The Strange Biology Of Meaning
Dylan Evans’ book Placebo: Mind Over Matter in Modern Medicine remains one of the sharpest investigations into how belief shapes biology, and why that should unsettle both sceptics and true believers alike. First published in the early 2000s, the book arrived before “mind-body medicine” had become a wellness aisle, and Evans’ line of questioning remains the vital force: what can belief really do, and where does the fantasy begin?
His answer is neither cynical nor credulous; Placebo is not proof that thought can cure anything and neither is it a medical parlour trick. It is better understood as the body responding to a situation: the pill, the doctor, the diagnosis, the ritual, the room, the language, and the expectation of care. The “mind” in placebo is part of a living organism embedded in a world.
Dylan Evans is a British writer, philosopher and former academic who received his PhD in philosophy from the London School of Economics, before teaching philosophy at King’s College London, and then working in robotics at the University of Bath. His credibility derives from his hybrid background: philosophy, cognitive science, emotion research, health-adjacent behavioural science, and a slightly eccentric willingness to test ideas against life rather than leave them safely pickled in theory.
The Myth Machine
Sometime in the 1950s, an American anaesthesiologist named Henry Beecher transformed medical history – or so the story goes. Returning from the battlefields of World War II, where he had observed soldiers receiving injections of saline when morphine ran out and still reporting relief, Beecher published a landmark paper arguing that roughly 35% of patients benefit meaningfully from placebos.
The sugar pill, it seemed, had power. Placebo, from the Latin “I shall please”, entered the clinical canon not merely as a control condition to be outwitted, but as evidence of the healing mind’s formidable reach. This, Evans argues, was both a scientific distortion and a cultural convenience.
For half a century, this idea quietly colonised medicine, lending scientific respectability to the claims of faith healers, alternative therapists, and anyone who had ever insisted that attitude is everything. Then, in 2001, Danish researchers Asbjørn Hróbjartsson and Peter Gøtzsche published a systematic review of 114 randomised trials comparing placebo treatment with no treatment at all.
After reviewing the data, they found that compared to no treatment, placebo had no significant effect on binary outcomes, regardless of whether these outcomes were subjective or objective. Beecher had conflated natural recovery, regression to the mean, and actual placebo response: three very different phenomena that happen to look identical without a no-treatment control group.
What Hróbjartsson and Gøtzsche revealed is that much of what we called the “placebo effect” was actually just time passing. Sick people get better, they return to clinics when their symptoms are worst (regression to the mean), and may then improve whether treated or not. Strip away these confounds, and the inert pill’s magic considerably dims, especially for objective disease outcomes, although subjective symptoms such as pain remain a more promising and complicated case.
Evans treats both camps with equal scrutiny: Beecher and others who claimed broad powers for placebo, and later detractors who suggested there may be no placebo effect at all. Among the other questions he examines is the paucity of research comparing placebos to no treatment. His conclusion is more nuanced than either camp: placebos do work – but on a specific, biologically bounded set of conditions, and through mechanisms that are far more concrete than “the power of positive thinking.”
The Body’s Pharmacy
The clearest evidence for placebo efficacy comes from pain research, where the findings are neurobiologically striking. Placebo analgesia appears to be mediated in large part by the brain’s endogenous opioid system, particularly through μ-opioid receptors. These same systems are also involved in stress regulation, pain modulation, hormonal signalling through the hypothalamic-pituitary axis, and responses to novel or emotionally salient stimuli. In other words, when someone believes they have received a painkiller and feels relief, the brain is not simply being fooled into false comfort. It may be recruiting its own pain-relieving chemistry.
While often attributed to the opioid system, recent literature suggests that placebo responses activate additional neurotransmitter pathways, including dopamine pathways in the brain, which are intrinsically linked to the brain’s reward and motivational system. This supports the idea that expectation is not merely cognitive; it recruits circuitry that can shape how relief is anticipated and experienced.
This is where Evans’ evolutionary contribution becomes most provocative. Drawing on immunology, he proposes that placebos work by triggering, and then modulating, what he calls the acute phase response: the body’s immediate, energetically costly immune reaction to perceived threat. This occurs, he suggests, through suppression of the acute phase response as revealed in such signs as pain, inflammation, swelling and fever. Evans believes that the historical evolution of different aspects of the human body offers a way to fill gaps in knowledge of the placebo response – notably, immune reactions of various evolutionary ages.
