How Does Ipamorelin Affect Growth Hormone?


Ipamorelin is a synthetic agonist of the ghrelin receptor and ghrelin is often referred to as the hunger hormone. Higher levels of ghrelin receptor activation lead to increased appetite, but they also lead to increased growth and changes in energy metabolism. How does ipamorelin create its effects?

Ipamorelin and Ghrelin

Ipamorelin is a five-amino-acid protein (Aib-His-D-2-Nal-D-Phe-Lys-NH2) derived from growth hormone releasing peptide-1 (another agonist of the ghrelin receptor). It was originally developed to aid in treatment of postoperative ileus (slow movement of food through the intestine after surgery), but has since been investigated as a potential growth hormone stimulant and for its beneficial effects on cardiovascular and cognitive function.

Ipamorelin can be thought of as a synthetic form of ghrelin. Ghrelin (lenomorlin) is a naturally occurring protein produced by specific cells in the gastrointestinal (GI) tract. Though produced in the GI tract, ghrelin activates receptors in the central nervous system to stimulate hunger and regulate the distribution and rate of use of energy throughout the body. When the stomach is empty, ghrelin is secreted, reaching its highest levels just before eating. The best way to think of ghrelin is as a preparatory hormone. It gets the body ready for food intake and part of that function is to increase release of growth hormone so that the body is prepared to make use of the energy that will be consumed in the form of food.

Ipamorelin and Growth Hormone

Ipamorelin causes growth hormone release, but unlike ghrelin it does not have a massive effect on hunger. In fact, ipamorelin is almost exclusively a growth-hormone secretagogue1 . Synthetic molecules like ipamorelin (e.g. pralmorelin, GHRP-6) have been developed in the past. Studies have shown them to have a diverse range of effects that include
. Increasing hunger,
. Increasing prolactin release,
. Increasing follicle-stimulating hormone levels,
. Increasing luteinizing hormone levels, and
. Increasing thyroid-stimulating hormone levels.

The problem with producing such diverse effects is that synthetic analogues of ghrelin can have a profound impact on sex hormones and secondary sex characteristics as well as deleterious effects on cortisol levels, cardiovascular health, and immune function. Because ipamorelin is so selective, it has none of the above side effects. In fact, it may improve cardiovascular function along with other physiologic parameters.

Ipamorelin and other growth hormone secretagogues do not act on the growth hormone secreting hormone receptor, which means they have a very distinct functional difference from growth hormone releasing hormone (GHRH) and its synthetic analogues (i.e. GRF (1-29), CJC-1295, etc.). This is important because it means that growth hormone secretagogues are synergistic with GHRH analogues. When taken together, the effect is a massive increase in growth hormone release2.

Ipamorelin also shows less response to standard growth hormone regulation. The effects of GHRH can be almost abolished by somatostatin, a natural inhibitor of growth hormone release, as well as by increased glucose levels, increased fatty acid levels, glucocorticoids, and increased levels of growth hormone itself. While there is a small effect of these substances on GH release secondary to ipamorelin, it orders of magnitude smaller than the inhibitory effect that they have on GHRH3.


Ipamorelin Administration

One of the interesting benefits of ipamorelin and other growth hormone secretagogues is that they easily cross both intestinal and blood-brain barriers. This means that these peptides can be administered orally, reducing the need for injections and the risks (primarily infection) associated with them4. Human and animal studies show that orally administered GHRP-6, which is similar to ipamorelin, causes growth hormone levels to start to rise after just fifteen minutes and leads to peak activity in just sixty minutes5. Investigations into intravenous, subcutaneous, oral, and intranasal administration of ipamorelin are ongoing. Need more information? visit


1. Raun, K. et al. Ipamorelin, the first selective growth hormone secretagogue. Eur. J. Endocrinol. Eur. Fed. Endocr. Soc.139, 552-561 (1998).

2. Camanni, F., Ghigo, E. & Arvat, E. Growth hormone-releasing peptides and their analogs. Front. Neuroendocrinol.19, 47-72 (1998).

3. Ghigo, E., Arvat, E., Muccioli, G. & Camanni, F. Growth hormone-releasing peptides. Eur. J. Endocrinol. Eur. Fed. Endocr. Soc.136, 445-460 (1997).

4. Ghigo, E., Arvat, E. & Camanni, F. Orally active growth hormone secretagogues: state of the art and clinical perspectives. Ann. Med.30, 159-168 (1998).

5. Argente, J., García-Segura, L. M., Pozo, J. & Chowen, J. A. Growth hormone-releasing peptides: clinical and basic aspects. Horm. Res.46, 155-159 (1996).

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