Whenever medical researchers conduct clinical trials of a new drug, they have to account for the placebo effect—the fact that if you give people a treatment, even if it’s sugar pills, some of them will feel better. Though the treatment might be inactive, patients (and sometimes even the investigators in charge of the study) have an implicit bias toward believing that it works. Whether or not you’re the kind of person who feels better after taking a placebo may have something to do with your genes, though, as a new study from Trends in Molecular Medicine argues.

Recent research has shown that the placebo effect isn’t just psychological—it’s physiological. Several things happen when you take a placebo, including anxiety reduction, pain suppression, or the activation of reward centers in the brain, which might make you feel better. When you think about it, a placebo can be a beautiful thing. Why wouldn’t you want to feel better without having to pay for real medicine (which might also come with annoying side effects)?

Hence, it would be nice to be able to figure out who, exactly, is most susceptible to the placebo effect, since not everyone feels great after a course of sugar pills. Led by Kathryn Hall of Harvard Medical School, a group of scientists reviewed previous research for evidence of a genetic variation in the placebo effect by looking for correlations between certain genetic mutations and the strength of a person’s placebo response. Common genetic mutations called Single nucleotide polymorphisms, or SNPs, have been implicated in changing the placebo response in clinical trials. Hall and her team found 11 of these SNPs to be associated with the placebo response in previous research, including those in the dopamine system (the brain’s reward system), the serotonin system (which deals with mood), and the opioid and cannabinoid systems (which both deal with pain).

With this evidence, it’s looking like the placebo response is even more complicated than we thought. “Given the complex interplay of behavior, expectation, neurotransmitter signaling, disease, and the context of the medical treatment ritual, the molecular pathways and genes involved in contributing to placebo responses is unfolding as a potentially complex network,” the researchers write.

This study is just a preliminary look into the genetics of placebo responses, but if your response to placebos is coded into your genes, that could affect the reliability of studies that measure a drug’s efficacy against the efficacy of the placebo treatment. If a trial featured all people who respond strongly to placebos in the control group, for instance, the results would skew toward indicating that the drug treatment was completely ineffective. Furthermore, it could lead to honest placebo treatments, where patients knowingly receive placebo treatments (as has been suggested for certain conditions, like Irritable Bowel Syndrome). Because in some cases, feeling better is more important than which medicine you take.

[h/t: The Economist]