Whitestrips work well, but most people should expect to go through 3-4 boxes to get optimum results. Using tooth whiteners causes sensitivity in alot of people, and is the biggest drawback of using them. No matter how often someone brushes their teeth it's still possible for them to discolor, there are many other factors that affect the tooth color besides hygeine. I recommend the professional Whitestrips which you can get from your dentist. If you don't like the strips and find that they fall off or make you drool or what not. your dentist can make a bleaching tray for you and you can use another whitening system. Also you have to be reasonable with your expectations, if you're teeth are already pretty white you will not go to gleeming white. People with the best results usually are people who have teeth with lots of yellow stains from smoking and drinking coffee.