Half-life (t½) is how long it takes for the body to clear half of the administered dose. It's the main driver of dosing frequency. Semaglutide's half-life is ~165 hours (a week) — that's why it's dosed weekly. CJC-1295 with DAC has a half-life of 6-8 days; without DAC it's about 30 minutes. Short half-life = frequent dosing or pulsatile delivery; long half-life = stable serum levels with weekly injections.