The tissue layer just beneath the skin — where most research peptides are injected, using a short needle at approximately a 45-degree angle.Subcutaneous injection delivers the compound into the fat and connective tissue between skin and muscle, where it is absorbed via local capillaries and lymphatic vessels. Absorption is slower and more sustained than intramuscular injection. Common SC injection sites: abdomen (preferred — consistent absorption), lateral thigh, outer upper arm. Rotate sites to prevent lipodystrophy. SC needles are typically 25–31 gauge, 8–12mm length.