Ibutamoren vs Anamorelin

Both are orally active, non-peptide ghrelin-receptor agonists. Anamorelin completed phase 3 trials in cancer-related weight loss (ROMANA) and is approved in Japan; ibutamoren (MK-677) was studied for GH and IGF-1 elevation in older adults but never approved.

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Ibutamoren

An orally active, non-peptide growth-hormone secretagogue that mimics ghrelin at the GHS-R1a receptor.

BEST STUDIED FOR

GH secretagogues

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Anamorelin

An orally active, non-peptide ghrelin-receptor agonist approved in Japan for cancer cachexia — the best-trialled molecule in the secretagogue class.

BEST STUDIED FOR

GH secretagogues

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SIDE BY SIDE

	Ibutamoren	Anamorelin
The key difference	Oral, long-acting; studied for GH/IGF-1 in ageing	Oral; approved in Japan for cancer cachexia
Class	GH secretagogues	GH secretagogues
Mechanism	MK-677 is a small molecule (not a peptide) that activates the ghrelin receptor, producing sustained increases in GH and IGF-1.	Anamorelin binds GHS-R1a, increasing appetite signalling and GH/IGF-1 release, studied as a way to counter the muscle and weight loss of cancer anorexia-cachexia.
Status	Studied in clinical trials from the 1990s (catabolism, ageing, frailty); never approved. Widely sold as a "research chemical" and banned in sport.	Approved in Japan (2021) for cancer cachexia in several tumour types; two phase 3 trials (ROMANA 1 and 2) are the core dataset.
Reported safety signals	Reported effects include oedema, increased appetite and muscle pain; a 2025 case report described hepatotoxicity, and a 2024 case linked an adulterated performance supplement to gynaecomastia.	The phase 3 programme reported it was generally well tolerated; hyperglycaemia and other events were monitored. Meta-analyses summarise effects on body weight and lean mass.
A key study	A randomised, placebo-controlled crossover study measured MK-677’s effect on diet-induced negative nitrogen balance in healthy volunteers. (J Clin Endocrinol Metab 1998, PMID 9467534)	Two phase 3 trials measured anamorelin’s effect on lean body mass and other cachexia outcomes in advanced NSCLC. (Lancet Oncol 2016, PMID 26906526)

WHEN TO RESEARCH WHICH

Anamorelin is the better-documented compound for cachexia and lean-mass endpoints; ibutamoren for long-acting GH/IGF-1 elevation models. Both are discussed here strictly as research compounds; nothing on this page is medical advice or a dosing guide.

REFERENCES (PUBMED)

[Ibutamoren] MK-677, an orally active growth hormone secretagogue, reverses diet-induced catabolism — J Clin Endocrinol Metab 1998. PMID 9467534
[Ibutamoren] Repeat administration of the GH secretagogue MK-0677 increases and maintains elevated IGF-I levels in beagles — J Endocrinol 1997. PMID 9071975
[Ibutamoren] Hepatotoxicity induced by MK-677 — BMJ Case Rep 2025. PMID 40675653
[Anamorelin] Anamorelin in patients with non-small-cell lung cancer and cachexia (ROMANA 1 and ROMANA 2): results from two randomised, double-blind, phase 3 trials — Lancet Oncol 2016. PMID 26906526
[Anamorelin] Anamorelin for cancer anorexia-cachexia syndrome: a systematic review and meta-analysis — Support Care Cancer 2017. PMID 28074289
[Anamorelin] Anamorelin in Japanese patients with cancer cachexia: an update — Curr Opin Support Palliat Care 2023. PMID 37389636

FREQUENTLY ASKED

What is the difference between Ibutamoren and Anamorelin?

What is the regulatory status of Ibutamoren and Anamorelin?

Ibutamoren: Studied in clinical trials from the 1990s (catabolism, ageing, frailty); never approved. Widely sold as a "research chemical" and banned in sport. Anamorelin: Approved in Japan (2021) for cancer cachexia in several tumour types; two phase 3 trials (ROMANA 1 and 2) are the core dataset.

What safety signals have been reported?

Ibutamoren: Reported effects include oedema, increased appetite and muscle pain; a 2025 case report described hepatotoxicity, and a 2024 case linked an adulterated performance supplement to gynaecomastia. Anamorelin: The phase 3 programme reported it was generally well tolerated; hyperglycaemia and other events were monitored. Meta-analyses summarise effects on body weight and lean mass.

Which studies is this comparison based on?

For Ibutamoren: “MK-677, an orally active growth hormone secretagogue, reverses diet-induced catabolism” (PMID 9467534); “Repeat administration of the GH secretagogue MK-0677 increases and maintains elevated IGF-I levels in beagles” (PMID 9071975); “Hepatotoxicity induced by MK-677” (PMID 40675653). For Anamorelin: “Anamorelin in patients with non-small-cell lung cancer and cachexia (ROMANA 1 and ROMANA 2): results from two randomised, double-blind, phase 3 trials” (PMID 26906526); “Anamorelin for cancer anorexia-cachexia syndrome: a systematic review and meta-analysis” (PMID 28074289); “Anamorelin in Japanese patients with cancer cachexia: an update” (PMID 37389636).