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: What It Is and How to Give One Uses and Benefits #ghk GHK Cu is a naturally occurring peptide in human plasma that declines with age. When used in injections (usually subcutaneous), it can offer various benefits: Skin Rejuvenation and Anti Aging: Amazon.com: GHK Cu Copper Peptide Supplement, Anti Aging & Hair Growth Support, Improves Skin Elasticity & Firmness, Thicker, Fuller Hair, Easy Absorption, Precisely Dosed, 90 Vegan Capsules : Health & Household 7% GHK CU ACCELERANT Platinum Skin Care