How to Test IGF-1 on Growth Hormone (The Numbers You Want)

Growth hormone does almost nothing to your muscle directly. It gets released, travels to your liver, and the liver reads that signal and produces something called IGF-1, which is insulin-like growth factor 1, the hormone that actually tells muscle tissue to take up amino acids and build. So when you inject growth hormone or run a peptide that stimulates your own release, you are not really dosing growth hormone. You are dosing a request to the liver.

That matters because the request can fail at several points along the chain.

The growth hormone can be underdosed or mislabeled. Your pituitary might not respond to the secretagogue. Your liver might not convert well because of low protein intake, poor thyroid function, insulin resistance, or alcohol. And growth hormone itself is almost impossible to measure usefully, because it comes out in pulses and clears within minutes, so a blood draw tells you where you were in a pulse and nothing about the downstream effect.

IGF-1 is the opposite. It binds to carrier proteins in the blood and sits there for hours, which smooths out the pulses and gives you a stable number that reflects what the whole chain actually produced.

The best way to see if the growth hormone or the peptides are taking, actually converting the IGF-1 the way that you want them to is to get your serum IGF-1 taken about four hours after you do your growth hormone and that should give you an idea of where you fall. I cannot point you to a study that validates that specific four hour window, so treat the timing as a practical convention rather than a published protocol. The reason I use it is consistency: IGF-1 responds slowly, so the same interval every time means you are comparing the same point on the curve.

Then you need to know what the number should look like, and this is where most people get confused, because the lab will print a reference range next to your result and that range is not a performance target. It is built from a general population of people who are not injecting anything, and it narrows with age, so a 45 year old can sit at the top of his age bracket and still be nowhere near a level that drives tissue growth.

Most of the time, our target, if we're looking for muscle growth, bodybuilding, we want to get big and strong, we're looking at above 400 is where we want to go. From what I have seen that is the zone where people report real changes in recovery and body composition, and I will say plainly that no study has shown a specific IGF-1 threshold for hypertrophy in humans, so the number is clinical pattern, not literature.

If you're a regular Joe Schmo guy who's just looking to be strong and healthy, I would say around 300, anything lower than 250 probably means that your growth hormone-related peptides aren't doing what they say they're doing. The research hasn't established either of those cutoffs, and I use them because they match what I see with clients who are responding versus clients who are not.

A low number is diagnostic information, not a reason to immediately raise the dose. Work backward through the chain instead.

Check whether the product is real, because counterfeit and underfilled vials are common in the peptide market and a dead vial produces a flat IGF-1 every time.

Then check conversion. Protein intake, thyroid levels, and fasting insulin all affect how well the liver answers the growth hormone signal, and fixing a thyroid problem can move IGF-1 more than doubling the dose would.

Then, and only then, adjust the dose and retest at the same four hour mark four to six weeks later.

Most of what I know about this came out of conversations in the free community, so if you want the rest of it and somewhere to ask, the men's group is here: https://www.skool.com/jh-iron-forge-brotherhood/about