IT'S ALL IN YOUR HEAD:

When it comes to depression, however, placebos have been acting a bit strange over the past few decades: They've been getting more potent since at least the 1980s. A number of studies have shown this is the case for pill-based placebos, and a few have hinted that it applies to transcranial magnetic stimulation as well. The new study aims to be a comprehensive meta-analysis that's large enough to both test whether the improvement really exists, and to figure out if it's associated with any specific types of study.

The researchers started with a pool of over 2,700 individual studies that used transcranial magnetic stimulation to treat depression. After selecting for high-quality clinical trial data that included randomization and blinding, they were left with only 52 trials and a total of 4,500 participants, about half of which received a placebo treatment.

These placebos always involved hardware, but the hardware could be either inoperative or mis-directed. The non-placebo treatments included a variety of different transcranial magnetic stimulation approaches.

Since you can't really do a placebo control for a placebo, the work simply focused on whether the participants reported improvements in their conditions. And, in fact, the placebos did, pretty consistently, although the actual treatment typically had a larger effect. (Using a measure called the "response magnitude," the placebo was rated at 24 percent, while the actual treatment hit 38 percent.)

To look into whether things were changing over time, the researchers divided the trials up into two batches, one covering the years between 1999 and 2007, and a second covering 2018 to 2022. The effect of both the placebo and the treatment went up over time. The two, however, went up in parallel, so the change didn't affect the trial outcomes.

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