Imagine that someone hands you a perfectly ordinary glass of water and tells you there is something in it that might make you feel nauseated. You drink it, and a few minutes later your stomach begins to feel strange. Maybe you notice a little queasiness that you would normally ignore. Your attention settles on it, you start wondering whether the warning was right, and suddenly you are very aware of every sensation coming from your stomach.

Now imagine discovering that there was never anything unusual in the water.

Were your symptoms imaginary? Were you pretending? Did you somehow think yourself sick?

None of those explanations quite capture what may be happening. Expectations can influence what we experience, particularly with symptoms such as pain, and researchers have a wonderfully spooky name for the negative side of this phenomenon: the nocebo effect.

If the placebo effect is the famous story about positive expectations sometimes contributing to improvement, the nocebo effect is its darker cousin. Negative expectations can sometimes contribute to increased symptoms or unpleasant experiences. Researchers have demonstrated nocebo effects experimentally, and they have begun identifying some of the psychological and biological processes involved.

Which brings us to the perfect question for spooky season: if someone convinced you that you were cursed, could the belief actually hurt you?

The answer is more interesting than either a simple yes or no.

Meet Placebo’s Evil Twin

Most of us have heard of the placebo effect, although it is often misunderstood. A placebo isn’t simply something that happens because a person is gullible, nor does a placebo response mean that someone’s symptoms weren’t real. Modern placebo research examines how the context surrounding a treatment—including expectations, previous experiences, learning, and the interaction between a patient and clinician—can influence an outcome.

A nocebo response moves in the opposite direction. Instead of expecting improvement, someone anticipates that something unpleasant is going to happen. Research has found that negative suggestions and expectations can contribute to increased pain and other symptoms under some circumstances. A 2020 review by Luana Colloca and Arthur Barsky in The New England Journal of Medicine describes placebo and nocebo effects as arising through combinations of expectations, prior experiences, information about treatments, and the larger therapeutic context.

Pain provides some of the clearest evidence. In experimental studies, researchers can apply the same physical stimulus while changing what participants have been led to expect about it. Those expectations can alter how painful the stimulus is experienced. A meta-analysis of experimental nocebo studies involving pain found effects that were meaningful but also highly variable, an important reminder that there isn’t one universal nocebo response that affects everyone in the same way.

That variability matters because “expectations affect experience” is a very different claim from “whatever you believe becomes physically true.”

Your Brain Doesn’t Experience Pain in a Vacuum

Pain seems as though it should be straightforward. Something hurts, nerves send a signal, and the brain reports what happened. The actual experience is more complicated.

Signals from the body matter enormously, of course, but pain is an experience produced within a nervous system that is also processing context, attention, emotion, memory, and expectation. If you’ve ever had a bruise that suddenly seemed much more painful after you noticed it, or felt surprisingly little pain from an injury until an emergency was over, you’ve encountered how flexible the experience of pain can be.

Researchers have found that expectations can influence pain-related processing in the central nervous system. Neuroimaging research has identified changes in activity within regions involved in pain processing when people anticipate more or less pain. Other research has investigated neurochemical systems involved in nocebo-related increases in pain.

This is where we need to resist the temptation to turn legitimate neuroscience into neuro-woo. A brain scan showing that expectations influence pain processing does not mean thoughts magically create physical reality. It means that perception isn’t a passive recording of information coming from the body. The brain participates in constructing our experience from incoming signals plus context and prior learning.

That is already strange enough without adding magic.

The Curse Has to Get In Somehow

Suppose someone told you that an object in your home was cursed and that being near it would cause headaches. At first, you might laugh. Later that evening, however, you happen to get a headache.

Now the curse has evidence.

The next day, you walk past the object and notice yourself wondering whether the headache will return. You begin paying closer attention to your forehead, temples, neck, and eyes. A small sensation you ordinarily wouldn’t notice suddenly becomes meaningful because you now have a reason to look for it.

This doesn’t prove that you would develop a nocebo response, and it certainly doesn’t prove that every symptom following a frightening suggestion is caused by expectation. But it illustrates several processes that researchers study: expectation, attention, learning, and previous experience.

Nocebo effects can also be learned through conditioning. If a particular cue has repeatedly been associated with an unpleasant experience, that cue may later influence how a person responds even when the original conditions have changed. Some experimental studies have even produced nocebo-related increases in pain through conditioning without participants consciously expecting greater pain.

That finding makes the story considerably more interesting than simply saying, “You thought something bad would happen, so it did.” Our experiences can teach us associations that influence later responses, sometimes without a neat conscious belief sitting at the center of the process.

When a Warning Becomes Part of the Experience

Nocebo research raises an especially tricky problem in medicine. Patients need accurate information about the possible side effects and risks of treatment. At the same time, the way information is communicated can influence expectations.

Researchers have found that explicit suggestions about symptoms, expectations of experiencing those symptoms, previous experiences, and even observing other people experience symptoms can contribute to nocebo responses. A systematic review examining factors associated with nocebo effects found particularly strong evidence for symptom expectations and explicit suggestions that an exposure would cause symptoms.

That doesn’t mean doctors should hide side effects from patients. Informed consent matters, and people deserve accurate information about their treatment. Instead, this research has encouraged discussion about how risks are communicated. Accurate information doesn’t have to be delivered in a way that unnecessarily heightens fear or implies that a possible side effect is inevitable.

