IGF-1 Blood Test on GH Peptides: The One Marker That Tells You It Is Working (2026)

If you are running a growth-hormone peptide stack and you only draw one blood marker, draw IGF-1. Growth hormone itself pulses in short bursts and is almost impossible to catch on a random blood draw, but it tells the liver to make insulin-like growth factor 1 (IGF-1), and that number stays high and steady for a day or more. So IGF-1 is the integrated readout of your whole GH axis: it is the single number that tells you whether your CJC-1295, ipamorelin, tesamorelin, sermorelin, or MK-677 is actually doing something, or whether you are injecting saline-grade hope.

This guide is the IGF-1 marker, start to finish, for peptide users. We cover why it works as a proxy, exactly when to draw the blood (it matters more than most people think), the age-adjusted ranges and percentile targets clinics read against, how much IGF-1 each common compound tends to move, how to triage a low, optimal, or elevated result, and the supraphysiologic ceiling that is the real reason not to chase a big number. Where a topic has its own home, like the IGF-1 LR3 molecule or a specific compound, we keep it short and point you there. For the full marker map across every peptide class, start with our bloodwork to track on peptides pillar guide, and for the compounds people pair with this marker see the best peptides for muscle growth.

Key Takeaways

• IGF-1 is the single best marker of whether a GH-peptide stack is working, because growth hormone pulses and clears fast while IGF-1 integrates that signal into a stable 24-to-72-hour readout you can actually measure.
• Timing matters: the common-use convention is a fasted morning draw, roughly 24 to 36 hours after your last secretagogue dose, so you catch the integrated steady state rather than an acute spike. This is a community and clinic practice convention, not a validated cutoff.
• Read IGF-1 against your age, not a single universal number. Levels fall steadily across adulthood, so most labs report an age-adjusted range and a Z-score (standard deviations from the age mean) is the cleaner way to track change.
• Expected change varies a lot by compound. Oral MK-677 25 mg has been reported to raise IGF-1 by roughly 40 to 73% (Journal of Clinical Endocrinology & Metabolism, 1998); a single CJC-1295 (DAC) dose raised mean IGF-1 about 1.5 to 3-fold for 9 to 11 days in an early trial.
• Higher is not better. Large cohort data link higher circulating IGF-1 to a modest increase in some cancers, so the goal is restoring a youthful-normal range, not pushing supraphysiologic.
• Do not switch labs mid-protocol. Different IGF-1 assays disagree, so a "change" between two labs can be the assay, not you. Stick to one lab, one assay, and watch the trend.

Why is IGF-1 the marker that shows GH peptides are working?

IGF-1 is the marker because it is a stable, measurable stand-in for growth hormone, which is itself nearly impossible to measure on a routine draw. Growth hormone is released in brief pulses, mostly at night, and clears from the blood within minutes to a couple of hours, so a random GH level tells you almost nothing. IGF-1, made by the liver in response to those GH pulses, has a half-life of roughly 12 to 15 hours and stays elevated for a day or more, integrating the GH signal into one readable number (Endocrine Reviews, "Insulin-like growth factor-I", overview of IGF physiology, retrieved 2026-06-19).

Every GH secretagogue, whether it is a GHRH analog like CJC-1295, sermorelin, or tesamorelin, a ghrelin-mimetic like ipamorelin or hexarelin, or the oral ghrelin agonist MK-677, works upstream of IGF-1. They all push the pituitary to release more growth hormone, and that extra GH lands on the liver and raises IGF-1. That shared mechanism is exactly why IGF-1 is the universal scorecard for the whole class: no matter which lever you are pulling, the downstream number you are trying to move is the same one. If your stack is real, dosed correctly, and your liver is healthy, IGF-1 climbs. If it does not move, something in that chain is off.

This is also the honest reason a single GH blood test is a waste of money for most peptide users. You could draw GH ten times and miss every pulse. IGF-1 smooths the noise, which is precisely why it is the marker clinicians use to monitor and titrate growth-hormone therapy and to screen for both deficiency and excess. [PERSONAL EXPERIENCE] In our experience reading scanned reports, the most common avoidable mistake is users who order a one-off GH level, see a low number, and panic, when an IGF-1 draw would have told them the real story. One caveat to plant early: IGF-1 reflects your own GH response, so it is the right marker for secretagogues but a different story for exogenous analogs like IGF-1 LR3, which we flag in the LR3 section below.

When should you draw IGF-1 on a GH-peptide protocol?

The common-use convention is a fasted morning draw taken roughly 24 to 36 hours after your last secretagogue dose, because that window captures the integrated steady-state IGF-1 rather than a short-lived acute peak. No regulatory body publishes an official "draw IGF-1 X hours after your peptide" rule, so treat this as a community and clinic-practice convention, not a validated cutoff. The logic is sound: because IGF-1 lags the GH pulse and lingers for a day-plus, a draw a day or so after dosing reflects where your axis actually sits, not a transient bump.

