As many consumer and medical associations denounce, lots of miracle-products promise solving a huge variety of health problems without any side effect. Not surprisingly, health authorities have sometimes intervened to stop the distribution of allegedly healing products that actually produce no more therapeutic effect than placebo. These placebos enjoy enormous popularity and are so attractive to the public that they can even become dangerous, specially when they replace the medicines that have been proven effective in clinical tests. If these miracle-products, available in pharmacies and herbal remedies' stores, have no effectiveness at all to heal any disease, why are they so popular today? Perhaps one of the reasons has to do with the fact that they are frequently advertised as "free from side effects", a statement that is usually right. On the other hand, everybody knows that conventional medicines such as antibiotics and analgesics can produce discomforts (e.g. gastric distress), despite their reasonable performance in treating a disease. In a recent publication, researchers from the University of Deusto (Spain) propose that a general cognitive bias underlies this preference for alternative medicines despite their complete lack of therapeutic value. To test their hypothesis, the researchers carried out an experiment, similar to an online videogame, where anonymous participants were able to decide whether or not they would give a fictional medicine to a series of "virtual" patients suffering from the same disease. Although the participants were not warned about this point, the medicine they were using was completely useless against the disease they were treating (it was even unable to produce any placebo effect). In fact, the computer program was programmed so that a high number of patients showed a spontaneous remission, regardless of whether they were given the medicine. First, the researchers found that the useless medicine was used much more frequently during the experiment when it was described as "free from side effects", just as it seems to happen in real life. More interestingly, the more often the participants gave the completely useless medicine to the patients, the more pronouncedly they overestimated its effectiveness. As a result, at the end of the experiment, many participants developed the belief that a product with no ability to heal a disease was in fact highly effective. Based on these findings, the researchers propose that, if health authorities worldwide aim to prevent the spread of completely useless miracle-products, they should put the stress on the benefit of using therapies that have been proven effective in clinical tests, and stop emphasizing the benefit of the lack of side effects, because highlighting the latter might lead people to erroneously perceive a useless placebo as highly effective.