Herbal remedies or as they could have been called "gaia medicines / remedies / treatments", were probably hit and miss at best.
Rubbing concoctions containing some kind of mashed or ground leaves onto skin, or chewing bits of plant matter, as ways to alieviate or cure what ailed you, were always going to be hit and miss really, because humankind had no basis of fact or statistical analysis to work with, so it was trial and error and probably sometimes collateral damage, when people now and again ate something poisonous.
People may have benefitted from such gaia medicines, but even then benefit could have been reletively mild or barely even noticable. Whether the efforts from witch doctors, faired any better medicinally than western medicines, is probably difficult to ascertain, although such medicines do continue to be used by such medics of type today, in some african countries.
However Herbal remedies now in the form of slimming products are just plain crappy, simple as. Unless you actually take the pills and make no other changes to your life, you cannot isolate the effects on weight loss.