Treatment Expectations

Abstract

A treatment expectation is what a person anticipates a treatment will do: how much it will help, how fast, and at what cost. Cognitive psychology treats that anticipation not as a reporting bias but as a cause of the outcome in its own right. Response-expectancy theory holds that an anticipated change can produce the change it anticipates, and the placebo and nocebo literatures show the mechanism directly, with a positive expectation recruiting endogenous opioid and dopamine systems and even doubling a real drug's measured analgesia. Expectations are learned from instruction, experience, and observation, and can be deliberately optimized before treatment to improve outcomes. This article sets out what a treatment expectation is, how it is formed and measured, and why it is now treated as a modifiable clinical target.

Keywords: treatment expectation, response expectancy, placebo effect, nocebo effect, expectation optimization

What a Treatment Expectation Is

A treatment expectation is a person's anticipation of what a treatment will do: the degree of benefit they expect, the symptoms they expect to change, the speed of relief, and the side effects they expect to endure. It is a prediction about one's own future state, held before and during treatment, and it is shaped by what a clinician says, what the person has experienced before, what they have seen happen to others, and what the ritual of treatment signals.

The move that makes treatment expectation a topic in cognitive psychology rather than a footnote to clinical trials is this: the expectation is not merely a lens that colours how an outcome is reported. It is a cause that helps produce the outcome. Irving Kirsch's response-expectancy theory makes the claim precisely — the expectation of a non-volitional response (relief, nausea, calm) is itself a determinant of that response, so anticipating relief is part of what brings relief about (Kirsch, 1985). The anticipation and the outcome are not two readings of one thing; the first is among the causes of the second.

How Expectations Are Formed

Three routes build a treatment expectation, and they can act together. Verbal instruction is the fastest: telling a patient that a drug is a powerful analgesic, or that an infusion has been stopped, shifts expectation in seconds and shifts the outcome with it. Direct experience is the most durable: a treatment that helped before generates an expectation that it will help again, a conditioning route in which the treatment cues the learned response the way a conditioned stimulus cues a conditioned response. Observation is the social route: watching another person benefit, or suffer a side effect, transfers the expectation without any first-hand trial.

The conditioning and the conscious-expectation routes are distinct but interacting, and separating them is one of the field's central methodological problems. A comprehensive review by Price, Finniss, and Benedetti laid out the paradigms that pull them apart — manipulating instructions while holding conditioning history constant, and vice versa — and concluded that both contribute, with conscious expectation dominant for conscious outcomes such as pain and conditioning dominant for unconscious physiological responses such as hormone secretion (Price, Finniss, & Benedetti, 2008). Colloca and Benedetti had already drawn the same line, showing that verbally induced expectations and experimentally induced conditioning can produce placebo responses through partly separable mechanisms (Colloca & Benedetti, 2005).

The Biology of Expectation

The strongest evidence that a treatment expectation is a cause and not a commentary is physiological. Fabrizio Benedetti and colleagues established that the expectation of benefit recruits real neurochemistry: an expected analgesic engages endogenous opioid systems, so that blocking those receptors with naloxone blocks the expectation-driven relief, while an expected reward engages dopamine systems (Benedetti et al., 2005). The expectation does not describe the relief after the fact; it triggers the machinery that produces it.

Neuroimaging localized the effect. Tor Wager's fMRI studies showed that a placebo treatment — a treatment whose only active ingredient is the expectation it carries — changes activity in pain-processing regions during both the anticipation of pain and its experience, with decreases in the regions that code the sensory and affective dimensions of pain and increases in prefrontal regions during anticipation (Wager et al., 2004). A later synthesis traced how an expectation signal is translated into a change in the pain experience itself, separating the top-down expectancy from the bottom-up sensory input (Atlas & Wager, 2012).

The cleanest single demonstration manipulated expectation while holding the drug constant. Ulrike Bingel and colleagues infused the opioid remifentanil at a fixed rate and varied only what patients were told: with a positive expectation the measured analgesia roughly doubled, and with a negative expectation — telling patients the drug had been stopped when it had not — the analgesia was abolished, even though the same amount of active opioid was in the bloodstream throughout (Bingel et al., 2011). Expectation did not report the drug's effect; it set it.

Measuring Expectations

Because the expectation is the cause, measuring it precedes and predicts the outcome. The simplest instruments ask directly: how much relief a patient expects, on a numerical scale, and with what confidence. These prospective ratings predict recovery across a wide range of conditions — a systematic review by Mondloch, Cole, and Frank found that patients' recovery expectations predicted their actual recovery, independent of the treatment given, in the great majority of studies examined (Mondloch, Cole, & Frank, 2001). The anticipation measured at baseline forecasts the outcome measured later.

Two distinctions sharpen the measurement. The first separates expectation (what I think will happen) from desire (what I want to happen); the two diverge, and it is the expectation that carries the predictive weight. The second separates a response expectancy — an anticipated automatic reaction such as relief or nausea — from an efficacy belief about the treatment in general; response-expectancy theory predicts that only the former directly produces the anticipated response (Kirsch, 1985). Getting the construct right at the point of measurement is what lets a trial attribute an outcome to expectation rather than to the passage of time or the natural course of the illness.