The theory is elegant. The innate immune system and the brain evolved together, communicating through a shared molecular vocabulary of cytokines, hormones, and neural signals. When a patient receives treatment in a context of care – from a trusted healer, within a meaningful ritual – the brain may interpret this as a signal that help has arrived, and the body can afford to modulate its costly defensive responses. This is not mental magic, it is resource allocation by organisms that evolved under conditions where social support genuinely predicted recovery.
Crucially, Evans uses this framework to define the limits of placebo. An explorative analysis of outcome parameters and strength of placebo effects yielded a classification into responsive “physical” versus non-responsive “biochemical” parameters. In total, 50% of trials measuring physical parameters showed significant placebo effects, compared with 6% of trials measuring biochemical parameters. Contrary to claims from the likes of Joe Dispenza – you cannot think away a tumour, and you cannot believe yourself out of a bacterial infection. The placebo effect is real, but it operates within biological lanes: pain, mood, anxiety, gastrointestinal symptoms, certain inflammatory conditions. Beyond those lanes, belief hits a wall.
Meaning As Medicine
What Evans gestures toward but doesn’t fully develop is the anthropological dimension that his philosopher’s frame partly obscures. Anthropologist Daniel Moerman, writing around the same time, proposed replacing the term “placebo effect” with the meaning response: the physiological or psychological effects of meaning in the origins or treatment of illness.
These are not “non-specific” effects: meanings are concrete, and are often quite specific in principle. The pill’s colour, size, price, and the confidence of the prescriber have all been shown to modulate outcomes. A red pill is more effective as a stimulant; a blue one as a sedative. An injection outperforms a tablet, and surgery may outperform both. Expensive treatments often produce stronger placebo responses than cheap ones.
The implications are unsettling: medicine’s active ingredient is partly theatre. The white coat, the consulting room, the ceremony of examination and prescription – these are, in Moerman’s terms, culturally encoded symbols that speak directly to the body’s healing mechanisms. They do not merely accompany treatment; for a meaningful portion of patients, they are the treatment. This insight naturally extends into the interpersonal.
Patient expectancies drive placebo and nocebo phenomena, which can be shaped through contextual factors including verbal suggestions, conditioning, and social observation. The nocebo effect – the dark twin of the placebo – reminds us that the same mechanisms can harm. When patients are warned of side effects, they report them more. When clinicians communicate doubt or coldness, outcomes worsen. Language, tone, and relationship are not peripheral to healing; they are among its primary instruments.
The nocebo effect in psychotherapy refers to symptom exacerbation or negative psychological responses induced by contextual, interpersonal, or expectancy-related factors rather than the therapeutic content itself. These effects may emerge from subtle cues in therapist language, treatment framing, or patient beliefs. What passes for a “bad reaction to medication” may sometimes be a bad reaction to the information about medication.
Psychotherapy’s Inconvenient Truth
Perhaps nowhere does Evans’ framework cut more provocatively than in its implications for psychological treatment. He asks whether something like psychotherapy may still be a benefit even though it may only, at best, be able to claim a placebo effect. This is a sharper question than it sounds. Psychotherapy is effective and the evidence for this is robust and consistent. But research into common factors consistently shows that its effectiveness may have less to do with the specific technique employed and more to do with the relationship in which that technique is embedded.
Research in a number of areas documents that expectations have a strong influence on experience. The burgeoning research on the effects of placebos also documents the importance of expectations, and placebos have robustly shown to alter reported experience alongside demonstrating physiological and neural mechanisms.
Psychotherapist Bruce Wampold’s influential contextual model identifies empathy, therapeutic alliance, cultural adaptation, and patient expectations as the primary drivers of therapeutic change – not the specific brand of therapy. Specificity is reported to account for a mere 1% of the overall therapeutic outcome. Despite the absence of specificity in psychotherapy, meta-analyses have demonstrated that clients receiving psychotherapeutic treatment are 80% better off than clients who do not receive treatment.
