New research is zeroing in on a biochemical basis for the placebo effect — possibly opening a Pandora’s box for Western medicine.

One is that a placebo doesn’t change a person’s underlying biology related to the condition. Instead, it affects how the person experiences or reacts to an illness. In some settings, placebos can trigger the brain’s reward system,” Jeremy Howick of the University of Oxford, who is working on ways to maximize the placebo effect, told Quartz. “It releases chemicals that changes how people feel.” Another theory, from Nicholas Humphreys, a retired psychologist formerly at the London School of Economics, is that placebos are just a way of triggering the immune system. From a biological perspective, immune systems are a huge expense and may drain an animal’s energy reserve. So perhaps placebos act as a signal to get the immune system going. But none of those theories explain why the placebo effect is getting stronger. One explanation is advertising. The US and New Zealand are the only two countries where direct-to-consumer advertising of drugs is legal. The fact that more people are believing that pills work, means the stronger the placebo effect.