The first time the placebo effect really got under my skin was when I read that roughly one-third of people with irritable bowel syndrome improve on placebo treatments alone. Usually this statistic is presented as a fascinating quirk of medicine. My reaction was anger.
Humanity possesses an extremely effective treatment, with essentially zero side effects - and patients need someone else's permission to use it.
The placebo effect refers to the improvements in symptoms that patients experience after they're given an inert treatment like a sugar pill. Driven by expectation, context and social cues rather than pharmacology, the placebo effect is often dismissed as all in the mind . But decades of research have shown it is anything but imaginary.
Placebo treatments can trigger measurable changes in the brain , immune system and hormone function. In studies on pain, placebos cause the brain to release endorphins, the body's natural opioids . In Parkinson's disease, placebo injections increase dopamine activity in the brain. The placebo effect isn't magic. It's biology.
Having spent nearly a quarter-century teaching evolutionary medicine , I've come to see placebos not as curiosities of clinical trials but as windows into how human biology responds to social signals. And it's that relationship that is exactly what makes the placebo effect unsettling.
Medicine works, even when it isn't medicine
The placebo effect is so reliable that researchers must account for it in nearly every clinical trial .
When testing a new drug, scientists compare its effects to what patients experience on a placebo treatment like sugar pills, saline injections or sham surgery. If the drug doesn't outperform the placebo, it rarely reaches the public. Placebo responses are common and powerful enough to rival active treatments.
Even surgery isn't immune to the placebo effect. In several well-documented studies of knee procedures , patients who received sham operations - incisions without the full surgical repair - improved almost as much as those who received the real procedure.
Clearly something real is happening inside the body. But the strangest part of the placebo effect is not that it works. It's what makes it work.
The prescription of belief
Placebo treatments tend to be more effective when delivered by credible authorities . Pills work better when prescribed by doctors wearing white coats. Expensive pills outperform cheap ones. Injections produce stronger responses than tablets.
Some researchers have even removed the deception from placebo experiments entirely. In open-label placebo studies , patients are directly told they are receiving a placebo; and yet many still report significant improvement.
But look more closely at how these studies are run. Patients are not simply handed a sugar pill and sent home. They receive an explanation from a clinician, in a medical setting, within a structured ritual of care : a context that may be doing much of the biological work.
Even when the deception disappears, the social scaffolding remains. The permission to heal is still being granted by someone else.
The placebo effect extends beyond the patient
The placebo effect is often framed as something happening inside an individual. But it does not operate in isolation.
Consider what happens in veterinary medicine. Dogs and cats cannot believe a treatment they're given will work; they have no concept of receiving medication. Yet when owners and vets believe an animal is being treated, they consistently report improvements in pain and mobility that medical tests do not confirm.
In one study of dogs with osteoarthritis , owners reported improvement roughly 57% of the time for animals receiving only a placebo.
The animals themselves may not have improved. But the humans caring for them perceived they had. The healing signal, it turns out, travels through the humans in the room.
When healing makes things worse
There have been times when going to the doctor made you less likely to survive. In the 19th century, mainstream medicine was built on bloodletting, purging and doses of mercury and arsenic - treatments that killed as often as they cured.
Homeopathy emerged in the late 18th century precisely in this context. Its founder, Samuel Hahnemann , was a physician horrified by the harm the conventional medicine of his time was causing. His highly diluted versions of contemporary remedies did nothing pharmacologically. But they also did not kill people, which put them decisively ahead of the competition.
Homeopathic patients not only survived but also reported dramatic recoveries from chronic ailments and acute infections alike. During the cholera epidemics of the mid-1800s, patients at homeopathic hospitals had lower death rates than those receiving standard care. Why was that?
The standard cholera treatment of the era was aggressive and exhausting; for a disease that already caused massive fluid loss, doctors often prescribed further bloodletting, along with toxic purgatives such as calomel - a form of mercury - to "flush" the system. In contrast, homeopathic care involved extreme dilutions of substances in water or alcohol, effectively providing hydration and a calm, structured environment without the physiological assault.
Death rates were lower not because homeopathy worked but because the placebo effect - combined with not poisoning patients - was more effective than the medicine of the day.
Healing is not free
The body needs resources to heal from injury and disease. Activating systems such as immune responses, tissue repair and inflammation at the wrong time can be dangerous.
A full-scale immune response is metabolically expensive , with fever increasing metabolic rate by roughly 10% per degree Celsius rise in body temperature . Triggered at the wrong time, this can deplete critical energy reserves needed for immediate survival , such as escaping a predator. Furthermore, misplaced or overzealous inflammation causes collateral damage to healthy tissues, potentially leading to chronic dysfunction.
Some researchers have proposed that placebo responses reflect a kind of biological health governor : a system that regulates when the body invests heavily in recovery. Cues from trusted individuals may be exactly the signal the body waits for before committing resources to recovery. A caregiver's reassurance, a physician's authority and the rituals of medicine may tell the body that conditions are finally stable enough to devote energy to healing.
If that interpretation is correct, the placebo effect is not a trick of the mind. It is an ancient biological system responding to social information.
Body under stress
The placebo effect resembles another system people struggle with today: the stress response .
Stress evolved to keep you alive in the face of acute danger - predators, famine, immediate physical threat. These days, this useful piece of biological engineering might fire when someone hasn't replied to your email. The system that once saved people's lives now makes many miserable over things that would have been unimaginable to their ancestors.
You can talk back to the stress response, consciously reappraising the threat - in other words, reframing a looming deadline not as a catastrophe but as a manageable challenge - to help quiet it. But notice what you cannot do: You cannot simply decide to activate your placebo response. You cannot will yourself to release pain-relieving endorphins by believing hard enough in a sugar pill. For that, you still need the ritual, the white coat, the authority figure. You need someone else.
The stress response, misfiring as it is, remains yours. The placebo response has been outsourced: not because it wasn't always social, but because even now, people still can't seem to access it on their own.
The uncomfortable implication
The placebo effect is not a trick of the mind. It is a feature of human biology that people have largely surrendered to whoever performs authority most convincingly.
If belief can activate biological healing pathways, belief can also be manipulated . Charismatic figures, elaborate medical rituals and expensive treatments may produce real improvement in symptoms even when the underlying treatment is physiologically inert. That is how wellness culture works. It leverages the same social scaffolding of care to trigger the body's internal pharmacy, regardless of whether the treatment itself does anything.
The placebo effect is often celebrated as proof that the mind can heal the body. But I believe that may not be its most interesting lesson. It also reveals that human physiology evolved to take its cues from other people. Your brain, immune system and pain response are not isolated machines. They are deeply intertwined with social signals, expectations and trust .
In a world filled with doctors, advertisements, wellness influencers and elaborate medical rituals, that insight is both fascinating and profoundly maddening. People are walking around with one of the most powerful healing systems ever documented locked inside them, and they can reliably access it only when someone in a position of authority gives them permission.
Phil Starks does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
