Yes, they will give you a boost, but usually they will have unpleasant side effects, that are usually what helps you with the weight loss in the first place. The most common of those is diarrhea, because many work by partially blocking fat absorption- and if it's not absorbed, it needs to come out somehow. Herbal mixes and pills on the other hand, tend to act as a diuretic- you'll be running to the toilet every ten minutes to pee- this is especially true for teas, though I think a big part of that might be the sharp increase in the amount of liquids you take in. In any case, you really shouldn't use them unless you are extremely obese and are willing to suffer to decrease your health risk a bit, because the results may be extremely embarrassing, disruptive, and generally bad for your body. On the other hand, you might want to get a cleanse kit from a local health products store- their mixes tend to be less harmful, and if you do a cleanse before a diet, your intestines will work better, and you'll feel better and have more energy. If you do that, consult the store manager to see if you can talk to someone that tried that particular cleanse kit before, for tips on that particular kit.