SC vs IM
Two parenteral injection routes for peptides — SC into adipose tissue, IM into skeletal muscle — with distinct PK profiles.
For laboratory and research use only — not for human consumption.
Subcutaneous (SC) and intramuscular (IM) injection are the two principal parenteral routes used in peptide research. Subcutaneous injection deposits material into the loose connective tissue of the dermal-fat interface (commonly anterior abdomen, lateral thigh, or upper outer arm) using a 27–31 G needle 4–13 mm in length. Absorption is governed by local capillary perfusion and is generally slower and more sustained than IM, producing flatter plasma profiles ideal for peptides where Cmax is undesirable. Intramuscular injection deposits material into the body of a skeletal muscle (commonly vastus lateralis, deltoid, or gluteal) using a 22–25 G needle 25–38 mm in length. Absorption is faster due to denser vascularity and higher tissue blood flow, producing sharper plasma peaks. For most research peptides — BPC-157, TB-500, GHK-Cu, KPV, AOD-9604, AC-SDKP, sermorelin, ipamorelin — SC is the standard research route because it is technically simpler, less painful, lower in injection-site complication risk, and produces the more clinically relevant PK profile. IM is preferred for select compounds where rapid onset is required, for larger volumes (>1.5 mL is poorly tolerated SC), or where adipose-tissue retention complicates PK interpretation. Choice of route should be documented in any research protocol and is a recognised source of inter-study variability.