Strangely enough, you don't really need pills to lose excess weight. You can lose excess water weight (fluid retention) simply by avoiding eating salt/sodium and salty food and making sure you eat plenty of fruit and unsalted vegetables, and you can reduce excess fat (fat retention) by making sure you have plenty of dairy calcium (and vitamin D) and other minerals.
Obesity and the Salt Connection
prescribed steroids and HRT
See Sodium in foods
and FAT RETENTION
But if you are VERY overweight and water-logged because of taking prescribed steroids (like prednisone and prednisolone and HRT) or prescribed antidepressants (like, notoriously, amitriptyline) or other dangerous prescription drugs, then you may feel you need a bit of pharmaceutical help. In this case, the correct therapy is a thiazide diuretic like bendrofluazide/bendroflumethiazide in low dose. This has the same effect as lowering salt intake, because it removes sodium and water from the body. Unfortunately it also has the undesirable effect of removing potassium from the body, so it is not as safe as simply cutting out salt, and high dose is certainly not a good idea. But it is much safer than most pharmaceutical drugs and it certainly removes excess water which is the primary cause of the overweight and it lowers high blood pressure and has other good effects.