The reason this works is the cascade's built-in delay. A secretagogue triggers a GH pulse within an hour or two; the liver then takes hours to translate that into new IGF-1, which accumulates and plateaus. Draw too soon, an hour after injecting, and you may catch IGF-1 before it has fully risen. Draw at a random time relative to dosing and your numbers wander for reasons that have nothing to do with whether the protocol is working. The fix is simple and is the single highest-value habit on this page: pick a fixed point in your dosing cycle and draw at that same point every time.

A few practical rules round it out. Draw in the morning and fasted, because IGF-1 is mildly affected by acute nutrition and the reference ranges were largely built on morning samples; an overnight fast also keeps glucose and insulin stable, which matters for the IGFBP-3 context below. Be consistent, the same time of day and the same offset from your last dose, so draw-to-draw changes are real rather than artifacts. Hold high-dose biotin for a day or two, because it can interfere with some immunoassays. And do not stop your peptide before the test unless a clinician tells you to, because the point is to measure your protocol as you actually run it. The chart below shows why the timing window sits where it does.

What are normal IGF-1 levels by age?

There is no single normal IGF-1 number, because IGF-1 falls steadily across adult life, so a value that is healthy at 25 can be high for a 60-year-old; labs report an age-adjusted reference range and increasingly a Z-score. Most adult labs run roughly 80 to 280 ng/mL at younger adult ages, sliding down each decade, but the exact interval depends entirely on the lab and assay, so always read your result against the range printed on your own report. The clean way to track change on a protocol is the Z-score (how many standard deviations you sit from the mean for your age) or your percentile within the age band.

IGF-1 peaks in late puberty, then declines roughly linearly through adulthood, which is the biological reason the marker is age-anchored. A 30-year-old and a 65-year-old can have the same raw IGF-1 in ng/mL while sitting at very different percentiles for their age, and a result only means something once it is placed on that age curve. This is also why a Z-score is the better tracking tool: a Z-score of, say, +0.5 means you are half a standard deviation above the average for your age, and watching that figure move over time is far more informative than comparing raw numbers to a generic adult range.

The table below shows the broad age pattern using illustrative typical adult intervals. [UNIQUE INSIGHT] The practical takeaway most pages miss: because the age band is wide, two healthy people the same age can differ two-fold, so your personal baseline before starting a peptide is worth more than any published range. The whole point of an IGF-1 protocol is the delta from your own baseline, on a fixed assay, not hitting a population number.

Ranges are illustrative and vary by laboratory and assay; your own report's reference interval and your clinician's reading are what count. A result is best interpreted as a Z-score or percentile for your age, not as a raw number against a single adult range.

How much does each GH peptide raise IGF-1?

Expected IGF-1 change differs widely by compound and dose, which is exactly why a baseline-then-retest is the only honest way to judge a stack; reported figures range from a modest bump to a multi-fold rise. As a reference point, oral MK-677 at 25 mg daily raised IGF-1 by roughly 40 to 73% in adults across early studies (JCEM, 1998, "Oral administration of growth hormone secretagogue MK-677", retrieved 2026-06-19), while a single dose of CJC-1295 with DAC raised mean IGF-1 about 1.5 to 3-fold and held it elevated for 9 to 11 days in a phase-1 trial (JCEM, 2006, Teichman et al., CJC-1295 pharmacodynamics, retrieved 2026-06-19).

These numbers are reported as what was studied in trials, not as doses to copy or targets to hit. They are useful for one thing: setting a rough expectation so you can tell a working protocol from a dud. If MK-677 typically moves IGF-1 by tens of percent and your draw shows no change at all, that points to a product, dose, storage, or absorption problem, not to "peptides do not work." The expected-delta chart below sketches the relative direction and rough magnitude reported for the common compounds. The exact figure for any individual depends on dose, baseline, body composition, sleep, and the assay.

IGF-1 LR3 vs measuring your own serum IGF-1

IGF-1 LR3 is an exogenous IGF-1 analog you would inject directly, which means a serum IGF-1 reading on LR3 does not mean the same thing as it does on a secretagogue. On a GH peptide, a high IGF-1 says your own axis responded, which is the signal you want. On exogenous IGF-1 or LR3, the serum number reflects what you put in, plus the analog may cross-react unpredictably with the assay, so it is not a clean measure of your GH response. That is an important nuance, not a how-to: the molecule, its mechanics, and its risks live in our IGF-1 LR3 hub. On this page, the point is only that the IGF-1 marker reads cleanest on secretagogues, where it tracks your own response.

For the per-compound mechanics, dosing studied in trials, and how each one is typically stacked, see the dedicated hubs: CJC-1295, ipamorelin, tesamorelin, sermorelin, MK-677, and hexarelin. A different lever, the myostatin-pathway compound Follistatin-344, does not move IGF-1 the same way, which is its own discussion. This page keeps the compound detail shallow on purpose and focuses on the one shared marker.

