I cannot answer if it is the "most" effective cream for wrinkles because every cream reacts differently for each individual and results vary. However, Retin A is one of the most effective topical creams for photoaging, i.e. aging as a result of sun damage.
The reason why most dermatologists recommend Retin A is because it has 20 years of good science behind it to show it does actually make a difference whereas so many other creams and potions on the market have no comparable peer reviewed studies to back them up. The science behind Retin A has been validated.
That being said, it works slowly, and has side effects so I would recommend discussing with your dermatologist before starting Retin A.



