Bad. Or, rather, potentially-addictive, with bizarre and dangerous side-effects and the worst of it:
!!Even the really, really effective ones are not effective, really!! People who use them lose 1-2 pounds a month more than the control groups who are losing 3-6 pounds a month already. How is this the 'miracle of weight loss'?!?
There are a number of very effective weight-loss and appetite suppressant choices that are natural and healthy and seriously effective, and the first one is:
Lift weights - and make sure they're heavy weights. Building muscle is the only long-term method of increasing metabolism. If you fret about 'bulking up' you can elect to stay where you are, fitness and size-wise. It really is the choice available.
The rest include:
get enough rest -- under-sleeping is as bad for shaping up and having energy as working out too much;
drink enough water -- dehydration interfers with every body process, from burning fat to building muscle, and it may not only be what is making you tired but also what is making you think you're hungry;
try including 'thermic' foods -- the ones that seem to increase metabolism for a short time: tumeric (yellow spice used in Asian cooking), cinnamon, green tea, and hot peppers;
work out harder, not longer -- adding time to your easy workout will not give you the energy promised, so add sprints, hills, arm movements, increase the tension on the spin bike or rowing maching, but do not add wrist or ankle weights
have a complete rest day or two a week -- if you do not give your body adequate time to recover from strenuous workouts, you get more and more tired, damage your immune system and lose muscle and endurance
and
make sure you are actually eating *enough* -- inadequate food will also slow you down, in order to conserve the necessary fat stores to make it through the apparent famine, slow your metabolism down (same reason) and make you burn muscle, not fat, for energy (including, in extreme cases, your heart muscle). Lots of smallish meals, each with protein, healthy fat and large quantities of fresh vegetables and fruits (with or without whole grains or animal products) will keep your body convinced there is 'plenty' so it can release stored fat, build muscle and keep you fueled so your energy level is high. The key, though, is lots and lots of vegetables and fruits -- low-calorie, long-chewing, satisfying-for-longer than more processed choices, particularly when eaten with protein and some healthy fat (olives and their oil, fatty fish, avocado, nuts and seeds and their oils)