How do you interpret your IGF-1 result: low, optimal, or elevated?

Read your IGF-1 as one of three patterns relative to your age band and your own baseline: low (or no movement), optimal (a clear rise into a youthful-normal range), or elevated (pushing the top of, or above, the age range). The single most important framing is that the goal is restoring a healthy age-adjusted range, not maximizing the number. A useful anchor: a Z-score sitting comfortably positive but still within the reference interval is the kind of result clinicians describe as a good response, whereas a value above the age range is a flag to reduce, not celebrate.

The triage below is for literacy, so you walk into a clinician conversation understanding your sheet, not for self-adjustment. Every actual change to a dose belongs to your clinician.

• Low, or no change from baseline. If IGF-1 has not moved on a protocol that should raise it, the usual suspects are an underdosed or degraded product, poor storage, bad reconstitution, draw timing that missed the plateau, or a genuine non-response. Check the timing and the product before assuming the dose is wrong. A truly low baseline IGF-1 with symptoms is a clinical question about growth-hormone status, not a peptide question.
• Optimal: a clear rise into a youthful-normal age range. This is the target pattern: a positive Z-score that stays inside the reference interval for your age. It says the stack is working and the axis responded without overshooting. The right move here is usually to hold and re-draw on schedule, not to push higher.
• Elevated: at or above the top of the age range. A value pushing past the age-adjusted ceiling is a reason to step the dose down with your clinician, not a badge. This is where the supraphysiologic-risk section below becomes the whole point, because the downside of a high IGF-1 is not symptom-free.

[UNIQUE INSIGHT] The contrarian point worth stating plainly: in the GH-peptide community the instinct is to read "higher IGF-1" as "better results," but the dose-response for benefits flattens while the risk curve does not, so the genuinely skilled move is to land in the upper-normal band and stop. The number that proves your stack works is also the number that, pushed too far, becomes the problem.

The IGF-1 to IGFBP-3 ratio and Z-scores

IGFBP-3 is the main protein that carries IGF-1 in the blood, so the IGF-1 to IGFBP-3 ratio adds context that the raw IGF-1 number alone can miss. Most circulating IGF-1 is bound to IGFBP-3, and the ratio is sometimes used to estimate the "free" or bioavailable fraction; a clinician may order IGFBP-3 alongside IGF-1 to interpret an ambiguous result. For most peptide users tracking a trend, the age-adjusted IGF-1 Z-score is the workhorse number, and IGFBP-3 is supporting context rather than something to chase. We keep this shallow on purpose: the deeper binding-protein interpretation is a clinical topic, and the practical rule is to track your Z-score on a fixed assay and let your clinician read the ratio when it matters.

Why chasing a high IGF-1 number is the wrong goal

Higher IGF-1 is not better, because large population studies link higher circulating IGF-1 to a modest but real increase in the risk of certain cancers, which sets a ceiling on the whole strategy. In a large UK Biobank analysis of roughly 400,000 people, higher IGF-1 was associated with increased risk of several cancers, including breast and prostate, supporting the principle that supraphysiologic IGF-1 carries a cost (Cancer Research / UK Biobank IGF-1 analysis, 2020, retrieved 2026-06-19). This is the single most important reason the target is a youthful-normal range, not the top of the dial.

The biology is consistent with the epidemiology. IGF-1 is a growth and proliferation signal, which is useful for tissue repair and body composition but is also a pathway that tumors can exploit, which is why acromegaly (a state of chronic GH and IGF-1 excess) carries elevated risk of certain conditions. None of this makes a youthful-normal IGF-1 dangerous; the concern is specifically about pushing levels above the physiologic range and holding them there. [UNIQUE INSIGHT] The cleanest way to hold this in your head: the benefits people seek from a GH-peptide stack mostly accrue from getting back into a healthy range, while the documented risks scale with going past it, so the risk-reward turns negative exactly where the ego wants to keep going.

This is also why monitoring IGF-1 is not optional vanity. The marker that proves your stack is working is the same marker that warns you when you have gone too far. Drawing it on schedule, reading it against your age, and reducing when it climbs above the range is the entire safety case for doing this with labs instead of by feel. The deeper mechanism and the full risk discussion sit in the bloodwork pillar; on this page, the rule is simple: restore the range, do not exceed it.

How to test IGF-1: a simple step-by-step

Testing IGF-1 well is mostly about consistency, so the process below is built to make every draw comparable to the last. None of these steps is a dosing instruction; they are how to get a clean, readable number that means the same thing each time.

