Peptide Injections on the Rise; Doctors Alarmed at Side Effects Business Insider Can you inject peptides into the knee? Oral vs Injectable BPC 157: Differences, Benefits, and When to Use Eac Revolution Health & Wellness Still injecting in the same spot every time? Read this. Where you inject your peptides can actually affect absorption, comfort, and results. Quick guide: Abdomen: fastest absorption Upper arms Subcutaneous injection: Definition and what to expect Subcutaneous Injections: Where and How To Give