What IGF-1 Is and Why It's Tracked
IGF-1, insulin-like growth factor 1, is produced mainly by the liver in response to growth hormone. When the pituitary releases growth hormone, the liver converts a portion of that signal into IGF-1, which then circulates in the blood and does much of the actual work associated with growth hormone activity, tissue repair, protein synthesis, and cell growth among them.
IGF-1 is used as the standard proxy for growth-hormone-axis activity because growth hormone itself is released in short pulses, mostly during deep sleep and after exercise, that are genuinely hard to catch on a single blood draw. A GH level drawn at 2pm on a random Tuesday might read near zero even in someone with a perfectly healthy GH axis. IGF-1, by contrast, reflects a more stable downstream signal that builds up and averages out over time, which makes it a far more practical thing to measure with a routine lab draw.
Why Peptide Users Track IGF-1
IGF-1 is the primary marker for growth-hormone secretagogues, compounds that work by prompting the pituitary to release more of its own growth hormone rather than introducing growth hormone directly. This category includes CJC-1295, Ipamorelin, Sermorelin, and Tesamorelin. Because these compounds work upstream of IGF-1, a rising IGF-1 result is generally taken as evidence that the GH axis is actually responding.
On a working protocol, IGF-1 is typically expected to trend upward over several weeks, not overnight. It's a cumulative marker, so a single draw two days into a protocol won't show much of anything. Most people don't see a meaningful shift until they're several weeks in, which is part of why pairing this test with a defined retest interval matters more than checking it too early or too often.
Reading Your Result
IGF-1 numbers are easy to misread in isolation. This is one of the markers where the context around the number matters as much as the number itself.
| Context | What It Means |
|---|---|
| Reference range | IGF-1 reference ranges are age-banded and vary meaningfully by lab and assay. Always compare against the specific age-adjusted range printed on your own lab report, not a single flat number pulled from somewhere else. |
| Rising over a protocol | On a working GH-secretagogue protocol, IGF-1 generally trends upward over several weeks as the axis responds. A flat or falling result over that same window is usually worth a closer look. |
| Very high IGF-1 | Higher isn't automatically better once you're outside the reference range. There is separate longevity research on very elevated IGF-1 later in life, so the general goal on a protocol is restoring a healthier baseline rather than maximizing the number. This is general context, not personalized medical advice. |
A single value tells you little. IGF-1 only becomes useful in comparison. Without a baseline draw before starting a protocol, a follow-up result has nothing meaningful to be measured against. This test is part of the core bloodwork panel for any peptide protocol, not a one-off check.
Testing Conditions
Fasting usually isn't required for IGF-1 specifically, unlike glucose or insulin. That said, for consistency it's worth drawing at a similar time of day for both your baseline and follow-up tests, and using the same lab where possible, since assay methods can differ slightly between labs. BioStackIQ's Analyze My Labs tool can read an uploaded report and flag this automatically, so you don't have to track lab and assay consistency by hand.