I used Cleanwhites Teeth Whiting System for a month before giving up on it. I've never had brown teeth, but my teeth have never been a perfect white either. Throughout the time that I used this product, my teeth only lightened about a shade whiter. The strips would constantly fall off my teeth. Whether they were sliding down, pulling to one side, or rising into my gums, they just would not stick. The taste of the whitening gel is bad enough to make me sick it is so disgusting. Make sure you do not move your tongue around at all while using this product or you will have the horrible taste in you mouth for the whole 30 minutes. I've never had teeth sensitivity, but while using this product, my gums would get sore and my teeth would hurt while eating hot and cold foods. In the time that it takes to whiten you teeth and considering the drawbacks, this product is just not worth it.