MK-677 vs IGF-1 LR3
Ghrelin Mimetic (Oral GH Secretagogue) · Long-Acting IGF-1 Analog (Direct IGF-1R Agonist)
Here is how these two compounds compare, based on published research, not marketing claims.
MK-677
An oral GH secretagogue that tells the pituitary to release growth hormone naturally; the upstream approach.
IGF-1 LR3
A modified IGF-1 that delivers the downstream growth factor directly, bypassing the pituitary and liver entirely.
MK-677
134 studies
24 human trials
Not FDA-Approved
IGF-1 LR3
43 studies
1 human trials
Not FDA-Approved
What it does
MK-677
Delivers growth hormone signaling through a pill rather than an injection: the only secretagogue in this class with practical oral bioavailability. Hits the same ghrelin receptor as the injectable compounds, but in a form the gut can absorb. Clinical trials (most notably Murphy et al. and Nass et al.) documented sustained nightly growth hormone and IGF-1 elevation across the 24-hour cycle, alongside the appetite increase and changes in blood sugar handling that ultimately contributed to the failed Alzheimer's trials and the compound's research-only status today.
IGF-1 LR3
Delivers a long-acting form of IGF-1, the growth signal the liver produces in response to growth hormone. Stays active in the body longer than natural IGF-1 because a structural modification reduces how quickly binding proteins clear it.
How it works
MK-677
MK-677 binds the ghrelin receptor (GHS-R1a) on the pituitary gland and stimulates growth hormone release. The mechanism is functionally identical to injectable GH secretagogues like ipamorelin and GHRP-6, but the molecule is engineered for oral bioavailability. The body responds to the GH-releasing signal whether the trigger arrives by injection or by mouth. The downstream effect is increased GH followed by increased IGF-1 production from the liver.
IGF-1 LR3
IGF-1 LR3 is a modified version of insulin-like growth factor 1 with an arginine-to-glutamic acid substitution at position 3 and a 13-amino-acid N-terminal extension. These modifications reduce binding affinity for IGF binding proteins (IGFBPs), extending the biological half-life from minutes to hours. The molecule activates the IGF-1 receptor on muscle, bone, and other tissues, promoting protein synthesis, cell proliferation, and glucose uptake.
How often
MK-677
Oral administration in research protocols. Published studies use daily oral dosing over periods ranging from 8 weeks to 24 weeks. MK-677 is not FDA-approved for any therapeutic indication; no approved product contains ibutamoren mesylate.
IGF-1 LR3
In published research protocols, IGF-1 LR3 has been administered as subcutaneous or intramuscular injection. No FDA-approved product exists; no standardized clinical dosing protocol has been established through regulatory channels.
How strong
MK-677
The oral GH secretagogue. Multiple short-term controlled studies (8 weeks to 6 months) demonstrate GH and IGF-1 elevation, body composition effects, bone turnover markers, and sleep quality improvements (Copinschi 1997 showed 50% increase in stage 4 sleep duration). Reversed diet-induced catabolism in healthy volunteers (Murphy 1998). Fat-free mass gains in obese men (Svensson 1998).
IGF-1 LR3
Potent anabolic signaling through the IGF-1 receptor pathway. The extended half-life means more sustained tissue exposure per administration compared to unmodified IGF-1. Used extensively in cell culture research and animal models for studying IGF-1-mediated growth pathways.
Main tradeoff
MK-677
Oral convenience versus metabolic side effects is the core trade-off. MK-677 raises appetite (ghrelin is the hunger hormone), may elevate blood glucose and reduce insulin sensitivity, and causes water retention. The 24-week Murphy 2008 elderly hip-fracture study was discontinued due to a congestive heart failure signal in that population, the most concerning safety finding in the published literature. Whether the elderly CHF signal applies to healthy younger populations is not established. The compound has not passed Phase III trials despite decades of investigation. Compared to ipamorelin (the selective injectable alternative), MK-677 lacks the clean hormonal selectivity profile.
IGF-1 LR3
Bypasses the body's natural growth hormone axis entirely. Unlike GH secretagogues that stimulate endogenous production, IGF-1 LR3 supplies the downstream growth factor directly. Hypoglycemia risk is the primary safety concern in animal studies due to direct insulin-like activity. No completed human clinical trials for therapeutic use. Not FDA-approved.
Best for
MK-677
- Research interest in oral GH secretagogue mechanisms compared to injectable alternatives
- Research comparing sustained GH elevation (MK-677) versus pulsatile release (ipamorelin, sermorelin)
- Research contexts where the oral-versus-injectable administration question is central
IGF-1 LR3
- Research on IGF-1 receptor signaling and downstream anabolic pathways
- Comparing direct growth factor delivery versus upstream GH stimulation
- Cell culture and animal model studies requiring sustained IGF-1 exposure
How to choose
A good fit for MK-677
- Research on endogenous GH/IGF-1 elevation that preserves the body's natural axis
- Research contexts where oral administration and human trial data are priorities
- Research comparing upstream GH stimulation versus direct downstream growth factor delivery
A good fit for IGF-1 LR3
- Research on direct IGF-1 receptor signaling and downstream anabolic pathways
- Cell culture and animal model studies requiring sustained IGF-1 receptor activation
- Research comparing growth factor delivery strategies (endogenous production vs exogenous supply)
Consider both across time
MK-677 and IGF-1 LR3 represent fundamentally different intervention points in the GH/IGF-1 axis. MK-677 works upstream, telling the pituitary to release GH, which then signals the liver to produce IGF-1 through the body's natural cascade. IGF-1 LR3 skips that entire pathway and delivers the effector hormone directly. MK-677 has more human evidence but weaker anabolic signaling per dose; IGF-1 LR3 has more potent receptor activation but primarily preclinical data and a more consequential safety profile (hypoglycemia, cell proliferation).
