A newer non-prescription substance for the treatment of melasma (also refered to as hyperpigmentation) is N-acetyl glucosamine, which becomes more effective when combined with niacinamide. This combination is found in the Oil of Olay Definity line of products.
Just before Definity was released, I read an excerpt of research indicating that topical N-acetyl glucosamine reduced hyperpigmentation. Shortly after, a study of combining N-acetyl glucosamine with niacinamide, the combination found in Definity, was shown to reduce hyperpigmentation even more effectively. Proctor and Gamble, the parent company of Olay was involved in the study.
When I did a search for products with the combination, Definity was brand new and was the only product I found at that time containing both N-acytyl glucosamine and niacinamide. Since then, numerous skin lightening products have began to add either glucosamine alone or N-acetyl glucosamine, but I still find a lack of products that include the niacinamide. So, I purchased the Definity night creme and have gone through a couple jars of it now.
My experience using Definity for approximately the past 12-14 weeks has been pretty good. I have mild hyperpigmentation along my jaw line and have seen some dramatic lightening of the areas over the past few months. However, I have been using a fairly aggressive melasma treatment program that includes other products, particularly my favorite PCA Skin Care Phaze 13. It is also winter and so my skin is seeing less sun. That makes it difficult to point to one single product or factor for my recent improvement.
Regardless, unlike some substances and products, the positive effects of the glucosamine complex is documented through scientific study. Further, unlike many melasma treatments, there are generally no side effects. So while one might pause before putting products such as hydroquinone, Retin-A, or various alpha hydroxy acids on their face, especially it the skin is sensitive, absent an unusual allergy or sensitivity, trying Oil of Olay Definity can't really hurt.
The only downside of using Definity for me is that, at this time of year, I don't find it moisturizing enough. Although labeled as a creme, I find it to be closer in consistency and behavior to a lotion. It is not a thick as say, Estee Lauder Daywear, and it spreads thin pretty fast. But I am feeling unusually dry this winter, and suspect when the weather warms up, it will be just fine for me. For now, I use it on the hyperpigmented areas, and then use an additional moisturizer on top of it.