Ibutamoren (MK-677)
Ibutamoren mesylate
Also known as: MK-677, ibutamoren, L-163,191, Nutrobal
This ingredient is classified as unclassified risk (GIRI score: 9.0/10).
Safety Profile
Known Safety Concerns
- Unapproved investigational drug — illegal as supplement everywhere
- FDA warning letters issued
- Increases IGF-1 — possible cancer growth promotion
- Insulin resistance and fluid retention documented
- WADA-prohibited — athletes sanctioned from supplement use
Contraindications
- Unapproved investigational drug — illegal as supplement everywhere
- FDA warning letters issued
Interactions
Information not yet available for this ingredient profile.
Evidence and Scientific Findings
Ingredient Overview
Ibutamoren is an unapproved investigational growth hormone secretagogue sold illegally as a supplement. It stimulates GH and IGF-1 release. No approved human use exists anywhere. The FDA has issued warning letters. It causes insulin resistance, increased appetite, fluid retention, and may promote cancer growth via IGF-1 pathway upregulation. WADA prohibits it. It is widely sold online under the name MK-677 despite being an unapproved drug.
Biological and Chemical Classification
- Scientific Name
- Ibutamoren mesylate
Mechanism of Action
Information not yet available for this ingredient profile.
Clinical Evidence of Effectiveness
Information not yet available for this ingredient profile.
Pharmacokinetics
Information not yet available for this ingredient profile.
Recommended Dosage
Information not yet available for this ingredient profile.
SETI — Scientific Evidence Transparency Index
Executive Summary — Ingredient Assessment
- 2 studies reviewed
- 0 high-quality studies (meta-analysis or RCT)
- Main clinical benefit observed: Banned Substance
- Evidence consistency: High consistency across studies (100%)
- Unapproved investigational drug — illegal as supplement everywhere
- FDA warning letters issued
- Increases IGF-1 — possible cancer growth promotion
- Insulin resistance and fluid retention documented
- WADA-prohibited — athletes sanctioned from supplement use
The available scientific evidence for Ibutamoren (MK-677) indicates notable safety signals that warrant caution. Use should be considered carefully and monitored, particularly in sensitive populations or alongside other medications.
Total SETI Score
High risk| Evidence quality | 2/40 |
| Evidence consistency | 20/20 |
| Safety signals | 16/20 |
| Study recency | 10/10 |
| Evidence transparency | 10/10 |
Evidence Summary
- 2 studies reviewed
- 0 high-quality studies (meta-analysis or systematic review)
- 0 studies identified benefits or no safety concern (GREEN)
- 2 studies reported limited or advisory safety evidence (YELLOW)
Evidence Policy
Only peer-reviewed scientific literature indexed in PubMed or comparable databases is included in this evaluation. Commercial websites, blogs, and marketing materials are excluded. All references include direct traceable links to source documents.
Last updated: 23 მარ 2026, 15:16
Evidence Distribution
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Observational / other LOW evidence YELLOWEquine metabolism of the growth hormone secretagogue MK-0677 in vitro and in urine and plasma following oral administration. ↗Cutler C et al.. Equine metabolism of the growth hormone secretagogue MK-0677 in vitro and in urine and plasma following oral administration.. Drug Test Anal. 2022. PMID:35302297.PMID 35302297 ↗Journal Drug Test AnalYear 2022Study type Observational / otherEvidence strength LOW evidencePubMed link https://pubmed.ncbi.nlm.nih.gov/35302297/
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Observational / other LOW evidence YELLOWThe Safety and Efficacy of Growth Hormone Secretagogues. ↗Sigalos JT et al.. The Safety and Efficacy of Growth Hormone Secretagogues.. Sex Med Rev. 2018. PMID:28400207.PMID 28400207 ↗Journal Sex Med RevYear 2018Study type Observational / otherEvidence strength LOW evidencePubMed link https://pubmed.ncbi.nlm.nih.gov/28400207/
Score Transparency
0 of 10 approved references (score saturates at 10). More peer-reviewed studies = stronger evidence base.
Method: Q = number of approved references ÷ 10 (capped at 1.0)
Limited — mostly case reports or animal studies
Method: L = mean study-level weight across approved references. Level 1 (meta-analysis / systematic review) = 1.0; Level 2 (RCT) = 0.8; Level 3 (cohort/case-control) = 0.6; Level 4 (case report) = 0.4; Level 5 (animal / in-vitro) = 0.2.
Mixed or neutral — roughly equal benefit and risk signals
Method: D = (sum of risk-scored references − sum of benefit-scored references) ÷ total evidence score, then scaled from [−1, 1] to [0, 1]. 0.0 = pure benefit; 0.5 = neutral; 1.0 = pure risk.
One or more monitoring-level safety signals active
Method: S = 0.5 (neutral baseline) + sum of active signal severity deltas ÷ 10. Severity deltas: Critical = +2.0, High = +1.5, Moderate = +1.0, Low = +0.5. Capped at 1.0.
Final GIRI Score for Ibutamoren (MK-677). Risk level thresholds: Low 0–3.0 · Moderate 3.0–5.5 · High 5.5–7.5 · Critical 7.5–10.
Full methodology & data sources
The GIRI Score is computed entirely from structured data — no editorial scoring or subjective weighting is applied at any step.
- References: Only approved references are counted. Each reference is assigned an evidence level (L1–L5) and a direction (risk / neutral / benefit) by the reference manager or AI classifier.
- Safety Signals: Sourced from regulatory agencies (FDA, EMA, Health Canada, TGA, and others) and pharmacovigilance databases. Only active signals count toward the score.
- Formula version: GIRI Score v3.7.0 — Q × L × D × S × 10.
- Limitations: The score reflects published evidence and recorded signals as of the last update date. It is not a clinical risk assessment and should not replace advice from a qualified healthcare professional.
Risk Level Classification
Based on available regulatory signals and scientific evidence, this ingredient presents a critical safety concern. Regulatory restrictions or bans are in place in multiple jurisdictions.
0–3.0
3.0–5.5
5.5–7.5
7.5–10
The score pin shows exactly where this ingredient falls on the fixed risk scale.
What drove the Critical classification for Ibutamoren (MK-677)
A score of 9.0 places this ingredient in the Critical band. Thresholds: Low 0–3.0 · Moderate 3.0–5.5 · High 5.5–7.5 · Critical 7.5–10.
0 approved references.
Limited — mostly case reports or animal studies (Level 4–5).
Neutral or mixed — benefit and risk signals roughly balanced.
No active signals — S component is at neutral baseline (0.5), contributing no extra risk weight.
No major regulatory restrictions or advisories recorded across monitored jurisdictions (FDA, EMA, Health Canada, TGA, and others).
How are the Low / Moderate / High / Critical thresholds defined?
The four risk levels are fixed score bands. A score is assigned to exactly one level based on where it falls:
| Level | Score | Meaning |
|---|---|---|
| LOW | 0.0 – 2.9 | Sparse or predominantly beneficial evidence. No active safety alerts. |
| MODERATE | 3.0 – 5.4 | Mixed signals — some risk alongside benefit. Caution at high doses or in sensitive groups. |
| HIGH | 5.5 – 7.4 | Multiple studies or regulatory alerts documenting adverse effects. Professional oversight recommended. |
| CRITICAL | 7.5 – 10 | Regulatory restrictions in one or more major jurisdictions. Serious documented harm. Avoid without specialist supervision. |
Thresholds are fixed constants (GIRI_Score_Utils::LEVEL_THRESHOLDS). They do not change per ingredient and are never subject to editorial adjustment.