- IGFBP-3 binds roughly 80 percent of your circulating IGF-1 and holds it inactive. If your IGFBP-3 is low, your actual free IGF-1 exposure runs higher than your total IGF-1 lab result shows.
- A 2023 study in the Journal of Clinical Endocrinology and Metabolism found the IGF-1:IGFBP-3 ratio detected growth hormone deficiency with 87.5 percent sensitivity. That work was done in short-statured children, so treat it as evidence the ratio carries real information, not as a validated adult peptide-monitoring tool.
- All major GH peptides raise both IGF-1 and IGFBP-3, but not always in proportion. MK-677 tends to raise both in lockstep. Burst-style stacks like ipamorelin may see IGF-1 rise faster than IGFBP-3 in the early weeks.
- Insulin resistance, liver stress, and genetics each suppress IGFBP-3 independently of your peptide protocol. Improving insulin sensitivity can raise your ratio without touching your dose.
- One common variant in the switch that controls how much IGFBP-3 you make sets your baseline before any protocol starts. The low-output version means the same dose delivers more free IGF-1 to your tissues.
IGFBP-3 is the protein that binds roughly 80 percent of your circulating IGF-1 and holds it in an inactive form until your tissues signal that they need it. Most peptide users have never had it tested. That means most people on GH protocols are reading only half the picture when they look at their bloodwork.
The share of circulating IGF-1 that IGFBP-3 holds in bound, inactive form. The remaining 20 percent is the free IGF-1 fraction that actually reaches your tissues and drives downstream signaling.
Total IGF-1 is a useful number. But it tells you the size of the tank, not how much of it is flowing. If your IGFBP-3 is low, whether because of insulin resistance, liver stress, or a genetic variant that lowers how much you make, more of that tank is running free at all times. The amount of IGF-1 reaching your tissues can be substantially higher than the lab result implies.
Here is the metric that captures this: the IGF-1:IGFBP-3 molar ratio, which simply means you convert both proteins to the same counting unit before dividing one by the other, so you are comparing molecules to molecules rather than weight to weight. It is not standard in most peptide monitoring protocols. The Endocrine Society's 2011 Clinical Practice Guideline on Adult Growth Hormone Deficiency (Molitch, Clemmons et al., Journal of Clinical Endocrinology and Metabolism) specifies IGF-1 as the sole biochemical marker for GH monitoring in adults. IGFBP-3 is not in the protocol. But that guideline was written for GH-deficient patients on prescription GH therapy, not for healthy adults running burst-style peptide stacks. The research on the ratio has moved further since 2011, and it tells a different story.
In plain English: Think of IGF-1 as water and IGFBP-3 as a sponge. Total IGF-1 is the total water in the system. Free IGF-1 is the water already dripping out of the sponge and running loose. A small sponge holds less water back than a large one, even if the total water is the same. Testing only total IGF-1 tells you how much water there is. Testing the ratio tells you how much is dripping onto your tissues right now.
Why the IGF-1:IGFBP-3 Ratio Outperforms Total IGF-1 Alone
The strongest evidence for the ratio comes from a 2023 study in the Journal of Clinical Endocrinology and Metabolism by Haj-Ahmad et al. (PubMed 36251796). The team tested how well each marker separated 235 short-statured children with growth hormone deficiency from those without. The ratio picked up 87.5 percent of true cases, and combining IGF-1, IGFBP-3 and the ratio pushed specificity to 97.7 percent. Read that in context: this is a paediatric diagnostic study. It shows the ratio carries information that total IGF-1 alone does not, and the authors are careful about the boundary of that claim.
"The serum IGF-1/IGFBP-3 ratio is a useful marker for the diagnosis of GHD in children who do not have other disorders that may affect serum IGF-1 levels."