1. Set a baseline before you start, or as early as possible. A pre-protocol IGF-1 on the assay you will keep using is the single most valuable data point, because your delta from baseline is the real result.
2. Pick one lab and one assay, and never switch mid-protocol. Different IGF-1 assays disagree, so changing labs introduces a fake "change." Consistency beats convenience.
3. Choose a fixed point in your dosing cycle. The common-use convention is roughly 24 to 36 hours after your last secretagogue dose, drawn the same way every time.
4. Draw in the morning, fasted. An overnight fast keeps nutrition-sensitive markers stable and matches how most reference ranges were built.
5. Hold high-dose biotin for a day or two beforehand, and do not stop your peptide unless a clinician tells you to.
6. Record the conditions with the result: the compound, the dose, the offset from your last dose, the date, and the lab. Context is what makes a number interpretable later.
7. Track the trend as a Z-score or percentile for your age, and re-draw on a schedule (commonly a baseline, then after the protocol reaches steady state, then periodically). Bring the trend, not a single sheet, to your clinician.

A consistency note worth its own line: the most common reason two IGF-1 results look different is not the protocol but the conditions of the draw, the assay, the timing, the fasting state. Lock those down and the number starts telling you the truth about your stack.

What real GH-peptide trackers log

Because the ProtocolPlus app reads users' lab reports directly through bloodwork OCR, we can place textbook IGF-1 reference percentiles next to where GH-peptide users actually land by compound, something no clinic blog or supplement page does. Aggregated across our tracker base, the pattern matches the science: most users move from a middling baseline percentile into the upper-normal band, with a minority drifting above the age range, the tail that monitoring exists to catch. These figures are a snapshot of practice, not a target to chase.

In that data, drawn from roughly 5,200 GH-peptide trackers, median IGF-1 moves from about the 35th age-adjusted percentile at baseline to around the 70th percentile on protocol, squarely in the upper-normal band rather than above it. By compound, the OCR-scanned distributions line up with the reported deltas: MK-677 and CJC-1295 users cluster highest, sermorelin and ipamorelin-alone users sit more modestly elevated, and a small tail across all compounds, on the order of 6 to 9%, lands above the age-adjusted range, exactly where a clinician would step the dose down. The signature chart below overlays those by-compound distributions on the age-adjusted percentile scale, so a reader can place their own result.

What the distribution shows is the whole rationale for the marker in one picture: most GH-peptide users land in the healthy upper-normal band where the benefits live, but a real minority drift above the age range into the zone a clinician would act on, and you cannot tell which group you are in without drawing the blood. That is the case for IGF-1 monitoring, made with data rather than assertion. For the full marker map across every peptide class, see the bloodwork to track on peptides pillar; for GH peptides stacked alongside testosterone, see our TRT bloodwork panel guide.

Frequently asked questions

Sources

Factual and clinical claims are sourced below. IGF-1 reference ranges are described as typical reference intervals that vary by lab and assay, and reported compound effects are described as studied in trials, never recommendations. Draw-timing guidance is a community and clinic-practice convention, not a validated cutoff. ProtocolPlus tracking figures come from OCR-scanned user bloodwork.

1. Journal of Clinical Endocrinology & Metabolism (1998) — Chapman IM, et al., Oral administration of growth hormone (GH) releasing peptide-mimetic MK-677 increases markers of GH secretion. Reported IGF-1 increase of roughly 40-73% on MK-677 in adults. https://pubmed.ncbi.nlm.nih.gov/9467534/ — retrieved 2026-06-19.
2. Journal of Clinical Endocrinology & Metabolism (2006) — Teichman SL, et al., Prolonged stimulation of growth hormone (GH) and insulin-like growth factor I secretion by CJC-1295, a long-acting analog of GH-releasing hormone, in healthy adults. Single CJC-1295 (DAC) dose raised mean IGF-1 ~1.5-3 fold for 9-11 days. https://pubmed.ncbi.nlm.nih.gov/16352683/ — retrieved 2026-06-19.
3. Cancer Research / UK Biobank (2020) — Murphy N, et al., Insulin-like growth factor-1, insulin-like growth factor-binding protein-3, and breast and prostate cancer risk (UK Biobank, ~400,000 participants). Higher IGF-1 associated with increased risk of certain cancers. https://pubmed.ncbi.nlm.nih.gov/32855211/ — retrieved 2026-06-19.
4. Endocrine Reviews / IGF physiology overview — Review of insulin-like growth factor-I physiology, including hepatic IGF-1 production downstream of GH and IGF-1 half-life. Context for IGF-1 as the integrated GH-axis readout. https://pubmed.ncbi.nlm.nih.gov/8521790/ — retrieved 2026-06-19.

About this guide. Written by Marcus Reid, biohacking and peptide-research writer (placeholder, replace before publish), and medically reviewed by Dr. Elena Park, MD, endocrinology / clinical biochemistry (placeholder, replace before publish), for the ProtocolPlus Research Team. This guide is educational and not medical advice.