Side-by-side · Research reference
HGH Fragment 176-191vsPT-141
Side-by-side comparison across mechanism, dosage, evidence, side effects, administration, and stack synergies. Citations on every claim where available.
AAnimal-StrongHUMAN-REVIEWED28/59 cited
BFDA-ApprovedHUMAN-REVIEWED13/41 cited
HGH Fragment 176-191
GH Fragment · Pre-Clinical
SQ · IP (animal) · Oral (tested)
PT-141
MC4R Agonist · FDA-Approved (HSDD)
SQ · Abdomen / thigh · ≥45 min before sex
01Mechanism of Action
Parameter
HGH Fragment 176-191
PT-141
Primary target
Beta-3 adrenergic receptors on adipocytesHeffernan 2001
Melanocortin-4 receptor (MC4R) in hypothalamusSimerly 2023VYLEESI (bremelanotide injecti 2019
Pathway
Fragment → β3-AR upregulation → Enhanced lipolytic sensitivityHeffernan 2001
MC4R agonism in paraventricular nucleus → autonomic + neuroendocrine sexual arousal pathwaysSimerly 2023
Downstream effect
Increased lipolysis and beta-3 AR mRNA expression without IGF-1 axis activation
Increased sexual desire and arousal; central rather than peripheral mechanismClayton 2015
Feedback intact?
N/A — does not interact with GH/IGF-1 axis
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Origin
Synthetic peptide derived from hGH residues 176-191; AOD9604 includes N-terminal tyrosine (177-191)Cox 2015
Cyclic 7-AA peptide derived from α-MSH (agonist Ac-Nle-Asp-His-D-Phe-Arg-Trp-Lys-OH cyclic)VYLEESI (bremelanotide injecti 2019
Antibody development
Not reported in available studies
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02Dosage Protocols
Parameter
HGH Fragment 176-191
PT-141
Animal dose (IP)
Not specified (14-day chronic administration)Heffernan 2001
Obese mice, daily IP injection.
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Human equivalent dose
Not established — no published human RCTs
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Frequency
Once daily (animal models)
PRN, max 8 doses / month
Evidence basis
Animal studies only
FDA-approved (HSDD pre-menopausal women)VYLEESI (bremelanotide injecti 2019Clayton 2015
Detection window
50 pg/mL LOD in urine; stable metabolite extends detectionCox 2015
WADA-banned; anti-doping testing available.
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Oral bioavailability
Demonstrated efficacy in animal oral administrationNg 2000
Potential for oral therapeutic development.
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Standard dose
—
1.75 mg SQVYLEESI (bremelanotide injecti 2019
Single dose ≥45 min before anticipated sexual activity. Max 1 dose / 24 hr.
Lower / starter dose
—
1 mg (off-label)
Duration
—
PRN; reassess if no benefit after 8 doses
Reconstitution
—
Pre-filled commercial pen (Vyleesi). Research vial: bacteriostatic water.
Timing
—
≥45 min before sexual activity
03Metabolic / Fat Loss Evidence
Parameter
HGH Fragment 176-191
PT-141
Weight gain reduction
50% reduction vs control (15.8 ± 0.6 g vs 35.6 ± 0.8 g)Ng 2000
Obese Zucker rats, 19 days oral administration.
—
Body fat reduction
Significant decrease in body weight and body fat in obese mice (14 days)Heffernan 2001
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Lipolytic activity
Increased adipose tissue lipolytic activityNg 2000
Direct measurement in treated animals.
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Insulin sensitivity
No adverse effect — euglycemic clamp confirmedNg 2000
Contrasts with intact hGH diabetogenic effects.
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IGF-1 impact
No elevation — fragment does not activate GH/IGF-1 axis
—
Beta-3 AR dependency
Effect abolished in β3-AR knockout miceHeffernan 2001
Confirms β3-AR as primary mechanism.
—
Human evidence
None published — pre-clinical only
—
04Side Effects & Safety
Parameter
HGH Fragment 176-191
PT-141
Human safety data
Not available — no published human trials
—
Metabolic profile
Six metabolites identified; CRSVEGSCG most stableCox 2015
Detection window implications for doping control.
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Flushing
—
Common, transient
Injection site reaction
—
Erythema, mild pain
Headache
—
Common
Hyperpigmentation (focal)
—
Rare focal skin darkening; reversible after discontinuationVYLEESI (bremelanotide injecti 2019
Hypertension (transient)
—
Mean ↑6 mmHg systolic peaking ~4 h post-dose; resolves within 12 hVYLEESI (bremelanotide injecti 2019
Pregnancy / OB
—
Contraindicated
Cardiovascular disease
—
Use caution; transient BP rise
Absolute Contraindications
HGH Fragment 176-191
- ·Competitive athletes (WADA-banned)Cox 2015
PT-141
- ·Uncontrolled hypertension
- ·Known cardiovascular disease (caution)
- ·Pregnancy
Relative Contraindications
HGH Fragment 176-191
- ·Absence of human safety data — experimental use only
PT-141
- ·Pre-existing hyperpigmentation disorders
- ·MC4R-pathway-dependent psychiatric conditions
05Administration Protocol
Parameter
HGH Fragment 176-191
PT-141
1. Route
Subcutaneous injection primary route in research context. Oral administration demonstrated efficacy in animal models at 500 mcg/kg.
Vyleesi: pre-filled auto-injector. Research vial: 2 mL bacteriostatic water per 10 mg → 5 mg/mL.
2. Frequency
Once daily dosing used in animal studies. Timing not specified; GH-independent mechanism suggests flexibility.
SQ — abdomen or thigh.
3. Duration
Animal protocols: 14–19 days. Human duration not established — no published trials.
≥45 min before sexual activity for peak effect. Effect persists ~6–8 h.
4. Storage
Lyophilized peptide storage per standard peptide protocols. Metabolite stability suggests refrigerated reconstituted solution viable.
Vyleesi: room temp ≤30 °C. Research vial: refrigerate after reconstitution.
5. Detection
Detectable in urine via SPE-LC-MS at 50 pg/mL LOD. Extended detection window via stable metabolite CRSVEGSCG.Cox 2015
Auto-injector (Vyleesi) or 29–31G, 4–8 mm insulin syringe.