Haj-Ahmad M et al., Journal of Clinical Endocrinology and Metabolism, 2023 (PMID 36251796)
Nobody has run the equivalent study in healthy adults on GH peptides. What exists on the high end is population data on IGF-1 itself. The EPIC-Heidelberg cohort analysis (Mukama T et al.) measured IGF-1 in 7,461 stored blood samples, with the main analysis drawn from a case-cohort sample of roughly 3,700 people followed over 17.5 years. Higher IGF-1 was associated with breast cancer (HR 1.25) and prostate cancer (HR 1.31). Its headline finding, which peptide write-ups almost always drop, is that all-cause mortality followed a U-shape: risk rose at both the low and the high end of the IGF-1 range, not just the high one. Note the limit on what this can tell you about the ratio: EPIC-Heidelberg never measured IGFBP-3.
For the peptide user running a GH secretagogue protocol, the direction of concern is different from a deficiency case. You are intentionally raising the GH axis, not correcting a shortfall. But the core principle holds: total IGF-1 without IGFBP-3 leaves half the picture dark.
How to Calculate Your IGF-1:IGFBP-3 Molar Ratio
The calculation requires a unit conversion because labs report the two proteins differently. Most US labs report IGF-1 in ng/mL and IGFBP-3 in ng/mL or ug/mL. The molecular weights are different (7.6 kDa for IGF-1 vs 28.7 kDa for IGFBP-3), so you convert both to nanomoles per liter before dividing.
Molar ratio = [IGF-1 (ng/mL) x 0.13] divided by [IGFBP-3 (ng/mL) x 0.035]
If your lab reports IGFBP-3 in ug/mL or mg/L (these are identical units: 1 mg/L = 1 ug/mL = 1,000 ng/mL), multiply the IGFBP-3 number by 1,000 first to get ng/mL, then apply the formula above.
| Scenario | IGF-1 (ng/mL) | IGFBP-3 (ng/mL) | Molar Ratio | Interpretation |
|---|---|---|---|---|
| Normal adult baseline | 175 | 3,400 | 0.19 | IGFBP-3 comfortably buffers IGF-1. Free IGF-1 fraction is proportionate to total. |
| Protocol running well | 280 | 4,200 | 0.25 | Both markers elevated together. Ratio within expected range for intentional GH axis activation. |
| IGFBP-3 suppressed (same IGF-1) | 280 | 2,200 | 0.47 | Same total IGF-1 as row above, but significantly less buffering. Free IGF-1 fraction substantially higher. |
| IGF-1 outrunning IGFBP-3 | 380 | 3,000 | 0.47 | IGF-1 is rising faster than the binding system. Evaluate insulin status and cycle length. |
| GH axis suppressed | 75 | 1,800 | 0.12 | Both low. Consistent with GH deficiency or testing too early in the protocol before steady state. |
The worked example in row 3 is the one most peptide users miss. Two people with IGF-1 of 280 ng/mL look identical on a standard lab panel. But if one has IGFBP-3 of 4,200 ng/mL and the other has 2,200 ng/mL, their free IGF-1 tissue exposure is dramatically different. The first person has plenty of buffering. The second is running a higher functional IGF-1 load: the tissues see more, even though the total number is exactly the same.
How Different GH Peptides Change the Ratio
Not all GH peptides affect the ratio the same way. The key variable is whether the compound holds IGF-1 up continuously or releases GH in short bursts. Continuous elevation tends to raise IGFBP-3 in parallel, because the liver has sustained time to increase both outputs. Burst-style protocols may see IGF-1 rise faster than IGFBP-3 during the early weeks of a cycle.
MK-677 (Ibutamoren)
The 1996 Chapman et al. trial in the Journal of Clinical Endocrinology and Metabolism showed IGF-1 rising from 141 to 265 ug/L over four weeks of continuous oral 25 mg/day dosing, with IGFBP-3 rising significantly alongside it. Round-the-clock activation of the ghrelin (hunger hormone) receptor keeps the GH signal reaching the liver long enough to raise both markers together. The ratio tends to stay stable on MK-677 unless insulin sensitivity degrades as the protocol extends. The glucose effect documented in the Nass et al. two-year trial can lower IGFBP-3 over time by raising insulin, which then tells the liver to make less of it. See the MK-677 long-term results guide for the two-year picture. For the current regulatory standing and sourcing context, visit the MK-677 peptide page.
