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 GHK Cu vs NAD+: Which Longevity Peptide Should You Take or Stack? GHK Cu Copper Peptide Benefits, Uses & Safety Intra V In Vitro and in Vivo Studies of pH Sensitive GHK Cu Incorporated Polyaspartic and Polyacrylic Acid Superabsorbent Polymer ACS Omega Subcutaneous Injection: What It Is and How to Give One