I've used Orlistat, but it's important to acknowledge that it's certainly not a magic cure. I started using Orlistat 6 months after I'd addressed my inactive lifestyle and decided that I need to really look at my diet to keep the losses going.
Because Orlistat works by preventing about 1/3 of the fat you eat from being absorbed by your body, your body still needs to excrete it. Depending on how much fat you've eaten, the "treatment effects" can be nothing, can be a softer stool, or can be very loose stools and oily leakage when you're not expecting it.
I found Orlistat helped to reinforce good habits for me. It made me eat only three times per day - no snacking - and I kept my fat intake per meal down to a maximum of 5 g. When you start looking at the labels on food, it's quite an eye-opener. So many things are utterly packed with unnecessary fat.
When I kept my meals to no more than 5g of fat, I had no "treatment effects". On the very rare occasion that I overindulged (say, a friend's birthday meal out) Orlistat worked as a bit of a safety net, but of course the unpleasant "treatment effects" followed!
It really isn't about calories in themselves, it's about the amount of fat in your diet.
Good luck!