I’ve tried Alli and yes, it does work.
It’s a lipase inhibitor. Without lipase in your small intestine, fat cannot be broken down for digestion. So, it will come out the back door.
I’ll be honest, the “treatment” effects can be really yucky. What Alli does is “classical conditioning.” You can’t eat crappy, fatty foods with Alli, you’re basically forced into eating healthy, low-fat foods or suffer the ill effects.
If you can handle the treatment effects and are willing to change your diet (no relapses!) then Alli may work for you. But hey, I’m no doctor.