Half-Life
The time it takes for the concentration of a compound in the body to decrease by half, determining how frequently it needs to be dosed.
Half-life is one of the most important pharmacokinetic properties of any peptide or compound. A peptide with a 30-minute half-life will have half its peak concentration remaining after 30 minutes, a quarter remaining after 60 minutes, and so on — it is effectively cleared within 4–5 half-lives.
Short half-lives (common among GHRPs and GHRHs) require multiple daily injections to maintain stable blood levels. Longer half-life analogs are often preferred for convenience. Half-life is distinct from duration of effect — some compounds have downstream effects (like elevated IGF-1) that outlast their plasma half-life significantly.