What Is the Placebo Effect, and Why Can It Work Even When the Patient Knows They're Not Taking a Real Drug?

The placebo effect is a real improvement in a person's symptoms after receiving a treatment with no therapeutic active ingredient, driven by expectations, prior conditioning and the doctor-patient relationship. Surprisingly, studies show it can work even when the patient knows they are taking a placebo, a phenomenon known as open-label placebo.

How does the biological mechanism work?

It's not just "imagination" or a trick. When a person expects relief, the brain activates real neurochemical pathways:

• Endorphin release: Natural painkillers that reduce pain perception.
• Dopamine release: Improves motivation, movement (key in Parkinson's) and the sensation of reward.
• Endocannabinoid system: Regulates pain, inflammation and mood.
• Reduced anxiety: Decreases activity in the amygdala and the anterior cingulate cortex, areas linked to the suffering caused by pain.

The two main psychological pillars

Conscious expectation

The belief that a treatment will work triggers the mechanisms described above. The doctor's verbal cues ("this will relieve you"), the color and size of the pill, the clinical setting and the professional's empathy all shape that expectation.

Pavlovian conditioning

The body learns through association. If in the past you took a real painkiller (unconditioned stimulus) and felt relief (unconditioned response), the ritual of taking a pill (conditioned stimulus) eventually generates relief on its own (conditioned response), even if the pill is made of sugar.

The case of open-label placebos

For decades it was thought that a placebo required deception. Recent clinical trials in conditions such as irritable bowel syndrome, chronic lower back pain, cancer-related fatigue or allergies have shown that giving placebos while explicitly telling the patient: "This is a placebo, it has no medication, but it may help you through the placebo effect" produces significant improvements compared with no treatment at all.

This suggests that the therapeutic ritual, trust in the professional and conscious self-suggestion are enough to activate the brain's internal pharmacy.

Factors that boost the response

• Doctor-patient relationship: Empathy, active listening and validation of suffering amplify the effect.
• Treatment characteristics: Injections tend to produce a stronger effect than pills; large pills more than small ones; "strong" colors (red, orange) for stimulants and "calm" colors (blue, green) for sedatives.
• Cost and brand: Expensive or well-known brand-name placebos work better than cheap generics because of the expectation of higher quality.

The flip side: the nocebo effect

This is the evil twin. If a patient expects adverse effects (from reading the package insert or from alarmist warnings), their brain can generate real pain, nausea, dizziness or skin rashes with no pharmacological cause. Careful medical communication is key to minimizing it.

Ethical and clinical implications

Understanding the placebo effect isn't meant to justify prescribing sugar instead of effective drugs, but rather to:

• Optimize the effectiveness of real treatments by strengthening trust and communication.
• Design more rigorous clinical trials (with active placebo groups).
• Explore open-label placebo-based therapies for conditions where drugs fail or cause serious side effects.