IGF-1 testing on a GH peptide cycle
How to test IGF-1 on a GH peptide cycle — why IGF-1 is the right marker, baseline and follow-up timing, target ranges, and what zero movement means.
Updated May 7, 2026 · 5 min read
IGF-1 is the bloodwork marker that tells you whether your GH peptide protocol is doing anything. Without it you're flying blind — relying on subjective feel, sleep quality, and mirror checks to decide if your dose, vendor, and timing are working. With it, you have a number that moves or doesn't.
Why IGF-1, not GH
GH itself is pulsatile — it spikes briefly and disappears. A random GH blood draw at 2 PM tells you almost nothing because GH might be near zero between pulses. To capture GH directly you'd need serial draws across 24 hours, which isn't practical.
IGF-1 (insulin-like growth factor 1) is the downstream signal. The liver produces IGF-1 in response to GH exposure, and IGF-1 has a much longer half-life (around 12–15 hours) — its blood level integrates GH activity over the previous day or two. This makes IGF-1 a clean, single-draw marker for GH-axis activation.
| Marker | Useful for | Drawback |
|---|---|---|
| GH (random) | Almost nothing | Pulsatile, near-zero between pulses |
| GH (serial) | Research only | Multiple draws across 24 hours |
| IGF-1 | Cycle monitoring | Standard practical marker |
| IGFBP-3 | Confirming IGF-1 trends | Optional, less common |
IGF-1 is what you order. Specifically, "IGF-1, LC/MS" or the standard IGF-1 assay your lab offers.
Reference ranges
Adult IGF-1 reference ranges are age-dependent. Rough guidance:
| Age | Typical reference range (ng/mL) |
|---|---|
| 20–30 | 100–280 |
| 30–40 | 90–250 |
| 40–50 | 80–230 |
| 50–60 | 70–210 |
| 60+ | 60–200 |
These vary by lab — always interpret your value against your specific lab's reference range, not a generic chart.
What "good" looks like on cycle
For most off-label users on a GH peptide protocol, the goal is a moderate IGF-1 elevation — typically 25–50% above your baseline, landing in the upper part of the age-adjusted reference range without exceeding it dramatically.
| Pattern | Interpretation |
|---|---|
| No movement from baseline | Protocol isn't working — vendor, dose, or timing issue |
| +10–25% from baseline | Mild response — typical for low-dose Sermorelin |
| +25–50% from baseline | Solid response — typical for Ipa+CJC or Tesamorelin |
| +50%+ from baseline, top of reference | Strong response — watch for side effects |
| Above the reference range ceiling | Supraphysiologic — reduce dose |
The goal is not maximum IGF-1. The goal is meaningful elevation within physiologic range. Pushing IGF-1 above the reference ceiling moves you into territory where the theoretical cancer concerns become less theoretical — chronic supraphysiologic IGF-1 is associated with growth-signaling pathology in long-term observational data.
When to draw blood
A reasonable testing schedule for a 12-week cycle:
| Timepoint | What to test | Why |
|---|---|---|
| Baseline (week 0) | IGF-1, fasting glucose, HbA1c | Establish your starting point |
| Mid-cycle (week 6) | IGF-1, fasting glucose | Confirm the protocol is working, watch glucose drift |
| End-cycle (week 12) | IGF-1, fasting glucose, HbA1c | Document the full response |
| Post-cycle (week 16–20) | IGF-1 | Confirm IGF-1 has returned toward baseline |
Baseline is the most-skipped and most-important draw. Without a baseline you can't interpret a mid-cycle number — "180 ng/mL" means very different things if your baseline was 110 vs 175.
Draw timing
For IGF-1 specifically, the timing is forgiving — you don't need to fast for IGF-1 alone, and the time-of-day doesn't matter much because of the long half-life. If you're also drawing fasting glucose and insulin in the same panel, you'll need to fast (8–12 hours) for those.
Most users batch the panel — IGF-1 + fasting glucose + HbA1c + a basic metabolic panel — into a single morning fasted draw.
What no movement means
If your week-6 or week-12 IGF-1 hasn't moved from baseline, troubleshoot in this order:
- Vendor quality. Underdosed or fake peptides are the most common cause of zero IGF-1 response. See vendor quality checks.
- Reconstitution and storage. Check your math, check your refrigeration, check that you're drawing the dose you think you're drawing. Use the reconstitution calculator.
- Timing. Eating before injection blunts GH release sharply. Confirm you're injecting on an empty stomach. See best injection timing.
- Dose. Some users need the upper end of the dose range to produce a measurable IGF-1 response.
- Individual response. A small fraction of users have blunted GH-axis responsiveness — typically older users or those with pituitary issues. If everything else checks out and IGF-1 still doesn't move, secretagogues may simply not be the right tool for you.
Other markers worth tracking
| Marker | Why |
|---|---|
| Fasting glucose | GH peptides can shift glucose; track at baseline and mid-cycle |
| HbA1c | Longer-window glucose marker; baseline and end-cycle |
| Fasting insulin | Optional; useful for detecting insulin resistance drift |
| IGFBP-3 | Optional; confirms IGF-1 trend if results are ambiguous |
| Prolactin | Useful if running GHRP-2 or GHRP-6 long-term |
| Cortisol (AM) | Same as above |
For most users on Sermorelin or Ipa+CJC, IGF-1 + fasting glucose + HbA1c is sufficient. For users on Tesamorelin, MK-677, or GHRP-2/6 long-term, the broader panel makes more sense.
A practical takeaway
Don't run a GH peptide protocol blind. The bloodwork is the difference between knowing your protocol works and hoping it does. A baseline + mid-cycle + end-cycle IGF-1 panel costs less than a single vial of peptide and tells you more than three months of feel checks.