Find the strongest over-the-counter Retinol at Amazon.com, which offers several types of the product with a 2-percent concentration. This is the highest concentration available in over-the-counter form, according to Amazon.com.
As of 2015, Amazon.com users give the products NCN Skincare Retinol 2.0% and Watts Beauty 2% Retinol Serum 4 out of a possible 5 stars each. Amazon.com users report their skin feeling and looking tighter and younger after using both products regularly. Although these products are available over the counter, product warnings state that a doctor should be consulted before use if you are pregnant. They also state that Retinol can cause skin irritation, especially at higher concentrations, and should therefore be used with caution.