This product definitely whitens teeth, but I didn't finish using the whole box because my teeth became extremely sensitive to the point it sometimes made me cringe (especially to cold things). Even without finishing the whole pack, my teeth had already reached the whiteness that I was aiming for. I used this product years ago, and I'd say the color of my teeth lasted at least 4 years before I felt like I needed to whiten them again ( it also helps that I don't drink regularly drink coffee or tea, and don't smoke). Since it works so well, I might consider using this product again, but the sensitivity pain is off-putting. I would recommend researching reviews for newer versions of this product to see if they've improved upon it.