CJC-1295 (GHRH analog)
The 2006 Teichman et al. JCEM Phase 1/2 trial showed CJC-1295 with DAC elevated IGF-1 by 1.5 to 3-fold for 9 to 11 days per weekly injection, with confirmed IGFBP-3 increases as part of the broader GH axis response. Holding the pituitary under steady GHRH stimulation appears to lift the liver's IGFBP-3 output alongside IGF-1, which is why the CJC-ipamorelin stack, when working properly, tends to raise both markers together rather than widen the gap between them. Test at trough (mid-week between injections for weekly DAC dosing) to capture a stable plateau rather than a post-injection peak.
GHRP-2 and Ipamorelin
The 2004 Bowers et al. JCEM study of 30-day continuous subcutaneous GHRP-2 infusion in older adults showed IGF-1 rising to a stable elevated plateau, with IGFBP-3 increasing measurably by days 14 and 30. Ipamorelin, the cleaner version that raises cortisol less, has not completed published trials measuring the ratio specifically. The expected behaviour mirrors GHRP-2 on a daily burst schedule: IGF-1 rises in the early weeks while IGFBP-3 catches up over weeks 4 to 6. If ipamorelin is producing no IGF-1 response at all, the bottleneck may be the receptor these compounds act on, the same one ghrelin uses. The GHSR non-responder guide covers that scenario in detail.
The practical implication: if you are four weeks into a burst-style stack and your ratio looks elevated, do not immediately conclude the protocol is dangerous. Your IGFBP-3 may still be catching up to the IGF-1 rise. Test again at week 8 and track the direction. If the ratio is still elevated or rising at eight weeks with IGF-1 stable, IGFBP-3 is not keeping pace, and that is the signal to investigate why before extending the cycle.
How often the IGF-1:IGFBP-3 ratio correctly flagged growth hormone deficiency in the 2023 JCEM study of 235 short-statured children. No equivalent number exists for adults on peptides, because no one has run that study.
Three Reasons Your IGFBP-3 Can Be Suppressed Before You Start Any Protocol
This is the part that surprises most people. Your IGFBP-3 is not just a reflection of your GH axis. It is regulated by insulin, liver function, and a genetic variant that sets your baseline production level independently of everything else. All three can suppress it before you inject your first dose of anything.
1. Insulin resistance suppresses IGFBP-3 at the liver
Chronically high insulin tells the liver to release less IGFBP-3. This is a well-documented pathway: insulin increases how much IGF-1 runs free by shrinking the supply of its carrier protein. If you have metabolic syndrome, carry weight around the middle, or are prediabetic, your IGFBP-3 may already be running low at baseline regardless of your peptide status. Starting a GH secretagogue on top of already-low IGFBP-3 amplifies your free IGF-1 exposure beyond what any total IGF-1 test will show. Improving insulin sensitivity, through carbohydrate management, exercise, or GLP-1 support, can raise your IGFBP-3 and improve your ratio without changing your peptide dose at all.
2. Liver stress reduces hepatic IGFBP-3 output
IGFBP-3 is made mostly in the liver. Liver strain from alcohol, fatty liver disease, or rising liver enzymes on a standard blood panel (AST and ALT) can cut IGFBP-3 output independent of the GH axis. A June 2026 review in Frontiers in Endocrinology by Dominikowski et al. surveying the current evidence base for GH-IGF1 axis peptides explicitly identified "chronic IGF-1 elevation" as a "unifying class effect" across GH secretagogue categories, flagging the absence of long-term safety data in off-label users. If your IGFBP-3 is low while your liver enzymes are trending up, that combination warrants a recheck of both markers before extending any long cycle.
