These are usually vitamins or mild painkillers, but sometimes stronger drugs inappropriate for the specific ailment. There is scientific evidence some patients improve with placebos, simply because they think it's something that will make them better.
But the AMA insists it doesn't matter, arguing placebo treatment is unethical because doctors should always be up front with their patients. If the idea that your doctor might not tell you the truth makes you a bit queasy, ask him or her about it at your next appointment. But just check the label before taking anything for that queasiness, just to make sure it's the real thing.