IGF-1 is the most important lab marker for anyone running GH peptides. This guide covers optimal ranges, timing, what low or high IGF-1 means, and how to act on your results.
Quick Summary - IGF-1 is the primary biomarker for GH axis function -- it reflects cumulative GH exposure better than pulsatile GH measurements - Draw fasted, morning, 24-36 hours after your last GH peptide dose for an accurate baseline - Research optimal range for longevity: 200-310 ng/mL (upper quartile of age-appropriate range) - Low IGF-1 (under 150) on a GH peptide protocol signals inadequate response -- investigate before increasing dose - High IGF-1 (above 350) on protocol warrants dose reduction -- supraphysiologic levels carry long-term risk
If you are running tesamorelin, ipamorelin, CJC-1295, sermorelin, or any GH secretagogue and you have not checked your IGF-1, you are flying blind.
IGF-1 (Insulin-like Growth Factor 1) is produced by the liver in direct response to growth hormone stimulation. Unlike GH itself -- which is released in pulses and fluctuates dramatically throughout the day -- IGF-1 is stable, predictable, and directly reflective of your cumulative GH exposure over the preceding days.
This makes IGF-1 the single most useful lab marker for anyone optimizing GH axis function. It tells you whether your protocol is working, whether your dose is appropriate, and whether you are in a physiologically optimal range or pushing past it.
Growth hormone is released by the pituitary gland in pulses -- most significantly during deep sleep, fasting, and exercise. These pulses are brief and irregular. If you drew blood at a random time of day, your GH level would tell you almost nothing useful.
IGF-1 is different. When GH pulses hit the liver, the liver responds by producing IGF-1. This IGF-1 enters circulation and stays there for hours. The result is a stable measurement that reflects the integrated GH activity over the preceding 24-72 hours.
For GH peptide users, this is exactly what you need. Your peptide dose drives GH pulses. Those pulses drive IGF-1. Your IGF-1 level tells you the net result of all that activity.
Timing is everything. These rules are non-negotiable:
Draw fasted -- minimum 8 hours, preferably overnight fast. Food intake raises insulin which affects GH signaling.
Draw in the morning -- IGF-1 has mild diurnal variation, morning draws are the most stable and comparable across tests.
Draw 24-36 hours after your last GH peptide dose. Drawing within hours of a GH peptide injection captures the post-dose peak, which is significantly higher than your true baseline. This is the single most common testing mistake -- it leads users to think their IGF-1 is higher than it actually is at steady state.
If you inject daily: skip one dose, draw the next morning.
If you inject at bedtime: draw the following morning (approximately 12 hours post-dose) is borderline acceptable, but 24+ hours is more accurate.
Standard lab reference range: Typically 83-233 ng/mL for adults (varies by lab and age bracket). This range is designed to capture the middle 95% of the general population -- it is NOT optimized for performance or longevity.
Research reference ranges for GH peptide users:
Under 100 ng/mL: Deficient range. Significant GH axis dysfunction. If on a GH peptide protocol, likely inadequate dose or poor response. If not on a protocol, consider evaluation for GH deficiency.
100-150 ng/mL: Low-normal. Suboptimal for longevity and performance goals. On a GH peptide protocol, response is below expected.
150-200 ng/mL: Moderate. Acceptable but not optimal for most users with longevity goals.
200-310 ng/mL: Optimal research range. Upper quartile of age-appropriate levels. This is the target for most GH peptide protocols.
310-350 ng/mL: Elevated. Acceptable in younger users, warrants monitoring in users over 50.
Above 350 ng/mL: Supraphysiologic. Dose reduction warranted. Chronically elevated IGF-1 above this range is associated with increased cancer risk in epidemiological literature -- the biology is complex but the precautionary principle applies.
IGF-1 under 150 on a GH peptide protocol:
Do not simply increase dose. First investigate: Are you drawing at the right time (24-36 hours post-dose, fasted, morning)? Is your peptide reconstituted correctly? Is your injection technique adequate? Is your cortisol chronically elevated (blunts GH response)?
If technique is confirmed correct, then assess dose. Tesamorelin at 1mg may need to go to 2mg. Ipamorelin + CJC-1295 may need an additional daily dose (bedtime is most important).
IGF-1 200-310 on protocol:
You are in range. Continue current dose and recheck at 12 weeks. This is the target.
IGF-1 above 350 on protocol:
Reduce dose. If on tesamorelin 2mg, drop to 1mg. If on ipamorelin + CJC-1295 three times daily, drop to twice daily. Recheck IGF-1 in 6 weeks.
IGF-1 declines naturally with age. A 25-year-old with IGF-1 of 280 is in the normal range. A 55-year-old with IGF-1 of 280 is likely above their age-appropriate level. Most labs provide age-stratified reference ranges -- use these when interpreting results.
The research target of 200-310 ng/mL applies broadly but should be adjusted toward the lower end of this range for users over 60, and higher end is acceptable for users under 40.
MyProtocolStack tracks IGF-1 with optimal range set at 200-310 ng/mL, displayed alongside age-appropriate context. Enter your draws with the date and protocol details -- StackAI analyzes your IGF-1 trajectory alongside fasting glucose, HbA1c, and other relevant markers to flag whether your GH protocol is producing the expected pattern or whether something needs adjustment.
How often should I check IGF-1?
Baseline before starting any GH peptide, then at 6-8 weeks (first response check), then at 12 weeks (full cycle assessment). Once stable on a protocol, every 3-6 months is sufficient.
My IGF-1 is in the 300s -- should I stop my protocol?
Not necessarily. 300-350 ng/mL is elevated but not immediately concerning, particularly in users under 50. Reduce dose modestly and recheck in 6 weeks. Above 350 consistently warrants more significant dose reduction.
Can IGF-1 be too low even without GH peptides?
Yes. Low baseline IGF-1 (under 100-120 ng/mL) in the absence of GH peptide use may indicate GH deficiency or significant GH axis dysfunction. This warrants evaluation by a physician, including possibly a stimulation test.
Does semaglutide or tirzepatide affect IGF-1?
GLP-1 agonists can modestly reduce IGF-1 in some users. If combining semaglutide with GH peptides, track IGF-1 closely -- the GLP-1 effect may partially offset the GH peptide effect.
What is the difference between IGF-1 and IGF-BP3?
IGF-1 measures total IGF-1. IGF-1 Binding Protein 3 (IGF-BP3) measures the primary carrier protein. Some practitioners order both for a more complete picture of GH axis function. For most users, IGF-1 alone is sufficient.
The information in this article is for educational purposes only. It does not constitute medical advice. Always consult a licensed healthcare provider before starting any peptide protocol.
Written by Ryan -- Founder, MyProtocolStack. Last Updated: April 2026.
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