Half-life

Half-life is the time it takes for the concentration of a substance in the body to drop to half its peak value. It's a standard pharmacokinetic measure used to understand how frequently a compound needs to be administered to maintain consistent levels. For peptides, half-life is often short — unmodified peptides can be cleared in minutes to hours. This matters in practice because a compound with a 10-minute half-life needs to be administered very differently from one with a 6-day half-life. CJC-1295 illustrates the engineering response to this problem. The unmodified version (sometimes called Modified GRF 1-29) has a half-life of about 30 minutes. The DAC-modified version — CJC-1295 with Drug Affinity Complex — binds to plasma albumin, extending the half-life to approximately 6–8 days. That single modification changes the dosing from multiple times daily to once or twice weekly. Sermorelin, as a GHRH 1-29 fragment, has a short half-life (minutes) — which some researchers argue is an advantage, since it preserves the pulsatile pattern of natural GH release rather than producing sustained elevation. The debate between short half-life (physiological pulse) and long half-life (sustained elevation) runs through the GH secretagogue literature.