GH-releasing peptides (GHRPs and GHRHs) are strongly inhibited by insulin. Administering them in the post-workout window — when carbohydrate intake spikes insulin — significantly blunts the GH pulse they would otherwise produce. Timing these peptides in a fasted or low-insulin state is essential for efficacy.
How does insulin antagonise GH peptide activity?
GH secretion is subject to somatostatin inhibition, and insulin elevation increases somatostatin tone. GH-releasing peptides work by suppressing somatostatin and stimulating the pituitary, but elevated insulin partially overrides this mechanism. Studies show GH pulse amplitude is reduced by 30–60% when GHRPs are administered alongside carbohydrate feeding compared to fasted administration.
What is the optimal timing window for GH peptides around training?
Pre-workout fasted administration (60+ minutes before eating) or pre-sleep administration (3+ hours after the last meal) are the two windows with the lowest insulin interference. Pre-sleep is generally considered the more practical and effective window — it coincides with the natural nocturnal GH pulse and requires no alteration of post-workout nutrition, which matters for muscle protein synthesis.