Sensa has been charged by the FDA on false advertising. There's no such thing as a miracle weight loss method. The closest you can get is a good guide like this http://goo.gl/kiG7BE and avoiding drugs like Sensa who can have some pretty nasty side effects in the long run.
Sensa can be found in local pharmacies or in the drug sections of department stores. Wal-Mart carries Sensa. Most of these over the counter products do not work. The only approved diet medication over the counter is Alli. It as been doctor tested and can be effective used with a proper diet.