Medik8 C-Tetra is a revolutionary ultra-stable vitamin C serum which helps combat sun-induced damage to the skin, trigger collagen synthesis, increase the skin’s elasticity and density as well as improve the skin’s texture and brighten the complexion. Designed for both men and women in their mid-20s to 40s. Pro-Collagen Synthesis Super Antioxidant Serum. Medik8 C-Tetra is a revolutionary ultra-stable vitamin C serum which helps combat sun-induced damage to the skin, trigger collagen synthesis, increase the skin’s elasticity and density as well as improve the skin’s texture and brighten the complexion. Designed for both men and women in their mid-20s to 40s. Regular vitamin C is very unstable and many typical vitamin C products are inactive by the time they are used on the skin, in some cases, they have become pro-oxidant and actually generate free radicals! Ground-breaking stability data on C-Tetra guarantees real vitamin C activity and best of all, unlike L-ascorbic acid (regular