There Are Only 3 Ways To Increase Your IGF-1 (How To Pick The Right One)

Your pituitary gland is not just a hormone factory. It is a factory with a built-in production limit, and understanding that limit is the key to understanding every growth hormone compound on the market.

Here is the full chain first. Your hypothalamus releases something called GHRH, which stands for growth hormone releasing hormone, and this is the upstream signal that tells your pituitary to make and release growth hormone. That growth hormone travels through the bloodstream to your liver, where it triggers the production of something called IGF-1, which is insulin-like growth factor 1, the downstream molecule that actually drives most of the tissue-level effects people associate with growth hormone: muscle protein synthesis, fat mobilization, recovery. IGF-1 then feeds back up to the brain and tells it to release something called somatostatin, which is the brake signal that tells the pituitary to slow down. That loop, hypothalamus to pituitary to liver to IGF-1 back to brain, is the entire system. Every compound we are about to talk about plugs into one specific point in that chain.

The first category is GHRH analogs, which includes Sermorelin, CJC-1295, and Tesamorelin. These work by mimicking the natural GHRH signal at the pituitary, telling it to produce and release more of your own growth hormone. Because the signal is going into the top of the natural loop, the entire feedback system stays intact. When IGF-1 rises, somatostatin rises, the pituitary slows, and your output stabilizes. This is not a flaw in the drug, it is just your body's regulation working exactly as designed.

This means there is a ceiling, and it is your biology's ceiling, not a dosing ceiling, and no amount of additional peptide pushes past it.

What this category does well is restore output that has declined, typically from age, poor sleep, or chronic stress, back toward the range your body was designed to operate in. The 2007 Falutz trial in the New England Journal of Medicine, which studied Tesamorelin in HIV patients with visceral fat accumulation, found meaningful reductions in visceral adipose tissue and improvements in lipid markers, and that was within the limits of the body's own feedback system. The 2015 Stanley and Grinspoon review confirmed these effects across multiple human studies. The point is that working within the feedback loop is not a compromise, it is appropriate if restoration is the actual goal.

The second category is exogenous growth hormone, which is pharmaceutical HGH injected directly. When you introduce growth hormone from outside the body, you skip the pituitary entirely. The liver still sees the signal, still converts it to IGF-1, but the production was not initiated by the pituitary responding to GHRH. It came from the injection. This means somatostatin can rise, the pituitary can be suppressed, and the system can try to pump the brakes, but the growth hormone is already there regardless. The 1986 Rosenthal study showed that exogenous growth hormone directly inhibits GHRH-stimulated GH secretion in normal men, and the 2000 Hashimoto data showed that even the 20K isoform of exogenous GH suppresses endogenous 22K secretion. So when you are running pharmaceutical HGH, your pituitary is being told to stand down.

This is why stacking a GHRH analog on top of exogenous HGH does not do what most people assume. The pituitary is already suppressed by negative feedback from the elevated IGF-1 and from the exogenous GH itself, so the peptide is sending a signal into a system that is no longer listening. You are paying for a signal that gets ignored.

The third category is IGF-1 LR3, which skips the pituitary and the liver both. You are not stimulating growth hormone production, you are not waiting for hepatic conversion, you are injecting the downstream signaling molecule directly into circulation. This produces the fastest and most pronounced acute effect, but the tradeoff is receptor desensitization. Something called downregulation occurs when receptors are exposed to a ligand continuously, which means the cells reduce the number of available binding sites as a protective response, and the same dose produces progressively less effect. This is why IGF-1 LR3 has to be cycled, typically six to eight weeks, and then discontinued to allow receptor sensitivity to recover. The 1998 Chapman study demonstrated that free IGF-1, the unbound fraction circulating in plasma, is the primary driver of somatotroph suppression, meaning elevated IGF-1 from any source, including direct injection, feeds back to suppress the axis.

Now the visceral fat question, because this is where a lot of the confusion lives.