3. Some people simply make less of it, from birth
The gene for IGFBP-3 has an on-switch that comes in two common versions, and which pair you inherited sets how much carrier protein you produce. A 2001 study by Deal, Ma et al. in the Journal of Clinical Endocrinology and Metabolism laid out the gradient: A/A carriers make the most, A/C sit in between, and C/C make the least. The marker is rs2854744, sometimes written A-202C, and it is worth printing here because it is one you can look up in your own raw DNA file. This does not change with protocol or diet. If you are C/C, your baseline ratio leans high compared with someone at the same total IGF-1 who is A/A, and the same protocol puts more free IGF-1 into your tissues. For more on how your IGF-1 receptor genetics compound this, see the IGF-1 receptor genetics guide.
What a Skewed Ratio Actually Signals and What to Do About It
There is an important distinction between a ratio that is temporarily elevated because your IGFBP-3 has not fully caught up to a new protocol, and a ratio that stays elevated because your IGFBP-3 runs low by default. The response is different in each case.
If your ratio is elevated at weeks 3 to 4 of a new burst-style protocol (ipamorelin, CJC-1295 without DAC, sermorelin), retest at week 8. If the ratio has normalized by then, IGFBP-3 caught up. If the ratio is still elevated or rising at eight weeks, the IGFBP-3 is not responding proportionately. That is your signal to check fasting insulin and liver enzymes before extending. The IGF-1 blood test timing guide covers the compound-specific draw windows so you are comparing apples to apples between tests.
If your ratio is elevated before you start any protocol, the driver is metabolic or genetic. Run fasting insulin and HbA1c (your average blood sugar over the past three months) before starting any GH secretagogue. If fasting insulin is above 10 uIU/mL, address insulin sensitivity first. That alone can raise IGFBP-3 and reduce your baseline free IGF-1 load, so that when you do start a protocol, the ratio stays in a proportionate range rather than immediately running hot.
If your ratio is normal but IGF-1 is high in absolute terms, IGFBP-3 is keeping up. Both markers are elevated together proportionately. This reflects a functioning GH axis, which is what a working GH secretagogue protocol is supposed to do. The next question is whether the absolute IGF-1 ceiling warrants a dose adjustment, which is a separate analysis. The most common genetic reason someone's IGF-1 runs high on a standard dose is carrying two copies of the shorter growth hormone receptor, which appears to turn each GH pulse into more IGF-1. The GHR Exon 3 deletion guide covers that in detail.
A high absolute IGFBP-3 is not itself the thing to worry about. The concern is when IGFBP-3 fails to rise in step with IGF-1, leaving more free IGF-1 circulating without its main buffer keeping pace.
| What you see on labs | Most likely meaning | Recommended next step |
|---|---|---|
| High ratio, IGF-1 elevated, IGFBP-3 low | Free IGF-1 excess. IGFBP-3 not buffering the IGF-1 elevation. | Check fasting insulin, liver enzymes, and which version of the IGFBP-3 on-switch you carry. Consider reducing dose or shortening cycle. |
| Normal ratio, both markers elevated | Protocol working. GH axis activated proportionately. | Monitor at steady state. Absolute IGF-1 ceiling is the next variable to assess. |
| Low ratio, both markers low | GH axis not fully activated. Too early in protocol or compound not working. | Retest at weeks 4 to 6. Rule out GHSR non-responder status if still flat at week 8. |
| Elevated ratio at pre-protocol baseline | IGFBP-3 low by default. Insulin resistance or the low-output C/C version of the IGFBP-3 on-switch is the likely reason. | Address insulin sensitivity before starting. Retest IGFBP-3 after 8 to 12 weeks of metabolic intervention. |
Verdict: Test IGFBP-3 alongside IGF-1 on every GH peptide cycle, starting at baseline. The ratio between the two tells you something neither marker can show alone: how much IGF-1 is actually reaching your tissues in free, bioactive form. If the ratio is elevated because IGFBP-3 is suppressed by insulin resistance, that is a metabolic problem you can fix before it becomes a protocol problem. If instead you were born making less carrier protein, you want to know that before you stack protocols that drive IGF-1 further up. Upload your raw DNA file to see which version of the IGFBP-3 on-switch you carry, which growth hormone receptor you have, and the full panel of variables that determine how your tissues respond to GH axis peptides. Or order a saliva kit if you are starting from scratch.
