A stack is a combination of peptides used together — for example, BPC-157 + TB-500 for tendon healing, or CJC-1295 + Ipamorelin for nighttime GH pulse. Some stacks are well-trialed combinations (cagrilintide + semaglutide); others are community-experimental. The Stack Builder on this site lets you model stacks and flags mechanism overlap (e.g., 'don't stack two GLP-1s — pick one').