Why is the placebo effect getting worse, but only in America?

But there’s an even simpler explanation: clinical trials last much longer than they used to. Since 1990, the average clinical trial in the U.S. has gone from lasting four weeks to lasting twelve weeks. Why is this such a big deal? Because symptoms (especially pain) tend to naturally improve over time. If you’re feeling bad one day, it is likely that you will feel better a few weeks later. Thus, the longer a trial, the larger the placebo effect is likely to be.

This exposes a common myth: that placebos actually trigger some sort of innate healing ability. They do not. Placebos simply alter our perception of symptoms. This was beautifully demonstrated in a study comparing albuterol, a drug that opens airways, to two different placebo treatments for asthma. When asked, patients reported that the two placebo treatments improved their asthma symptoms just as well as albuterol. But when scientists actually examined patients’ lung function, only albuterol meaningfully improved airflow. Prior studies have also demonstrated that placebo interventions do not treat patients’ cancers, only their associated symptoms.