Answer: The simple answer is that they are prescription medications that are approved by FDA for weight loss.
Answer: Good question and the answer isn't simple. The commonly-prescribed weight loss drugs include phentermine, phendimetrazine, diethylpropion and orlistat. These are all "NON-amphetamine" prescription diet drugs although the first three are controlled substances. There are however a number of amphetamines that are still technically "approved" for weight loss and these include phenmetrazine (Preludin) and dexedrine. I do not prescribe phenmetrazine or dexedrine for weight loss.
Let's be specific: from this point forward I will speak only of phentermine, phendimetrazine and diethylpropion. I won't include orlistat in this discussion because it is so different and I'll exclude the amphetamines since I never prescribe them.
Answer: Yes. Not only are they effective for weight loss, they are efficacious for weight loss.
Answer: By themselves, absent lifestyle changes, their efficacy is so-so, but they are the best we've got.
Answer: People taking phentermine for example, lose, over three months, about 6-10% of their body weight--and that's WITH diet and exercise. People taking placebo lose more like 3-6%.
Answer: Not even close.
Answer: Because obesity is such a terrible illness and even small reductions in body weight cause significant improvements in health.
Answer: No drug is totally safe but prescription diet drugs are some of the safest. They have been on the US market over 50 years and millions of people have taken them. Again, the risk of any drug has to be weighed against the likely benefit and even though prescription diet drugs don't produce massive weight loss in most cases, they DO work and obesity is REALLY dangerous.
Question: How long can people take them?
Answer: That is a matter of debate. The actual prescribing guidelines for these agents say three months and no longer. Most experts believe this is absurd. I tend to agree. Obesity is a chronic illness and we treat all other chronic illness chronically.
Answer: Yes. Of them, Qnexa by Vivus seems the most promising and very likely will reach the US market in 2012. It's not a game-changer though. Qnexa is a combination pill composed of phentermine and topiramate, an anti-seizure drug that has weight-loss properties. It seems to work a little better than phentermine alone.
Answer: No. But let's be clear about what addiction means. Generally, to be addicting a drug must produce dependence, tolerance, progression and what we call "continued use despite adverse consequences." In other words, drug addicts need their drug to feel good, the longer they use it the less well it works, they need (and take) more and more over time, and no matter how badly the drug ruins their lives, they keep using. THAT is addiction. Prescription diet pills don't cause that.
Answer: BUT, prescription diet pills DO produce tolerance (they don't work as well later as early) and they do cause appetite-suppression that is drug-dependent. In other words, when people stop taking prescription appetite medications, they do feel hungrier than when taking them. That is why people MUST change their diet and must exercise. Appetite medications don't cure anyone.