Side-by-side · Research reference
MK-677vsTesamorelin
Side-by-side comparison across mechanism, dosage, evidence, side effects, administration, and stack synergies. Citations on every claim where available.
APhase 2Reviewed13/45 cited
BFDA-ApprovedVerified27/68 cited
MK-677
Oral GHS · Ibutamoren
Oral capsule · 1×/day
Tesamorelin
GHRH Analogue · FDA-Approved
SQ · Abdomen · Once Daily
01Mechanism of Action
Parameter
MK-677
Tesamorelin
Primary target
Ghrelin receptor (GHS-R1a)Murphy 1998
Hypothalamic GHRH receptorsEGRIFTA® (tesamorelin for inje 2010
Pathway
GHS-R1a → Gαq → Ca²⁺ → sustained GH pulses across 24 hrNass 2008
GHRH → Pituitary GH release → Liver IGF-1 synthesisFalutz 2007
Downstream effect
Sustained GH + IGF-1 elevation; appetite stimulation; lean mass preservationNass 2008
Increased GH pulsatility, elevated IGF-1, lipolysis of visceral adipose tissueFalutz 2010
Feedback intact?
Pulsatile pattern preserved despite long half-lifeMurphy 1998
Yes — physiological pulsatility preserved
Origin
Non-peptide spiroindane-piperidine small molecule designed at MerckMurphy 1998
Synthetic 44-AA GHRH analogue with trans-3-hexenoic-acid modification for stabilityEGRIFTA® (tesamorelin for inje 2010
02Dosage Protocols
Parameter
MK-677
Tesamorelin
Standard dose
10–25 mg / day oralNass 2008
25 mg used in Nass 2008 elderly trial; 10–15 mg common community dose.
2 mg / dayEGRIFTA® (tesamorelin for inje 2010
FDA-approved protocol.
Frequency
Once daily, oral
Once daily (morning or pre-sleep)
Aligns with natural GH pulse.
Evidence basis
Phase 2 trials (Nass 2008, Murphy 1998)Nass 2008Murphy 1998
RCT / FDA-approvedFalutz 2007Falutz 2010
Duration
8–16 weeks per cycle (off-cycle to reset receptor sensitivity)
12–52 weeks
VAT returns within months of stopping.
Reconstitution
Oral, no reconstitution
Sterile water per labeling
Preserved at 2–8 °C after reconstitution.
Timing
Pre-sleep preferred for natural GH pulse alignment
Empty stomach, pre-sleep preferred
Half-life
~24 hrNass 2008
Once-daily dosing covers 24 hours.
~26 min (plasma)EGRIFTA® (tesamorelin for inje 2010
Modified vs native GHRH (7 min t½).
03Metabolic / Fat Loss Evidence
Parameter
MK-677
Tesamorelin
Primary fat target
—
Visceral adipose tissue (VAT) — abdominal
Effect on lean mass
—
Modest lean mass preservation / slight increase
Effect reversibility
—
VAT returns within months of stopping
Key publication
—
Falutz et al. NEJM 2007 · Falutz JCEM 2010 · FDA approval 2010Falutz 2007Falutz 2010EGRIFTA® (tesamorelin for inje 2010
04Side Effects & Safety
Parameter
MK-677
Tesamorelin
Increased appetite
Strong appetite increase via ghrelin agonism
—
Water retention
Mild edema, paresthesias
—
Cancer risk
Contraindicated in active malignancy (GH/IGF-1 axis)
Contraindicated in active malignancy (GH/IGF-1 axis); theoretical tumour growth riskEGRIFTA® (tesamorelin for inje 2010
Cardiovascular
No clear adverse signal in trials; congestive heart failure caution
—
Drowsiness
Common, especially during initial weeks
—
Injection site reaction
—
Erythema, pruritus, redness (common)
Fluid retention / Edema
—
Peripheral edema, arthralgia, carpal tunnel (GH-axis effect)
Antibody formation
—
~50% at 26 weeks; non-neutralising in most; rare hypersensitivity (<1%)Sévigny 2018
GI symptoms
—
Nausea, diarrhea (mild, transient)
Absolute Contraindications
MK-677
- ·Active malignancy
- ·Pregnancy / breastfeeding
- ·Disrupted hypothalamic-pituitary axis
- ·Congestive heart failure (caution)
Tesamorelin
- ·Active malignancy or history of treated cancer
- ·Pregnancy
- ·Hypersensitivity to tesamorelin or mannitol
- ·Disruption of hypothalamic-pituitary axis (trauma, tumour, radiation)
Relative Contraindications
MK-677
- ·Untreated diabetes
- ·Pre-diabetes
- ·Severe insulin resistance
Tesamorelin
- ·Untreated diabetes (monitor HbA1c)
- ·Severe carpal tunnel syndrome
- ·Acute critical illness
05Administration Protocol
Parameter
MK-677
Tesamorelin
1. Form
Capsule or oral solution. No injection.
Add 2.1 mL sterile water to 2 mg lyophilised vial. Roll gently — do not shake. Solution should be clear.
2. Site
Oral. Take with or without food.
Subcutaneous — abdomen preferred. Rotate sites (avoid same spot within 2 cm). Avoid navel and waistband area.
3. Timing
Pre-sleep preferred — aligns with natural GH pulse.
Once daily. Preferred: evening, 2–3 hrs post-meal, before sleep — aligns with natural GH secretion pulse.
4. Storage
Capsule: room temp ≤25 °C, dry place.
Lyophilised: room temp, light-protected. Reconstituted: refrigerate 2–8 °C, use within 21 days.
5. Caveat
Monitor HbA1c every 8–12 weeks during chronic use.
27–31G, 4–8 mm insulin syringe. Pinch skin, 45° angle for lean individuals.
06Stack Synergy
MK-677
— no documented stacks
Tesamorelin
+ Ipamorelin
StrongTesamorelin (GHRH analogue) and ipamorelin (GHRP / ghrelin mimetic) act on two distinct receptor systems to amplify GH release synergistically — GHRH receptor + ghrelin receptor. This dual-axis stimulation produces a more robust, sustained GH pulse than either alone while maintaining physiological pulsatility. Ipamorelin is highly selective with minimal cortisol or prolactin elevation, making it the preferred GHRP pairing.
- Tesamorelin
- 2 mg SQ · evening
- Ipamorelin
- 200–300 mcg SQ · same injection
- Frequency
- Once daily, pre-sleep
- Primary benefit
- Maximal GH pulsatility, fat loss, recovery, sleep quality