Tesamorelin gets marketed specifically as a visceral fat peptide, and some people believe it has a unique mechanism that the other compounds do not. What is true is that the clinical trials for Tesamorelin specifically measured visceral adipose tissue, and they found real reductions. What is not accurate is the implication that this makes Tesamorelin uniquely targeted to visceral fat in a way other GH-stimulating compounds are not.

Growth hormone drives fat mobilization by activating something called hormone-sensitive lipase, which breaks down stored triglycerides inside fat cells into free fatty acids that can be released and burned. The depot that responds most strongly to this signal is visceral fat, because visceral adipocytes have a higher density of GH receptors than subcutaneous fat. The 1997 Johannsson trial, which used pharmaceutical HGH rather than Tesamorelin, showed significant reductions in abdominal fat mass in obese men over six months. The mechanism is growth hormone acting on GH receptors in visceral fat. Whether the growth hormone came from a GHRH analog, exogenous HGH, or any other route, the downstream effect on visceral fat is driven by the same biology.

One practical point that applies across all three categories: none of this produces meaningful fat loss outside of a calorie deficit. Growth hormone increases the rate of fat mobilization, meaning it makes it easier for the body to access stored fat as fuel, but if energy intake exceeds energy expenditure, mobilized fatty acids get re-esterified and stored again. The Moller and Jorgensen 2009 review in Endocrine Reviews covers the full picture of GH effects on lipid metabolism, and the message is consistent. GH facilitates fat use, it does not override energy balance.

Most people chasing the "best" GH compound are solving for the wrong variable. The question is not which compound is most powerful in isolation. The question is where in the system the intervention needs to happen, and that answer is determined entirely by what is already going on with your own output. Restoring a deficient system from the top is a different problem than pushing a functioning system past its ceiling, and treating them as versions of the same problem is why so many stacking protocols produce mediocre results at significant cost.

The compound that fits your physiology at this moment is the right one. That is the whole decision.

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References

1. Falutz J, Allas S, Blot K, Potvin D, Kotler D, Somero M, Berger D, Brown S, Richmond G, Fessel J, Turner R, Grinspoon S. (2007). Metabolic effects of a growth hormone-releasing factor in patients with HIV. N Engl J Med 357(23):2359-70. DOI: 10.1056/NEJMoa072375
2. Stanley TL, Grinspoon SK. (2015). Effects of growth hormone-releasing hormone on visceral fat, metabolic, and cardiovascular indices in human studies. Growth Horm IGF Res 25(2):59-65. DOI: 10.1016/j.ghir.2014.12.005
3. Moller N, Jorgensen JO. (2009). Effects of growth hormone on glucose, lipid, and protein metabolism in human subjects. Endocr Rev 30(2):152-77. DOI: 10.1210/er.2008-0027
4. Hashimoto Y, Kamioka T, Hosaka M, Mabuchi K, Mizuchi A, Shimazaki Y, Tsunoo M, Tanaka T. (2000). Exogenous 20K growth hormone (GH) suppresses endogenous 22K GH secretion in normal men. J Clin Endocrinol Metab 85(2):601-6. DOI: 10.1210/jcem.85.2.6377
5. Rosenthal SM, Hulse JA, Kaplan SL, Grumbach MM. (1986). Exogenous growth hormone inhibits growth hormone-releasing factor-induced growth hormone secretion in normal men. J Clin Invest 77(1):176-83. DOI: 10.1172/JCI112273
6. Chapman IM, Hartman ML, Pieper KS, Skiles EH, Pezzoli SS, Hintz RL, Thorner MO. (1998). Recovery of growth hormone release from suppression by exogenous insulin-like growth factor I: evidence for a suppressive action of free rather than bound IGF-I. J Clin Endocrinol Metab 83(8):2836-42. DOI: 10.1210/jcem.83.8.5040
7. Johannsson G, Marin P, Lonn L, Ottosson M, Stenlof K, Bjorntorp P, Sjostrom L, Bengtsson BA. (1997). Growth hormone treatment of abdominally obese men reduces abdominal fat mass, improves glucose and lipoprotein metabolism, and reduces diastolic blood pressure. J Clin Endocrinol Metab 82(3):727-34. DOI: 10.1210/jcem.82.3.3809

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