For subcutaneous injections, using shorter needles (4 5mm) is the safest choice to ensure medication stays in the fatty layer and avoids muscle injury. A 4mm needle is ideal, minimizing pain while keeping Subcutaneous Injection Sites and Instructions for Safe Self Administration GHK Cu Peptide: What It Does for Body Composition and Metabolic Health 7.4 Subcutaneous Injections Clinical Procedures for Safer Patient Care Glow Peptide Protocol GHK Cu, BPC 157, TB 500 Neurogan Health The GHK Cu pen works. But needles at home were never the answer. We took the same clinically backed copper peptide complex and put it into a serum you can use in 30 seconds,