Peptide cycling means taking a compound for a defined period (e.g., 8 weeks on) followed by an off period (e.g., 4 weeks off). Cycling is used for GH-secretagogues and IGF-1 analogs to prevent receptor downregulation. It's NOT used for chronic conditions where the goal is stable serum levels (GLP-1s, FDA-approved tesamorelin for HIV lipodystrophy). The Stack Builder supports modeling cycles in multi-week schedules.