西亚试剂：Only in America

This effect would explain why drug companies have trouble getting new painkillers through trials, notes neuroscientist Fabrizio Benedetti, who studies placebo responses at the University of Turin, Italy. Over the past ten years, he says, more than 90% of potential drugs for treatment of neuropathic and cancer pain have failed at advanced phases of clinical trials.

But the finding that placebo responses are rising only in the United States is the most surprising aspect of the latest analysis. One possible explanation is that direct-to-consumer advertising for drugs — allowed only in the United States and New Zealand — has increased people’s expectations of the benefits of drugs, creating stronger placebo effects. But Mogil’s results hint at another factor. "Our data suggest that the longer a trial is and the bigger a trial is, the bigger the placebo is going to be," he says.

Longer, bigger US trials probably cost more, and the glamour and gloss of their presentation might indirectly enhance patients’ expectations, Mogil speculates. Some larger US trials also use contract research organizations that can employ nurses who are dedicated to the trial patients, he adds — giving patients a very different experience compared to those who take part in a small trial run by an academic lab, for instance, where research nurses may have many other responsibilities.

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