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 7% GHK CU ACCELERANT Platinum Skin Care Buy GHK Cu 50 mg Peptide (Research Grade) 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 Subcutaneous Injection: What It Is and How to Give One