Obagi-C Rx System for Normal to Oily Skin—Remarkable Results in Just 6 Weeks. In a clinical trial composed of subjects of varying ages and skin types, the Obagi-C Rx System for Normal to Oily Skin showed visible results in only 6 weeks when applied as directed. Some of the results you might expect from daily use of your Obagi-C Rx System include improved appearance of hyperpigmentation (discoloration), as well as restored balance and clarity to lackluster skin