These medicine are of a class called GLP-1 receptor agonists. They work by mimicking the effect of GLP-1 which is endogenous to the body. Normally enzymes in your body break down and inactivate GLP-1, these drugs however stay in circulation for days.

They were developed for diabetes because they lower blood sugar levels by stimulating the release of insulin when you eat -the main function of your body’s own GLP-1. But they found weight loss at pretty high levels, which is good for people with type 2 diabetes.

The exact weight loss mechanism is unknown, as far as I’m aware, but we do know there are GLP-1 receptors in the brain, and it seems to regulate appetite. People that take these medicine just eat less, they are even reported to enjoy food less.

There are in fact other effective weight loss medicines (amphetamine -like substances) but they suffer from side effects. It’s always complicated with drugs that affect the brain. So far the GLP1 class of drugs seem relatively safe. But unregulated use because people want to lose weight quickly is a bad thing imo.