If that is true, then part of psychotherapy’s power overlaps with what placebo research reveals: structured expectation, relational safety, meaning, ritual and the mobilisation of the patient’s own regulatory resources. This does not make psychotherapy fraudulent. It makes it biologically real in a way that defies the drug-model template and may demand different frameworks for understanding what treatment actually is.
The Psychedelic Paradox
The same questions now haunt perhaps the most exciting frontier in contemporary psychiatry: psychedelic-assisted therapy. Psilocybin, MDMA, and ketamine have generated promising clinical results for depression, PTSD, and addiction, and their proponents speak of near-miraculous transformations. But the field faces a methodological problem that is, in a sense, Evans’ problem writ large and urgent.
Blinding in many psychedelic trials is fragile, and in high-dose studies often functionally compromised. Thus, positive expectancy effects associated with receiving psilocybin – as well as negative expectancy associated with receiving placebo – are likely; particularly given that those who are suspicious of psilocybin therapy are unlikely to volunteer for a clinical trial. Psychedelics themselves may be pharmacological moderators of the very expectancy effects we seek to measure.
This is a recursive knot. In ordinary drug trials, the patient might not know whether they’ve received the drug or the sugar pill. In a psilocybin trial, almost everyone knows – and their pre-existing beliefs, hopes, and cultural frameworks about the transformative power of psychedelics become impossible to disentangle from the drug’s pharmacological action. In a four-week self-blinding study of psychedelic microdosing, initial improvements in well-being and other psychological outcomes were also seen in the placebo group, and no reliable between-group differences remained. The molecule and the meaning are entangled, and any honest clinical science of psychedelics must grapple with that.
The Open Label Secret
The most destabilising recent development in placebo research has been the emergence of open-label placebos, which are inert pills administered with full disclosure. Patients are told explicitly: this pill contains no active ingredient, but research shows these pills can still help through your body’s own healing processes – and in some trials, particularly in conditions such as IBS, they do appear to help. Placebo effects can be established by an individual’s belief in the effectiveness and positive outcomes of a treatment, and the main working mechanisms include associative learning processes such as conditioning, and the adjustment of expectations.
This dissolves a key assumption foundational to most ethical critiques of placebo use – that deception is a necessary feature of the effect. You can know you are receiving an inert substance and still respond to it. In this sense, the effect is not purely about false belief; it is activated by context, relationship, expectation, and the body’s sophisticated interpretation of social and symbolic signals. The ritual of receiving treatment, even a transparently empty one, speaks to something below the register of conscious reasoning.
Evans could not have known about this research when he wrote his book, but his framework anticipates it with uncanny accuracy. The acute phase response he proposes as the substrate of placebo healing is not conscious. It does not require belief in the naive sense of deliberate conviction, it requires only the right signals including warmth, attention, care, and ceremony, to shift the body’s resource allocation toward recovery.
The Limits Of Belief
What makes Placebo: Mind Over Matter endure beyond its moment, and what makes it worth returning to alongside the research that has since filled in its outline, is that it holds two truths simultaneously without collapsing into either. Belief matters enormously, but belief has its limits. The book’s deepest provocation is not merely scientific. It is philosophical: our entire framework for distinguishing “real” from “not real” treatments rests on a tacit assumption that active and placebo effects are separable, that mechanism and meaning are orthogonal. Evans’ research suggests they are not.
This is disquieting for everyone. For those who want medicine stripped of all mystery, it suggests that you cannot optimise treatment down to pure pharmacology without losing something clinically real. And for those who want to liberate healing from materialism entirely, including the faith healers and the quantum consciousness crowd – Evans is equally ungenerous: the body’s self-healing apparatus is not infinite, is not responsive to wishful thinking alone, and does not bend to the kind of metaphysical demand that alternative realities typically sell.
The book still matters because it asks the right kind of question: not “is it all in the mind?” but “what kind of organism has a mind that can alter bodily experience through meaning?” That cuts through both medical reductionism and wellness inflation. The placebo effect is not mind over matter, it is meaning through matter: a biology of meaning, a pharmacology of relationship, and an immune system that reads social cues. In medicine as in life, how something is done matters as much as what is done. That is both more modest and more extraordinary, and we have barely begun to take that seriously.