The Nocebo Direction

Expectation is signed. A positive anticipation produces the placebo direction — relief, improvement, benefit — and a negative anticipation produces the nocebo direction: expected harm that materializes as real symptoms. The two are a single expectancy mechanism running in opposite directions, and the clinical review by Colloca and Barsky frames them exactly so, surveying how a positive treatment expectation is elicited and harnessed and how a negative one is provoked — often inadvertently, by the way side effects are described during informed consent — and how it drives real symptom production and treatment discontinuation (Colloca & Barsky, 2020).

The nocebo direction is why expectation cannot be treated as a free clinical bonus. The same instruction that can raise a positive expectation can, phrased differently, manufacture side effects that the pharmacology alone would not produce. The negative arm of Bingel's remifentanil study is a controlled instance: a verbal manipulation alone turned a working analgesic into a subjectively inert one.

Expectation as a Clinical Target

If a treatment expectation is a modifiable cause, it can be optimized on purpose. The translational question — minimize the placebo component, maximize it, or personalize it — was posed directly by Enck, Bingel, Schedlowski, and Rief, who argued that the expectation is a lever a trial or a clinic can deliberately raise or lower rather than noise to be controlled away (Enck et al., 2013).

The decisive clinical evidence is the PSY-HEART trial. Winfried Rief and colleagues randomized patients awaiting heart surgery to a brief preoperative intervention that optimized their expectations about the operation and recovery; the expectation-optimized group had better outcomes six months later, including less disability and a better return to work, than patients who received the same surgery and the same standard support without the expectation intervention (Rief et al., 2017). Expectation was not merely correlated with recovery — changing it changed the outcome, which is the standard a modifiable clinical target has to meet.

Figure

The figure shows the single mechanism running in both directions: the same pharmacological effect produces more, equal, or less experienced benefit depending only on the sign of the expectation.

Interactive Demonstrations

Three demonstrations build the construct from the inside: how expectation and pharmacology combine into one experienced effect, how a fixed drug swings with instruction alone, and how an expectation is updated — or defended — by the evidence of an outcome.

The first demo is the response-expectancy integrator. The experienced relief is a weighted blend of the drug's pharmacological effect and the patient's expectation; raising the expectation weight shows how much of the felt outcome the anticipation alone can carry.

The second holds the drug dose constant and varies only the instruction, reproducing the logic of the Bingel remifentanil study: the same opioid reads as doubled, normal, or absent relief depending on whether the patient expects benefit, nothing, or withdrawal.

The third shows expectation as a belief that updates across trials. A high learning rate lets each outcome revise the expectation toward reality; a high cognitive-immunization setting lets a prior negative expectation survive good outcomes, the pattern Kube and colleagues proposed for why some expectations fail to update.

Worked Example

Take a patient whose pain sits at 60 on a 0–100 scale and a treatment whose pharmacological effect is a fixed 20 units of relief. Model the experienced relief as R = D × (1 + k·E), where D = 20 is the drug effect, k = 1 is the expectation gain, and E is the signed expectation valence.

With a neutral expectation (E = 0), R = 20 × (1 + 0) = 20, so pain falls from 60 to 40 — the drug's own effect, nothing added. With a positive expectation (E = +1), R = 20 × (1 + 1) = 40, so pain falls from 60 to 20: the measured relief has doubled, though not one molecule more of the drug was given. With a negative expectation (E = −1), R = 20 × (1 − 1) = 0, so pain stays at 60: the same active drug now produces no felt relief at all.

The three outcomes — 40, 20, and 60 — come from one dose and three instructions. That is the qualitative result Bingel and colleagues measured with remifentanil, and it is the arithmetic behind the second demo: the expectation term, not the drug term, is what moves between the three conditions.

Discussion

Treating a treatment expectation as a cause rearranges several familiar problems. The placebo control in a clinical trial stops being an inert baseline and becomes an active expectation condition, which is why a drug can fail to beat placebo without being useless — both arms carry the expectation, and the expectation works. The informed-consent conversation stops being a neutral disclosure and becomes an expectation-setting intervention, with the nocebo direction as its cost. And the clinician's manner stops being bedside decoration and becomes part of the treatment's mechanism, because the instruction and the ritual are among the inputs that build the expectation.

The construct also has a boundary. Expectation is powerful for outcomes the brain can modulate top-down — pain, nausea, fatigue, mood, arousal — and far weaker or absent for outcomes it cannot, such as shrinking a tumour or clearing an infection. Response-expectancy theory predicts exactly this asymmetry: an expectation directly produces only responses that are to some degree under the influence of central, non-volitional control. The honest version of the clinical claim is therefore narrow and strong rather than broad and vague — expectation reliably moves the self-regulated outcomes, and the biology says why.

