Actually, yes they do. They've been known to work on asthma patients, cancer patients, migraine sufferers, and even drug addicts
"This is an example of the placebo effect - a self-made natural healing response of the body. A patient's belief in the treatment and the placebo response are dependent upon a variety of factors. First, the patient's expectations of treatment effects clearly influence the responses. For example, a study in England was done where 100 men were told that they were taking chemotherapy, when in actuality they were taking inactive saline solution. 20% of these men lost their hair, demonstrating the power of the belief of effects of the treatment. (4) Second, the relationship between patient and care-provider is quite important in determining treatment (or placebo) results. If there is a positive rapport between the two, then most often there will be a positive enthusiasm for the treatment, and therefore a positive outcome, no matter if a placebo or pharmacologic treatment was used. The friendliness, interest, sympathy, prestige, and positive attitude of the care- provider toward the patient and toward the treatment are associated with positive effects of placebos as well as of active treatments. For example, in a double- blind study of dental extractions, two groups were compared: the first, where the doctors knew they would administer either a narcotic analgesic, a placebo, or a narcotic antagonistic and the second, where the doctors knew they would administer either a placebo or narcotic antagonist. The patients from the first group who received placebo had significantly less pain. Since the two placebo groups were only different in the doctors' knowledge of possible treatment, this knowledge must have resulted in differences in behaviors by the doctor that influenced patient responses (3). Third, placebos have time- effect curves and peaks, cumulative and carryover effects after end of treatment which are quite similar to those of pharmacologically active medications. For example, "when varying doses of analgesic followed by a placebo are administered, patients' placebo responses correspond in degree of pain relief over time to their original dosage of analgesic" (3). In addition, dose-response effects have also been documented where two placebo pills were demonstrated to have more pronounced effects than one. "
Make sure you understand what I'm speaking of before you bash what I'm speaking of.