People are notoriously susceptible to the placebo effect, in which a fake treatment can improve our condition simply because we, believing it's real, expect it to work. Clinical trials for new drugs compensate for this tendency by administering sugar pills or other inactive treatments to some patients to tease out whether a medication is actually effective or if people are merely fooling themselves into believing their condition has improved.

While it’s important for scientists to find treatments that actually do help people, the placebo effect may not be all bad. A new study of pain medication placebos finds that even when people know they’re not taking a real medication, they can be conditioned to feel pain relief from the fake treatment. 

The study, published in the Journal of Pain, included 54 participants who were told they were going to receive either a “pain-relieving” cream or a cream with no active ingredients. (Both "creams" were actually just petroleum jelly.) Researchers from the University of Colorado at Boulder's Cognitive and Affective Neuroscience Lab administered both creams to participants, describing the blue cream as pain relieving (the placebo) and the neutral jelly as inactive (the control).They then advised the participants on potential side effects.

After each cream had been put on their arm, the participants received a hot stimulus designed to measure their perception of pain. In the placebo condition, the researchers turned down the heat after the fake pain-relief cream was administered, leading the patients to believe the blue cream was working.

Over the next few weeks, some participants received four of these "treatments," or conditioning sessions. The rest of the subjects received just one. Then the researchers revealed to the participants that both the "pain relief" blue cream and the clear petroleum jelly were actually both inactive. 

They then re-tested all participants' responses to the blue cream placebo. And here's the interesting twist: the participants who had four treatments reported feeling pain relief from the blue cream—even though they knew the treatment was fake. Meanwhile, the participants who had experienced only one treatment did not.

This suggests that conditioning someone through repeated "treatments" to expect pain relief from a placebo can lead to real pain relief. 

"We're still learning a lot about the critical ingredients of placebo effects," Tor Wager, senior author of the study, said in a press statement. "What we think now is that they require both belief in the power of the treatment and experiences that are consistent with those beliefs. Those experiences make the brain learn to respond to the treatment as a real event. After the learning has occurred, your brain can still respond to the placebo even if you no longer believe in it."

One potential use for this finding is that people might be able to stop taking drugs but continue feeling similar levels of relief. "If a child has experience with a drug working, you could wean them off the drug, or switch that drug [with] a placebo, and have them continue taking it," as study co-author Scott Schafer explains

However, it might not work equally for all patients. Previous research indicates that there may be a genetic underpinning that makes some people more susceptible to the placebo effect than others.