Placebo, Nocebo Effects Can Influence Pain Perception at Unconscious Level

Karen Lee Richards Health Guide
  • Most of us are familiar with the placebo effect––the benefit patients sometimes receive from a treatment that has no active components. But did you know there is also a nocebo effect? The nocebo effect occurs when patients experience negative side effects from a treatment that has no active components.


    It has long been believed that placebo responses are related to conscious beliefs or thoughts––that when given an inert pill or therapy, patients get better because they have the expectation that they will get better. Or in the case of nocebos, patients experience side effects because they anticipate that they will have side effects.

    Add This Infographic to Your Website or Blog With This Code:


    However, new research, published in the September 10 on-line issue of the Proceedings of the National Academy of Sciences (PNAS), calls this long-held belief into question.


    "In this study, we used a novel experimental design and found that placebo and nocebo effects rely on brain mechanisms that are not dependent on cognitive awareness," explains first author Karin Jensen, PhD, of the Department of Psychiatry and the Martinos Center for Biomedical Imaging at Massachusetts General Hospital (MGH) and the Program in Placebo Studies (PiPS) at Beth Israel Deaconess Medical Center/Harvard Medical School. "A person can have a placebo or nocebo response even if he or she is unaware of any suggestion of improvement or anticipation of getting worse."


    Study Design and Results


    For this study, the researchers conducted two experiments using 40 healthy volunteers (24 female; 16 male, median age 23).

    1. In the first experiment, researchers administered heat stimulation to participants' arms while simultaneously showing them images of male human faces on a computer screen. The first face was associated with low pain stimulations and the second image with high pain. The subjects were then shown the faces again, along with a heat stimulus, and asked to rate their pain on a 0-to-100 scale; however, unknown to the subjects, all heat stimulations had the same moderate intensity. As predicted, the pain ratings correlated with the previously learned associations, with a pain rating of 19 when the subjects saw the low pain face while the high pain face resulted in subjects' mean reports of 53 on the pain scale (nocebo effect).

    2. In the second experiment, a different group of participants were administered the same high and low levels of thermal heat stimulation associated with different faces. After that, the facial images were again projected on the computer screen––but this time, they flashed by so quickly that subjects could not consciously recognize them. Despite a lack of consciously recognizable cues, when the participants rated their pain, they reported a mean pain rating of 25 in response to the low pain face (placebo effect) and a mean pain rating of 44 in response to the high pain face (nocebo effect).

    PiPS Director and study coauthor Ted Kaptchuk notes, "It's not what patients think will happen [that influences outcomes] it's what the nonconscious mind anticipates despite any conscious thoughts. This mechanism is automatic, fast and powerful, and does not depend on deliberation and judgment. These findings open an entirely new door towards understanding placebos and the ritual of medicine."


    Add This Infographic to Your Website or Blog With This Code:

    My Thoughts...


    We've known for a long time that the power of suggestion can play a big part in how we respond to pain and various therapies or treatments on a conscious level, but seeing evidence that our unconscious mind may also be influencing our responses is fascinating.


    I can't say I'm totally surprised. I've always been intrigued by the power and complexity of our brains. And I've long thought that even with all of our technological advances, we've barely scratched the surface of what our brains are capable of doing. Therapies like mindfulness meditation suggest that we may be capable of controlling our pain, at least to some degree, by learning to harness our brain power.


    I can't help but wonder how much our past experiences and beliefs may be playing an unconscious role in how we perceive our pain and respond to various treatments.




    Jensen KB, et al. “Nonconscious activation of placebo and nocebo pain responses.” Proceedings of the National Academy of Sciences (PNAS). 2012(Sep 25);109(39):15959-15964.

    Study demonstrates that placebo response occurs at nonconscious level.” EurekAlert. September 10, 2012.


Published On: October 31, 2012