Side-by-side · Research reference
MK-677vsRetatrutide
Side-by-side comparison across mechanism, dosage, evidence, side effects, administration, and stack synergies. Citations on every claim where available.
APhase 2Reviewed13/45 cited
BPhase 2Reviewed10/41 cited
MK-677
Oral GHS · Ibutamoren
Oral capsule · 1×/day
Retatrutide
Triple-receptor agonist · Phase 3
SQ · Abdomen · Once weekly
01Mechanism of Action
Parameter
MK-677
Retatrutide
Primary target
Ghrelin receptor (GHS-R1a)Murphy 1998
GLP-1R + GIPR + Glucagon receptor (triple agonism)Jastreboff 2023
Pathway
GHS-R1a → Gαq → Ca²⁺ → sustained GH pulses across 24 hrNass 2008
Triple-receptor activation → ↑insulin (GLP-1+GIP), ↓gastric emptying, ↑lipid handling, ↑energy expenditure (glucagon component)Jastreboff 2023
Downstream effect
Sustained GH + IGF-1 elevation; appetite stimulation; lean mass preservationNass 2008
Maximal weight loss across class. Glucagon component drives lipolysis and energy expenditure beyond GLP-1+GIP aloneJastreboff 2023
Origin
Non-peptide spiroindane-piperidine small molecule designed at MerckMurphy 1998
Synthetic peptide engineered for balanced affinity at three incretin / glucagon receptorsJastreboff 2023
Antibody development
—
—
02Dosage Protocols
Parameter
MK-677
Retatrutide
Standard dose
10–25 mg / day oralNass 2008
25 mg used in Nass 2008 elderly trial; 10–15 mg common community dose.
12 mg / week (max efficacy)Jastreboff 2023
Phase 2 trial dose. Phase 3 dosing TBD.
Frequency
Once daily, oral
Once weekly
Lower / starter dose
5 mg / day
—
Evidence basis
Phase 2 trials (Nass 2008, Murphy 1998)Nass 2008Murphy 1998
Phase 2 trial; Phase 3 ongoingJastreboff 2023
Duration
8–16 weeks per cycle (off-cycle to reset receptor sensitivity)
Indefinite for chronic indication (presumed)
Reconstitution
Oral, no reconstitution
Investigational; not commercially available
Timing
Pre-sleep preferred for natural GH pulse alignment
Any time of day
Titration schedule
—
2 mg → 4 mg → 8 mg → 12 mg over 16 weeks
04Side Effects & Safety
Parameter
MK-677
Retatrutide
Increased appetite
Strong appetite increase via ghrelin agonism
—
Water retention
Mild edema, paresthesias
—
Cancer risk
Contraindicated in active malignancy (GH/IGF-1 axis)
—
Cardiovascular
No clear adverse signal in trials; congestive heart failure caution
—
Drowsiness
Common, especially during initial weeks
—
Pregnancy / OB
Avoid
Avoid (insufficient data)
Glucose handling
—
Glycemic improvement; rare hyperglycemia from glucagon component
Pancreatitis risk
—
Class warning
Thyroid C-cell tumours
—
Class warning (presumed)
Absolute Contraindications
MK-677
- ·Active malignancy
- ·Pregnancy / breastfeeding
- ·Disrupted hypothalamic-pituitary axis
- ·Congestive heart failure (caution)
Retatrutide
- ·MTC personal or family history (presumed class effect)
- ·Pregnancy / breastfeeding
Relative Contraindications
MK-677
- ·Untreated diabetes
- ·Pre-diabetes
- ·Severe insulin resistance
Retatrutide
- ·Severe gastroparesis
- ·History of pancreatitis
- ·Severe cardiovascular disease (HR signal)
05Administration Protocol
Parameter
MK-677
Retatrutide
1. Form
Capsule or oral solution. No injection.
Investigational peptide. Research vials reconstituted with bacteriostatic water per label.
2. Site
Oral. Take with or without food.
SQ — abdomen, thigh, or upper arm. Rotate weekly.
3. Timing
Pre-sleep preferred — aligns with natural GH pulse.
Once weekly, same day.
4. Storage
Capsule: room temp ≤25 °C, dry place.
Refrigerate 2–8 °C. Light-protected.
5. Caveat
Monitor HbA1c every 8–12 weeks during chronic use.
27–31G, 4–8 mm insulin syringe.