Swallow a pill. It inflates into a balloon. You're full for four months. (Eat less = lose weight). Balloon deflates and you excrete it.
It's not available (yet) in the US but Allurion, a Boston-based startup had just gained an additional $27 million in funding to pursue FDA approval. If you're in France, Spain, Belgium, and some other European or Middle East countries it's already available.
There's a lot of competition around gastric bypass using implantable devices, but they're most often surgical. This one's not. You swallow the pill portion, it's filled with up to 550ml over the next ten minutes, then the catheter's detached and pulled out. (Might be fighting a gag reflex here.) that's pretty much it. The "Elipse Balloon" persists in the stomach for the next four months before it deflates and is passed.
Allurion has a rival in the US with a similar balloon-in-a-pill company Obalon which has already met FDA approval. (The main difference seems to be that Obalon requires endoscopic removal of the balloon which will greatly reduce market acceptance.)
Here's a video of the Obalon Ballon in action
If Allurion is successful in the US of obtaining FDA approval as simply a weight loss device they could be adopted by cosmetic practices as a vanity treatment. (If they're only approved for the very obese the aesthetics market probably won't have nearly the penetration.