Current Directions

The active front has moved from proving that expectation matters to learning when it updates and how to optimize it deliberately. Kube, Rief, and Glombiewski proposed that persistent negative expectations in depression are maintained by cognitive immunization — a reinterpretation of disconfirming good outcomes that protects the prior expectation from revision — which reframes the clinical problem as one of expectation updating rather than expectation content (Kube et al., 2017). The integrative review by Petrie and Rief surveys how expectations, emotions, and brain mechanisms combine across the placebo and nocebo literatures and sets the agenda for the psychobiology of expectation (Petrie & Rief, 2019).

The translational thread is expectation optimization as a stand-alone intervention. The PSY-HEART result (Rief et al., 2017) has pushed trials to test brief, structured expectation-management procedures before surgery and drug treatment, and the current clinical reviews treat the deliberate shaping of expectation — maximizing the placebo direction, minimizing the nocebo direction — as a legitimate and measurable part of care rather than an ethical grey area (Colloca & Barsky, 2020).

Common Misconceptions

A placebo response means the symptom was never real.

The expectation-driven relief is produced by real endogenous opioid and dopamine activity and shows up as real changes in pain-processing regions. The symptom was real and so is the relief; the expectation is simply one of the causes (Benedetti et al., 2005).

Expectation only changes what patients say, not what happens.

Naloxone blocks expectation-driven analgesia, and the effect appears in brain imaging and in objective physiology, not only in self-report. A pure reporting bias could not be reversed by an opioid antagonist (Wager et al., 2004).

If it is just expectation, a stronger drug will always win.

Bingel's experiment held a real opioid constant and still abolished its measured effect with a negative expectation. Expectation and pharmacology combine; the drug does not simply override the anticipation (Bingel et al., 2011).

Expectation can cure anything if it is strong enough.

Expectation reliably moves centrally modulated outcomes such as pain, nausea, mood, and arousal, and does little to outcomes outside that control, such as tumour growth. The mechanism has a real and predictable boundary (Colloca & Barsky, 2020).

Glossary

Key Researchers

Fabrizio Benedetti

(University of Turin Medical School). Physiologist whose placebo-mechanism experiments established that an expectation of benefit recruits endogenous opioid and dopamine systems, turning treatment expectation from a nuisance variable into a measurable biological cause. Google Scholar · Wikipedia

Ulrike Bingel

(University Hospital Essen). Neurologist whose remifentanil experiment showed that a treatment expectation can double or abolish the measured effect of an active opioid. ORCID · Google Scholar

Luana Colloca

(University of Maryland, Baltimore). Physician-scientist who maps how positive and negative treatment expectations are learned and expressed, and how they can be harnessed in clinical pain care. Google Scholar · Wikidata

Irving Kirsch

(Harvard Medical School). Psychologist whose response-expectancy theory — that what a person anticipates becomes a cause of what happens — is the direct ancestor of the treatment-expectation construct. Google Scholar · Wikipedia

Winfried Rief

(University of Marburg). Clinical psychologist who led the randomized trials showing that optimizing patients' preoperative treatment expectations improves surgical outcomes. Google Scholar · Wikipedia

Tor D. Wager

(Dartmouth College). Cognitive neuroscientist whose fMRI studies gave the first direct brain evidence that a treatment expectation changes activity in pain-processing regions during both anticipation and experience. ORCID · Google Scholar · Wikipedia

Frequently Asked Questions

What is a treatment expectation?

It is what a person anticipates a treatment will do for them: how much it will help, how quickly, and with what side effects, held before and during the treatment. Cognitive psychology treats this anticipation as a cause of the outcome, not just a bias in how the outcome is reported.

How is a treatment expectation different from hope or desire?

Desire is what a person wants to happen; expectation is what they think will happen. The two often diverge, and it is the expectation, not the desire, that predicts and helps produce the outcome. Response-expectancy theory makes this the central distinction.

Does expectation really change the body, or just the report?

It changes the body. Expectation-driven analgesia is blocked by the opioid antagonist naloxone and shows up as altered activity in pain-processing brain regions, so it cannot be a pure reporting effect. A positive expectation recruits real endogenous opioid and dopamine activity.

What is the nocebo effect?

It is the negative direction of the same mechanism: a negative expectation producing real adverse symptoms. The way side effects are described during informed consent can inadvertently create them, which is why expectation is not simply a free clinical benefit.

Can a treatment expectation change how well a real drug works?

Yes. In a controlled experiment, a fixed infusion of the opioid remifentanil produced roughly doubled analgesia under a positive expectation and no measurable analgesia under a negative one, with the same amount of active drug present throughout.

Where do treatment expectations come from?

From three routes that can combine: verbal instruction, direct prior experience with a treatment, and observation of others. Instruction acts fastest, experience is the most durable, and observation transfers an expectation socially without a first-hand trial.

Can expectations be deliberately improved before treatment?

Yes. A brief preoperative intervention that optimized patients' expectations before heart surgery improved their outcomes six months later, which is the evidence that expectation is a modifiable clinical target rather than only a correlate of recovery.

Does expectation work for every condition?

No. It reliably moves outcomes the brain can modulate from the top down, such as pain, nausea, fatigue, mood, and arousal, and does little for outcomes outside that control, such as tumour growth or infection. The mechanism has a real and predictable boundary.

References

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