Most of the stuff on the market these days is just packed with caffine instead of ephedra. So it's just like drinking coffee in when you take it. The purpose (as I'm sure you know) is to artifically increase your metabolism so you burn more calories.
Well, if you reach a desired weight for example and suddenly go off your thermogenic of choice, you also need to decrease your total caloric intake to match. Otherwise, you'll just put weight back on.
Also, another thing to keep in mind is that your body will develop a resistance to any product over time. So when you start off taking 1 capsule of Hydroxicut your body will acclimate itself to this increased level of caffine over the period of a week or two and then you'll have to increase your dosage to continue to see effects.