There is also an important distinction between a genuine medication side effect and a nocebo response. If someone develops a symptom after starting a medication, we cannot simply declare that expectation caused it. The drug may be responsible, the symptom may be unrelated, expectations may have contributed, or several factors may be operating together. Nocebo should never become a convenient way of telling someone that a symptom is “all in their head.”

So What Happens If You Believe You’re Cursed?

This is where our spooky-season thought experiment gets interesting.

There is no scientific evidence demonstrating that a supernatural curse can cause illness through some mysterious external force. But if someone genuinely believes that they have been cursed, the fear and expectation surrounding that belief could potentially affect their experience. They might become more attentive to ordinary bodily sensations, interpret ambiguous sensations as signs that something is wrong, experience anxiety or disrupted sleep, or change their behavior because of what they expect to happen.

If a headache appears after the curse, it may feel like confirmation. If nothing happens on Tuesday, that uneventful day probably won’t become part of the story. If another headache appears Thursday, however, the connection becomes even more compelling. Now expectation, attention, pattern recognition, and confirmation bias may all begin reinforcing one another.

This doesn’t mean the headache isn’t real. It means the explanation for a real experience may not be the one that first comes to mind.

That distinction is important because dismissing someone’s symptoms as imaginary misses what nocebo research actually teaches us. Our experiences are produced by brains and bodies constantly interacting with one another and with the world around us. Psychological influences aren’t somehow less real simply because we call them psychological.

But Don’t Blame Yourself for Being Sick

There is an uncomfortable side to conversations about placebo and nocebo effects, particularly when they escape the laboratory and enter wellness culture. It doesn’t take long before “expectations can influence some symptoms” becomes “your thoughts create your health.”

That leap isn’t supported by the evidence.

You cannot simply positive-think your way out of every illness, and developing symptoms does not mean that you had the wrong mindset. Disease involves genetics, pathogens, injury, immune processes, environmental exposures, social conditions, physiology, chance, and countless other factors. Expectations are one possible influence on some experiences and outcomes, not a master control panel for the human body.

This is particularly important when we talk about pain. Saying that expectations can influence pain does not mean pain is imaginary. Pain is an experience generated by the nervous system, and many different biological and psychological factors can influence it. Understanding that complexity should make us take people’s experiences more seriously, not less.

Nocebo research gives us another piece of that complicated puzzle. It doesn’t give us permission to blame people for their symptoms.

The Spell Is the Story

There is something wonderfully appropriate about calling this phenomenon the nocebo effect because it brings us back to one of the oldest ideas in magic: words have power.

Not supernatural power, as far as the evidence shows, but words can shape expectations. Expectations can influence attention. Experiences can create associations. Context can change how we interpret what we feel. In some circumstances, those processes can even influence the intensity of symptoms such as pain.

A curse works as a perfect metaphor because a curse gives you a story about what is going to happen next. Once you have that story, every strange sensation has somewhere to belong.

Science doesn’t tell us that curses are real. It tells us something I find much more fascinating: what we expect can sometimes become part of what we experience.

That doesn’t mean our minds control reality. It means our brains aren’t standing outside reality simply observing it. They are constantly interpreting what is happening, using what has happened before and what we expect might happen next.

Maybe that isn’t witchcraft, but for something happening inside a few pounds of tissue behind your eyes, it is still pretty remarkable.

Next Time: Things That Go Bump in the Brain

Next week, we’re going somewhere even more appropriate for October: a haunted house.

Why can an empty room suddenly feel as though someone else is standing in it? Why do shadows become figures, ordinary noises become footsteps, and unfamiliar places sometimes produce the unmistakable feeling that we aren’t alone?

We’ll explore expectation, ambiguous sensory information, hypervigilance, and the strange phenomenon researchers call sensed presence as we ask what science can—and cannot—tell us about why some places feel haunted.

References & Further Reading

Benedetti, F., Amanzio, M., Casadio, C., Oliaro, A., & Maggi, G. (1997). Blockade of nocebo hyperalgesia by the cholecystokinin antagonist proglumide. Pain, 71(2), 135–140. https://doi.org/10.1016/S0304-3959(97)03346-0

Benedetti, F., Amanzio, M., Vighetti, S., & Asteggiano, G. (2006). The biochemical and neuroendocrine bases of the hyperalgesic nocebo effect. The Journal of Neuroscience, 26(46), 12014–12022. https://doi.org/10.1523/JNEUROSCI.2947-06.2006

Colloca, L., & Barsky, A. J. (2020). Placebo and nocebo effects. The New England Journal of Medicine, 382(6), 554–561. https://doi.org/10.1056/NEJMra1907805

Petersen, G. L., Finnerup, N. B., Colloca, L., Amanzio, M., Price, D. D., Jensen, T. S., & Vase, L. (2014). The magnitude of nocebo effects in pain: A meta-analysis. Pain, 155(8), 1426–1434. https://doi.org/10.1016/j.pain.2014.04.016

Webster, R. K., Weinman, J., & Rubin, G. J. (2016). A systematic review of factors that contribute to nocebo effects. Health Psychology, 35(12), 1334–1355. https://doi.org/10.1037/hea0000416