Losing weight through any method will make your metabolism slow down - fat is metabolically active. Uncouplers won't change this. Even if 100% of your weight loss is fat, your BMR is going to drop. The amount of metabolic adaptation from caloric deficits is grossly overstated by many people, and the "starvation mode" adaptation is temporary. Just reaching a maintenance level of calories for a relatively short period of time is enough to reset it - but this change is minor to begin with. The majority of any metabolism slowing will occur purely as a function of weight loss.

The issue with regaining weight after coming off these drugs is that people don't change their habits, and once they are off, they no longer have the limited appetite, and return to eating like they did before, which just results in the problem reoccurring. Uncouplers won't change this.

If people want to sustain their weight loss, they either need to change their lifestyle and eating habits, or they need to stay on the drugs, and potentially even both.