Scientists Provide an Explanation for the Placebo Effect

Scientists may finally have an explanation for the effectiveness of placebos. It’s been known for a while that people taking a placebo sometimes feel better even though they’re taking a pill without any active ingredients. This phenomenon, called the placebo effect, happens when the patient fully believes that they’re being treated. In a paper just published in the journal Nature Medicine, researchers found that the placebo effect can activate the brain’s reward system. This activation leads to a boosted immune system, providing a possible reason for the effectiveness of placebos.

Past research had already shown that the placebo effect stimulated the brain’s reward system, responsible for pleasure sensations. In this study, scientists artificially activated the ventral tegmental area of the brain in mice. This area is responsible for many key events in the brain’s reward system, including the release of dopamine. Dopamine is known as the “feel good” chemical and is involved in nearly every reward and pleasure center.

The mice were then exposed to the bacteria Escherichia coli. The group that had received the brain treatment showed much better immunological responses. Their T cells, important players in the body’s immune response, were active and had a heightened sensitivity. The experimental group’s monocytes and macrophages, also important in the body’s immune system, showed greater efficiency and eliminated more of the bacteria. These findings show that activation of the ventral tegmental area, such as during the placebo effect, can boost the immune system.

The authors believe that this effect is at least partially due to evolution. If the immune system is enhanced when the reward system is activated, it would give that animal an advantage. The researchers hope that their findings could be used to identify molecules that reproduce these effects. There’s also potential for developing drugs that take advantage of these mechanisms, providing an easy way to give the immune system a quick boost.


Tamar L Ben-Shaanan et al. Activation of the reward system boosts innate and adaptive immunity. Nature Medicine (2016).

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