Side-by-side · Research reference

GHRP-6vsMK-677

Side-by-side comparison across mechanism, dosage, evidence, side effects, administration, and stack synergies. Citations on every claim where available.

APhase 1Reviewed10/36 cited

BPhase 2Reviewed13/45 cited

GHRP-6

Hexapeptide GHRP · Strong appetite stimulant

100–200 mcgPer doseBowers 1990

Phase 1Evidence levelBowers 1990

~15 minHalf-lifeMalagón 1999

SQ · Multiple sites · 1–3×/day

MK-677

Oral GHS · Ibutamoren

10–25 mgDaily dose (oral)Nass 2008

Phase 2Evidence levelMurphy 1998 Nass 2008

~24 hrHalf-lifeNass 2008

Oral capsule · 1×/day

01Mechanism of Action

Parameter

GHRP-6

MK-677

Primary target

Ghrelin receptor (GHS-R1a)Bowers 1990

Ghrelin receptor (GHS-R1a)Murphy 1998

Pathway

GHS-R1a → Gαq → Ca²⁺ → GH release; central appetite driveBowers 2002

GHS-R1a → Gαq → Ca²⁺ → sustained GH pulses across 24 hrNass 2008

Downstream effect

GH pulse + strong appetite stimulation; modest IGF-1 elevationBowers 2002

Sustained GH + IGF-1 elevation; appetite stimulation; lean mass preservationNass 2008

Feedback intact?

—

Pulsatile pattern preserved despite long half-lifeMurphy 1998

Origin

Synthetic hexapeptide; first-generation GHRP from Bowers groupBowers 1990

Non-peptide spiroindane-piperidine small molecule designed at MerckMurphy 1998

Antibody development

—

02Dosage Protocols

Parameter

GHRP-6

MK-677

Standard dose

100–200 mcg per injectionBowers 1990

10–25 mg / day oralNass 2008

25 mg used in Nass 2008 elderly trial; 10–15 mg common community dose.

Frequency

1–3× per day

Once daily, oral

Lower / starter dose

50 mcg per dose

5 mg / day

Evidence basis

Phase 1 + clinical practiceBowers 1990

Phase 2 trials (Nass 2008, Murphy 1998)Nass 2008 Murphy 1998

Duration

8–12 weeks on / 4 off

8–16 weeks per cycle (off-cycle to reset receptor sensitivity)

Reconstitution

Bacteriostatic water

Oral, no reconstitution

Timing

Pre-meal preferred for appetite support

Pre-sleep preferred for natural GH pulse alignment

Half-life

~15 minMalagón 1999

~24 hrNass 2008

Once-daily dosing covers 24 hours.

04Side Effects & Safety

Parameter

GHRP-6

MK-677

Hunger

Pronounced — defining feature vs ipamorelin

—

Cortisol elevation

Mild

—

Prolactin elevation

Mild

—

Injection site reaction

Mild

—

Cancer risk

Contraindicated in active malignancy

Contraindicated in active malignancy (GH/IGF-1 axis)

Pregnancy / OB

Avoid

Increased appetite

—

Strong appetite increase via ghrelin agonism

Water retention

—

Mild edema, paresthesias

Glucose tolerance

—

↑ HbA1c +0.3–0.5% in 2-yr elderly trialNass 2008

IGF-1 elevation

—

+50–100% sustainedNass 2008

Cardiovascular

—

No clear adverse signal in trials; congestive heart failure caution

Drowsiness

—

Common, especially during initial weeks

Absolute Contraindications

GHRP-6

·Active malignancy
·Pregnancy / breastfeeding

MK-677

·Active malignancy
·Pregnancy / breastfeeding
·Disrupted hypothalamic-pituitary axis
·Congestive heart failure (caution)

Relative Contraindications

GHRP-6

·Severe insulin resistance (appetite-driven caloric load)

MK-677

·Untreated diabetes
·Pre-diabetes
·Severe insulin resistance

05Administration Protocol

Parameter

GHRP-6

MK-677

1. Reconstitution

Add 2 mL bacteriostatic water to 5 mg vial → 2.5 mg/mL.

Capsule or oral solution. No injection.

2. Injection site

SQ — abdomen. Rotate sites.

Oral. Take with or without food.

3. Timing

Pre-meal for appetite support; pre-sleep for GH alignment.

Pre-sleep preferred — aligns with natural GH pulse.

4. Storage

Lyophilised: room temp. Reconstituted: refrigerate ≤30 days.

Capsule: room temp ≤25 °C, dry place.

5. Needle

29–31G, 4–8 mm insulin syringe.

Monitor HbA1c every 8–12 weeks during chronic use.