It can be tempting to skip straight to a higher retinol concentration, to get more bang for your buck, as it were. But, Dr Hudson-Peacock tells us, "I prefer to recommend Medik8 Retinol 3TR (£29), the lowest strength in the line. I then advise stepping up depending on tolerability when a replacement is needed." So, start with the 3TR, then once you run out, look to step up to the 3TR Intense or go straight to the 6TR.