Here is a quick overview of the 4 primary Growth Hormone Releasing Peptides most commonly used i athleti pursuits today. This is meant as a means to determine what might be the best and most appropriate application for your individual research needs.
HEXARELIN
Hexarelin is in the category of drugs known as GH secretagogues. This category of drugs includes GHRP-2, GHRP-6, Ipamorelin, and Hexarelin. Its primary function is to stimulate the pituitary gland to produce more growth hormone. Like the other GHRPs, it has a 2-fold mechanism of action, in that it causes an increase in GH through amplifying the natural growth hormone releasing hormone (GHRH) signal transduction pathway, as well as by suppressing the actions of Somatostatin.
Hexarelin, on a mcg per mcg basis, is the most potent of the GHRP’s for GH release. However, Hexarelin administration will quickly lead to desensitization when used at effective dosages, which makes it less than ideal for long-term use. This limitation has led to a decrease in popularity among users of GH peptides, with GHRP-2 and Ipamorelin leading the pack in the area of long-term effectiveness. However, these limitations do not mean Hexarelin is worthless. On the contrary, Hexarelin can be added to other GHRP’s (such as GHRP-2 & Ipamorelin) in lower dosages, in order to elicit further elevations in GH without incurring the desensitization that commonly presents itself when using Hex alone at peak effective dosages.
Common benefits of GH (Hexarelin) include: 
Decreases in body fat
An increase in lean mass
Increased collagen production
Improved sleep
Increased cellular repair
An increase in IGF-1
Increases in bone density
Common side effects of GH (Hexarelin) include:
Water retention
Tightness and/or carpel tunnel-like symptoms
Numbness and tingling in the extremities
A decrease in insulin sensitivity
Tiredness
http://www.evolutionpeptides.com/product.aspx?id=9&cat=1
IPAMORELIN
Ipamorelin is in the category of drugs known as GH secretagogues. This category of drugs includes GHRP-2, GHRP-6, Ipamorelin, and Hexarelin. Its primary function is to stimulate the pituitary gland to produce more growth hormone. Like the other GHRPs, it has a 2-fold mechanism of action, in that it causes an increase in GH through amplifying the natural growth hormone releasing hormone (GHRH) signal transduction pathway, as well as by suppressing the actions of Somatostatin.
Ipamorelin is a 3rd generation GHRP which displays great selectivity in its actions. Ipamorelin will not lead to any degree of appetite stimulation, will not affect prolactin or cortisol, and is used solely for GH release. On a mcg to mcg basis, its strength is comparable to GHRP-6, but unlike GHRP-6, it can be dosed much higher, resulting in potentially greater elevations in GH. Similar to GHRP-2, IPA has no ceiling dose. Therefore, as the dosage of IPA is titrated upward, GH release will continue to rise accordingly. Ipamorelin has developed a reputation as the “cleanest” of the GHRP’s and rightfully so.
Common benefits of GH (Ipamorelin) include: 
Decreases in body fat
An increase in lean mass
Increased collagen production
Improved sleep
Increased cellular repair
An increase in IGF-1
Increases in bone density
Common side effects of GH (Ipamorelin) include:
Water retention
Tightness and/or carpel tunnel-like symptoms
Numbness and tingling in the extremities
A decrease in insulin sensitivity
Tiredness
http://www.evolutionpeptides.com/product.aspx?id=8&cat=1
GHRP-2
Growth hormone releasing peptide-2 (GHRP-2) is in the category of drugs known as GH secretagogues. This category of drugs includes GHRP-2, GHRP-6, Ipamorelin, and Hexarelin. Their primary function is to stimulate the pituitary gland to produce more growth hormone. GHRPs have a 2-fold mechanism of action, in that they cause an increase in GH through amplifying the natural growth hormone releasing hormone (GHRH) signal transduction pathway, as well as by suppressing the actions of somatostatin.
GHRP-2 is a 2nd generation GHRP and finds its primary use in the area of GH release. It is superior to GHRP-6 in this regard and is currently the preferred peptide for attaining maximum elevations in GH over the long-term. Recent research also reveals that GHRP-2 can be dosed much higher than initially thought, while avoiding the desensitization that is inherent in some of our other GHRP’s. This provides the user with the opportunity to experience greater elevations in total GH, depending on the dosage administered. Lastly, while GHRP-2 can potentially lead to some degree appetite stimulation, not all users experience this effect and when they do, it is typically much less profound in comparison to GHRP-6.
Common benefits of GH (GHRP-2) include:
Decreases in body fat
An increase in lean mass
Increased collagen production
Improved sleep
Increased cellular repair
An increase in IGF-1
Increases in bone density
Common side effects of GH (GHRP-2) include:
Water retention
Tightness and/or carpel tunnel-like symptoms
Numbness and tingling in the extremities
A decrease insulin sensitivity
Tiredness
http://www.evolutionpeptides.com/product.aspx?id=6&cat=1
GHRP-6
Growth hormone releasing peptide-6 (GHRP-6) is in the category of drugs known as GH Secretagogues. This category of drugs includes GHRP-2, GHRP-6, Ipamorelin, and Hexarelin. Their primary function is to stimulate the pituitary gland to produce more Growth Hormone. GHRPs have a 2-fold mechanism of action, in that they cause an increase in GH through amplifying the natural growth hormone releasing hormone (GHRH) signal transduction pathway, as well as by suppressing the actions of somatostatin.
GHRP-6 is a 1st generation GHRP and is primarily used in the research community for two reasons, which are 1) GH release and 2) Appetite stimulation. If researching this peptide for GH release, the researcher should consider whether or not the accompanying appetite stimulation is a beneficial or negative characteristic in their current circumstances. In researchers who struggle with appetite issues and have trouble eating enough food to meet their daily caloric requirements, this peptide can prove to be a great addition to their program. For those on contest diets or who are trying to lean out, they may want to forego this peptide in exchange for a GHRP absent of this effect.
Common benefits of GH (GHRP-6) include:
Reductions in body fat
Increased lean mass.
Increased collagen production
Improved sleep
Increased cellular repair
An increase in IGF-1
Increases in bone density
Common side effects of GH (GHRP-6) include:
Water retention
Tightness and/or carpel tunnel-like symptoms in the wrist/hand.
Numbness and tingling in the extremities
A decrease in insulin sensitivity
Tiredness
http://www.evolutionpeptides.com/product.aspx?id=7&cat=1
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