fertility studies have not been conducted because Macrilen is not labeled for chronic use. | MK-677 has more human safety data than almost any compound sold on the research market, and that data is a mixed bag. It reliably causes water retention, a bump in appetite, and higher blood sugar with lower insulin sensitivity. A trial in frail elderly hip-fracture patients was stopped early after more heart-failure events in the MK-677 group — a warning that matters most for older or cardiovascular-risk users. It is not an approved medicine, and long-term use in healthy adults is unstudied. |
- Evidence tier: A tier reflects how human the evidence is, not a promise the compound works.
Macimorelin vs MK-677: the two molecules
The 2D chemical structures, straight from PubChem — a quick way to see how similar (or not) the two actually are.
Which one fits which goal?
There's no universal winner here — the honest answer depends on what you're after. These picks are framed by goal, and each says why.
If you want an FDA-approved, prescribable option
Leans toward Macimorelin
Macimorelin is FDA-approved (as of Jul 2026); MK-677 is research use only in the US, so it isn't available as an approved prescription.
References
- 1.MACRILEN (macimorelin) prescribing information
- 2.FDA approval record for macimorelin acetate
- 3.FDA Division Director Summary Review — NDA 205598
- 4.Garcia et al., 2018 — Macimorelin as a diagnostic test for adult GH deficiency (PMID 29860473)
- 5.Macimorelin — PubChem CID 9804938
- 6.Macimorelin — DrugBank DB13074