Dosing should be determined by a qualified physician who can evaluate individual circumstances. PSI does not provide personalized dosing guidance.
Official dosing references
- DailyMed(NIH drug labels)
- ClinicalTrials.gov
- PubMed
For readers who want the biology: here is the pathway each compound uses to signal the body. This section is optional. The comparison above covers the practical differences.
▶See the biology
- Ghrelin Receptor (GHS-R1a)
- Ghrelin Receptor (GHS-R1a) activates Pituitary Somatotrophs
- Pituitary Somatotrophs connects to Growth Hormone Release
- Growth Hormone Release stimulates Liver IGF-1 Production
- Liver IGF-1 Production connects to IGF-1 Elevation
- Extended Half-Life sustains activation of IGF-1 Receptor
- Reduced IGFBP Binding
- Reduced IGFBP Binding enables Extended Half-Life
- IGF-1 Receptor activates Protein Synthesis
- IGF-1 Receptor activates Cell Proliferation
- IGF-1 Receptor increases Glucose Uptake
- Protein Synthesis connects to Anabolic Signaling; Cell Proliferation connects to Anabolic Signaling
MK-677 binds the ghrelin receptor (GHS-R1a) on the pituitary gland to trigger growth hormone release; in pill form rather than injection.
IGF-1 LR3 activates the IGF-1 receptor directly with reduced IGFBP binding, extending the biological half-life from minutes to hours.
Research Evidence
MK-677 has substantially more human data: multiple controlled trials documenting GH, IGF-1, body composition, bone turnover, and sleep endpoints over 8 to 24 weeks. IGF-1 LR3 is primarily characterized in cell culture and animal models for studying IGF-1 receptor signaling. No completed human therapeutic trials for IGF-1 LR3 have been published. The evidence gap is wide: MK-677 has short-term human efficacy data; IGF-1 LR3 has mechanistic and preclinical data only.
- 1.
If oral administration is required or preferred, MK-677 is the only option. IGF-1 LR3 requires injection.
- 2.
If the research interest is direct IGF-1 receptor activation independent of GH axis function, IGF-1 LR3 provides the more targeted mechanism.
- 3.
If the research interest is GH axis modulation with downstream IGF-1 effects, MK-677 or CJC-1295 are more appropriate than IGF-1 LR3.
- 4.
If selectivity is a priority (avoiding cortisol and prolactin elevation) IGF-1 LR3 does not elevate these hormones, unlike MK-677.
- 5.
For researchers concerned about hypoglycemia risk, MK-677 carries lower acute hypoglycemia risk than direct IGF-1 analogs.
- 6.
Neither compound has established human body composition outcomes data sufficient to draw clinical conclusions.
Key Limitations
- •Neither compound is FDA-approved for anabolic use.
- •MK-677 body composition outcomes data is limited despite being the more studied compound.
- •IGF-1 LR3 human data is extremely limited, most evidence is preclinical.
- •Both compounds carry long-term safety concerns related to sustained IGF-1 signaling and theoretical cancer risk.
- •IGF-1 LR3 hypoglycemia risk requires careful research protocol design.
- •MK-677 cortisol and prolactin elevation limit its selectivity compared to peptide GHRPs.
- •Animal to human translation for anabolic peptide effects has historically been unreliable.
Community Discussion
PSI monitors discussions across peptide research and biohacking communities. These are reported experiences, not clinical evidence.
MK-677
"MK-677 increased my growth hormone levels significantly"
Supported by published data
"It made me hungry all the time and I gained fat"
Supported by published data
"I use it for better sleep and recovery"
Plausible but unproven
Safety Comparison
MK-677's safety profile includes appetite increase, potential glucose and insulin sensitivity effects, water retention, and the elderly hip-fracture CHF signal. IGF-1 LR3's primary safety concern in animal studies is hypoglycemia from direct insulin-like activity, plus the broader concern of sustained IGF-1 receptor activation driving cell proliferation signals. Neither compound has long-term human safety data. The safety profiles are qualitatively different: MK-677 has metabolic concerns; IGF-1 LR3 has metabolic and proliferative concerns.
MK-677
Phase II human data reports water retention, increased appetite, transient insulin resistance, and elevated cortisol and prolactin as the most common effects. Oral administration avoids injection-related risks. Long-term safety of sustained GH and IGF-1 elevation is not established. Cortisol elevation distinguishes it from selective GHRPs like ipamorelin.
IGF-1 LR3
Hypoglycemia risk due to insulin-like activity at IGF-1 receptors, the primary safety concern. Extended half-life amplifies hypoglycemia risk compared to native IGF-1. Human safety data is extremely limited. Theoretical cancer risk from sustained IGF-1R activation. Injectable administration required.
What the Research Suggests
MK-677 and IGF-1 LR3 are complementary research tools that target the same downstream anabolic outcome through opposite points of intervention. MK-677 is the better-characterized compound in humans with more clinical data, oral administration, and a more predictable safety profile, at the cost of selectivity. IGF-1 LR3 provides a more direct mechanistic tool for studying IGF-1 receptor-mediated anabolism, but with a predominantly preclinical evidence base and meaningful hypoglycemia risk. Researchers should select based on which point of the axis they are investigating, not on the assumption that one compound is simply stronger than the other.