Borrowed from Datbtrue
We need only to examine the results of the normal test subjects from three oft-cited studies that established the relevant protocol.
In the first study "Inhibition of growth hormone release after the combined administration of GHRH and GHRP-6 in patients with Cushing's syndrome", Alfonso Leal-Cerro..., Clinical Endocrinology 1994, 41 (5) , 649–654, three different peptide/peptide combinations were used.
GHRH was administered alone at 100mcg. This resulted in area under the curve (AUC) measured for 120 minutes of GH secretion of 1420 ± 330.
GHRP-6 was administered alone at 100mcg. This resulted in area under the curve (AUC) measured for 120 minutes of GH secretion of 2278 ± 290.
GHRH plus GHRP-6 was administered together at 100mcg each. This resulted in area under the curve (AUC) measured for 120 minutes of GH secretion of 7332 ± 592.
As a single dose these results show that GHRP-6 is about twice as effective as GHRH.
The synergy between GHRH & GHRP-6 is clearly evident as co-administration resulted in twice the benefit of the additive values of single doses of the two peptides.
The second study is the one that established the saturation dose for these peptides often used in other studies. "Growth hormone (GH)-releasing peptide stimulates GH release in normal men and acts synergistically with GH-releasing hormone ", CY Bowers..., J. Clin. Endocrinol. Metab., Apr 1990; 70: 975-982.
In that study GHRH at a dose of 1.0 microgram/kg was administered alone and then together with various doses of GHRP-6 (0.1, 0.3, and 1.0 microgram/kg). They found that the submaximal dosages of 0.1 and 0.3 microgram/kg GHRP-6 plus 1 microgram/kg GHRH did have the effect of stimulating GH release synergistically.
However the larger dose of 1 mcg/kg of GHRP-6 was found to be the saturation dose when used in combination w/ 1 mcg/kg of GHRH.
It is also noteworthy that serum prolactin and cortisol levels rose about 2-fold above base levels only at the 1 microgram/kg dose of GHRP-6 and not at the submaximal dosages.
The final study, "Preserved Growth Hormone (GH) Secretion in Aged and Very Old Subjects after Testing with the Combined Stimulus GH-Releasing Hormone plus GH-Releasing Hexapeptide-6", Micic D..., J Clin Endocrinol Metab. 1998 Jul;83(7):2569-72 is fascinating for several reasons.
By reference to citation it is noted that "GHRH plus GHRP-6 (both at saturating dose) is nowadays considered the most potent stimulus of GH secretion in man being able to restore the GH secretion in states associated with chronic blockade of somatotroph activity (as in obesity)...it elicits a near-normal GH discharge in obesity, in patients with hypothyroidism and in patients with type 2 diabetes mellitus."
This particular study examined the effects of combined administration of GHRH, immediately followed by GHRP-6 in a group of very old subjects (age higher than 75 yr), as compared with both normal adults (less than 40 yr) and aged subjects (age 46–65 yr). The dosing levels used were 90mcg of GHRH followed by 1mcg/kg of GHRP-6.
All the subjects had a positive GH secretory response to the combined administration with no differences observed between men and women. However the group comprising the very old had the highest level of GH release followed by the group comprising the aged subjects with the "less than 40 yr group" experiencing a substantial rise but not as high as the other two groups.
The study concluded that the lack of side-effects & safety of the protocol and the discovered lack of age-related decline in the "GHRH-GHRP-6-mediated GH release opens the possibility of using it as a therapeutical tool to revert some deleterious manifestations of aging in man."
. Just showing the new guy how things roll around here. 
