Teprenone is the brand name for a drug known as geranylgeranylacetone, which is used to treat gastric ulcers and is being researched as an option for slowing age-related hearing loss (Sources: Brain Research, May 2008, pages 9–17; and Digestion, October 2007, pages 215–224). What do hearing loss and ulcers have to do with aging skin? One of the key ways geranylgeranylacetone works is by influencing heat-shock proteins, which help other proteins interact as they should at the cellular level, which in turn affects many systems in the body. Heat-shock proteins are most active during times of stress, such as exposure to cigarette smoke and exposure to sunlight.
When heat-shock proteins are reduced (which ultimately is what you want because that means reducing skin inflammation—think inflamm-aging), cells appear to live longer. Some cosmetic companies have theorized that geranylgeranylacetone (as Teprenone) also may have a helpful effect when applied topically. Perhaps their logic went something like this: The skin is the body’s largest organ, it produces a lot of heat-shock proteins because it is exposed to environmental and physical stresses, so ingredients that help reduce these damaging proteins will be of benefit.
The problem? There’s no research that topically applied geranylgeranylacetone has any effect on heat-shock proteins in skin. Moreover, any cosmetic company whose products contain teprenone means they're using a drug ingredient in a cosmetic product, so the consumer is the guinea pig.