The Power of Expectancy in Healthcare

 

Hey team,

Lately, I’ve been deep into behavioral economics, especially the work of Daniel Kahneman, which highlights the consistent irrationalities in human decision-making. These patterns, while irrational, are often predictable, and nowhere are they more visible (or more costly) than in healthcare.

My interest in this stems from a broader curiosity about human behavior, how we often make decisions that seem illogical on the surface, yet follow systematic patterns that can be understood, anticipated, and even shaped to support better outcomes.

Today, I want to explore one piece of that puzzle: expectancy. Specifically, how it shapes our experience of medical treatment, including both its beneficial effects and trade-offs. I'll be organizing this around four key questions:

• What is expectancy?
• Where does it come from?
• What does it explain?
• Why does it matter?

So let’s start with the first question:

What Is Expectancy?

At its core, expectancy refers to our belief about the likelihood that a particular action or treatment will lead to a desired outcome. In healthcare, it’s about more than just "will this work?" It encompasses safety, necessity, identity, and our previous experiences.

The brain’s job is to predict. Afterall we live in an ambiguous world and we must constantly disambiguate in order to make sense of what's going on, even at the cost of some poor predictions. Whether it’s danger, pain relief, or healing, our minds are constantly forecasting. And those predictions change how our bodies react. And expectation is more than mere psychological, it’s physiological. It’s what makes placebos powerful and side effects sometimes feel worse before they even happen.

Where Do Expectations Come From?

Expectancy is not a single belief, it’s an intricate network formed through:

• Personal experience: Past successes (or failures) with treatments build our internal reference points.
• Observational learning: Watching others, especially people like us, respond to a treatment reshapes our own expectations. If a friend thrives on medication, we’re more likely to expect it will help us too. This is a double edge sword and after seeing a friend develop an unfortunate effect of a drug or supplement might prime us towards the same reaction.
• Verbal persuasion: What clinicians, influencers, or ads tell us can set powerful mental anchors. Phrases like "clinically proven" or "balances neurotransmitters" create frameworks through which we interpret sensations.
• Physiological interpretation: A racing heart could mean anxiety, or excitement. Our interpretation of bodily signals contributes to whether we anticipate relief or deterioration.
• Cultural narratives: Different cultures shape what treatments feel legitimate. Western medicine might prize pharmaceuticals; other traditions lean holistic. These beliefs are rarely based on hard pharmacology, they’re born of trust, identity, and social learning.
• Branding and presentation: Identical pills can feel different if one’s branded and expensive while the other is generic. Expectancy is malleable and packaging matters.
• Media and stories: Anecdotes spread faster than data. A vivid story about a side effect or a miracle cure can overshadow actual evidence.

These elements don’t work in isolation. They interact dynamically, sometimes amplifying each other. A friend’s experience might override your doubts; your cultural background might intensify how you interpret a doctor’s advice.

Hope, Belief, and the Nocebo Trap

Expectancy and hope are closely related and absolutely inseparable. Often, we want relief, and we believe we’ll get it. That’s how we get a placebo response. But when hope and belief diverge, things shift. If you hope (desire) a drug will help but expect (believe) it to cause nausea, you may feel sick before the medication even metabolizes. That’s the nocebo effect, when negative expectations generate real symptoms.

Placebo and nocebo responses remind us how powerful hope and expectancy can be. If you want some incredible case examples please read this article.

Does Expectancy Actually Change Outcomes?

Yes. Dramatically.

Let’s look at a few examples:

• In depression trials, placebo responses hover around 30%. Often, the actual drug outperforms placebo by only 10%. That means belief alone explains a huge portion of symptom relief. While many take this as proof antidepressants don’t work, I would argue that placebo and antidepressants effects don’t demonstrate additivity. See "Ordinarily Well” for more details.
• In a placebo pain study, using both placebos framed as "natural" and "pharmaceutical" researchers discover that: individuals who favor pharmaceuticals get more relief as compared to a naturally framed placebo, the same is true for individuals who favor "natural" products. Additionally the pharmaceutical placebo was reported to have more side effects than its ”natural“ counterpart.
• When patients switch from brand-name drugs to generics, they often report worse outcomes, even when the active compound is identical. Perception alters experience.
• In COVID-19 vaccine trials, 76% of systemic side effects were seen in the placebo arm as compared to the active vaccine.
• This pattern reflects a broader trend: psychogenic vaccine reactions are surprisingly well documented, particularly in group vaccination settings where individuals, influenced by observing others, may develop similar symptoms.
• Keep in mind that this is far from a comprehensive list and there always exists far more nuance.

Why This Matter

Understanding expectancy isn’t just a fun exercise, it has real, tangible implications for how we deliver care.

• Clinicians can ethically cultivate positive expectations to enhance outcomes without resorting to deception or peddling.
• Clinical trials can be designed to more accurately separate the true pharmacologic effects of a treatment from those driven by expectation.
• Public health messaging can become more nuanced, acknowledging both placebo and nocebo effects without invalidating personal experiences.
• Healthcare systems can be structured to assess the beliefs of both patients and providers, enabling more personalized, collaborative care plans that reflect comfort, evidence, and trust.
• And perhaps most importantly, we can foster open dialogue, acknowledging humility, biases and preferences while still grounding our choices in research and the strength of available evidence.

Expectancy is a tool we already rely on, consciously or not. By understanding it better, we can use it with purpose.

In short: belief is biology. The way we frame treatments, the stories we tell, and the narratives we inherit all shape healthcare outcomes in ways we’re only beginning to fully appreciate. Expectancy might not come in a bottle, but it’s no less powerful than the pills that do.