Frequently asked questions
What is the normal IGF-1 to IGFBP-3 molar ratio?
In healthy adults, the molar ratio typically falls between 0.15 and 0.30. A ratio above 0.40 suggests IGFBP-3 is no longer fully buffering the circulating IGF-1, meaning a higher fraction of free IGF-1 is reaching tissues. Calculate your own using: [IGF-1 (ng/mL) x 0.13] divided by [IGFBP-3 (ng/mL) x 0.035]. If your lab reports IGFBP-3 in mg/L or ug/mL, multiply by 1,000 first to convert to ng/mL.
Why is my IGF-1 high but my IGFBP-3 is normal or low?
This pattern means your GH axis is generating more IGF-1 than the carrier-protein system is raising in response. This can happen in the early weeks of a burst-style protocol before IGFBP-3 catches up, or it can reflect an IGFBP-3 that runs low by default because of insulin resistance, liver stress, or the low-output C/C version of the IGFBP-3 on-switch. Retest at eight weeks of steady use. If IGFBP-3 is still flat and IGF-1 remains elevated, check fasting insulin and liver enzymes before continuing.
Does IGFBP-3 increase with growth hormone peptides?
Yes, when GH peptides are working through the full GH-liver axis, both IGF-1 and IGFBP-3 should rise. A 1996 JCEM trial on MK-677 showed both markers rising significantly within four weeks. A 2006 JCEM trial on CJC-1295 confirmed IGFBP-3 elevation alongside IGF-1. However, IGFBP-3 tends to lag behind IGF-1 in the early weeks of a burst-style protocol. Always test at steady state (weeks 4 to 6) before concluding IGFBP-3 is not responding.
How do I lower my IGF-1 to IGFBP-3 ratio?
There are two levers: reduce IGF-1 (lower dose, shorter cycle, switch to a weaker compound) or raise IGFBP-3 (improve insulin sensitivity, reduce liver stress, or allow more time for IGFBP-3 to catch up after starting a protocol). Improving insulin sensitivity through exercise, carbohydrate management, or GLP-1 support is often the fastest way to raise IGFBP-3 without changing your peptide dose at all.
What is the difference between total IGF-1 and free IGF-1?
Total IGF-1 is the sum of all IGF-1 in your blood, both the portion bound to carrier proteins like IGFBP-3 and the small free fraction. About 80 percent is bound and biologically inactive; the remaining 20 percent is free and reaches receptors in your tissues. Total IGF-1 is what standard labs measure. Free IGF-1 tests exist but are expensive and not widely standardized. The molar ratio is the practical proxy for estimating how much of your total IGF-1 is running in free form.
Should I test IGFBP-3 on every GH peptide cycle?
At minimum, test IGFBP-3 once at baseline before starting a GH secretagogue, and once again at four to six weeks of steady protocol use. If the ratio is elevated at baseline, investigate insulin sensitivity before proceeding. If the ratio is elevated at the steady-state check and IGFBP-3 has not risen with IGF-1, check metabolic and hepatic markers before extending the cycle. Two draws per cycle gives you the actionable information without unnecessary testing.
Can a skewed IGF-1:IGFBP-3 ratio increase long-term health risk?
Nobody has measured that directly, and it is worth being plain about it. The EPIC-Heidelberg cohort followed roughly 3,700 people over 17.5 years and found higher IGF-1 associated with raised breast and prostate cancer hazard ratios, plus a U-shaped curve for death from any cause, meaning risk rose at both the low and the high end. But that study never measured IGFBP-3, so it says nothing about the ratio itself. What it supports is a case for not parking your IGF-1 at either extreme over long protocol use. Treat the ratio as a fuller read on your own physiology, not as a validated risk score.
This article is for informational and educational purposes only. It is not medical advice and does not diagnose, treat, cure, or prevent any disease. Consult a qualified healthcare professional before starting any peptide protocol. Individual results vary. Some outbound links are affiliate links, at no extra cost to you.