Side-by-side · Research reference

MK-677vsTB-500

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 2Reviewed8/46 cited

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

TB-500

Thymosin β4 fragment · Healing

2 mgPer doseGoldstein 2012

Phase 2Evidence levelGoldstein 2012

~2 hrHalf-life

SQ or IM · Multiple sites · 2–3×/week

01Mechanism of Action

Parameter

MK-677

TB-500

Primary target

Ghrelin receptor (GHS-R1a)Murphy 1998

G-actin (sequestering) + cell-surface integrinsGoldstein 2012

Pathway

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

Actin remodelling → cell migration; integrin-linked signaling → angiogenesis; anti-inflammatory cytokine modulationGoldstein 2012 Malinda 1999

Downstream effect

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

Accelerated wound healing, endothelial migration, hair follicle regeneration, cardiac repair (preclinical)Goldstein 2012

Feedback intact?

Pulsatile pattern preserved despite long half-lifeMurphy 1998

Endogenous protein at baseline; supplementation amplifies

Origin

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

17-AA active fragment of endogenous 43-AA thymosin β4 (TMSB4X gene)Goldstein 2012

Antibody development

—

02Dosage Protocols

Parameter

MK-677

TB-500

Standard dose

10–25 mg / day oralNass 2008

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

2 mg per injectionGoldstein 2012

Anecdotal community range; clinical Phase 2 trials used 70–840 mcg/kg IV.

Frequency

Once daily, oral

2× per week (loading); then 1× per week (maintenance)

Lower / starter dose

5 mg / day

1 mg per injection

Evidence basis

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

Animal-strong + Phase 2 dermal/ocular trialsGoldstein 2012

Duration

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

4–8 weeks loading; longer maintenance for chronic injury

Reconstitution

Oral, no reconstitution

Bacteriostatic water, 1–2 mL per 5 mg vial

Timing

Pre-sleep preferred for natural GH pulse alignment

Evening or pre-rest preferred (anecdotal)

Half-life

~24 hrNass 2008

Once-daily dosing covers 24 hours.

~2 hours (estimated; tissue uptake longer)

04Side Effects & Safety

Parameter

MK-677

TB-500

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

—

Cancer risk

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

Theoretical via angiogenesis pathway

Cardiovascular

No clear adverse signal in trials; congestive heart failure caution

—

Drowsiness

Common, especially during initial weeks

—

Pregnancy / OB

Avoid

Injection site reaction

—

Mild erythema, transient pain

GI symptoms

—

Rare nausea (anecdotal)

Lethargy / fatigue

—

Reported anecdotally during loading phase

Antibody formation

—

No data (no long-term human trials)

Long-term safety

—

Unknown beyond Phase 2

Absolute Contraindications

MK-677

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

TB-500

·Active malignancy (theoretical angiogenesis concern)
·Pregnancy / breastfeeding

Relative Contraindications

MK-677

·Untreated diabetes
·Pre-diabetes
·Severe insulin resistance

TB-500

·Cancer history
·Concurrent VEGF inhibitor therapy

05Administration Protocol

Parameter

MK-677

TB-500

1. Form

Capsule or oral solution. No injection.

Add 1–2 mL bacteriostatic water to 5 mg vial → 2.5–5 mg/mL. Roll gently.

2. Site

Oral. Take with or without food.

SQ near injury site (preferred), or systemic SQ (abdomen). Rotate sites.

3. Timing

Pre-sleep preferred — aligns with natural GH pulse.

Evening or pre-sleep is most common anecdotal timing.

4. Storage

Capsule: room temp ≤25 °C, dry place.

Lyophilised: room temp, light-protected. Reconstituted: refrigerate, ≤30 days.

5. Caveat

Monitor HbA1c every 8–12 weeks during chronic use.

27–31G, 4–8 mm insulin syringe.

06Stack Synergy

MK-677

— no documented stacks

TB-500

+ BPC-157

Strong

View BPC-157 →

TB-500 and BPC-157 cover complementary halves of tissue repair: BPC-157 upregulates VEGFR2-driven angiogenesis and fibroblast outgrowth; TB-500 sequesters G-actin to enable endothelial / epithelial migration. The anecdotal canonical "healing stack" — pairs especially well for tendon and ligament injuries.

TB-500: 2 mg SQ · 2× per week
BPC-157: 250–500 mcg SQ · daily
Primary benefit: Combined angiogenesis + cell migration for tendon/ligament/muscle repair