Over time, the perception of placebos has evolved from being considered inert treatments to active components in clinical research. This shift has been driven by advances in neuroscience, which have uncovered the biological processes underlying placebo effects. Understanding these mechanisms provides a scientific foundation for the historical observations of their therapeutic potential.

One of the most significant advances in placebo research has been the discovery of specific neurobiological pathways activated by placebo treatments. Recent studies using advanced brain imaging techniques such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have shown that placebo-induced changes in brain activity are not limited to psychological “tricks” but involve tangible biological processes. For example, a study published in Nature Neuroscience found that placebo treatments can modulate emotions [41], while research in Brain highlighted that placebo effects are genuine psychobiological phenomena attributable to the overall therapeutic context, with evidence showing that placebo effects can occur in clinical practice, even without the administration of a placebo [42].

One notable study demonstrated that placebos activate the nigrostriatal pathway, a critical component of the brain’s dopamine system. Finnis et al. found that patients who believed they were receiving dopamine-enhancing medication experienced a real release of dopamine [13]. Nezer et al. examined how placebo treatments affect brain systems involved in affective processing, revealing that placebo treatments led to significant analgesia in response to conditioned thermal pain, which also generalized to unconditioned mechanical pain. This suggests that placebo-induced changes in brain activity extend beyond psychological factors, involving tangible biological processes [43]. Moreover, placebo treatments in patients with chronic pain have been shown to trigger the body’s natural pain-relieving systems, such as endogenous opioids and endocannabinoids. Other neuromediators, such as oxytocin, vasopressin, and noradrenaline, are also released during a placebo response (Figure 3) [20].

Furthermore, in patients with Parkinson’s disease, placebo treatments have been shown to activate the dopaminergic system, offering insights into the neurobiological mechanisms of placebo effects. In a study on Parkinson’s patients, placebo treatments induced dopaminergic responses, leading to symptom improvement and an increase in dopamine release, particularly in regions involved in motor control [44].

Placebo-induced pain modulation, as revealed by a meta-analysis by Atlas and Wager, consistently shows reductions in brain activity within regions crucial for pain processing, such as the left anterior, mid, and posterior insula, left putamen, and left amygdala. Simultaneously, placebo effects are associated with increased activity in areas involved in cognitive and affective regulation, including the pregenual anterior cingulate cortex (pgACC), medial orbitofrontal cortex (mOFC), ventromedial striatum, and anterior insula. These findings highlight the dual role of placebo in both reducing pain perception and enhancing regulatory mechanisms through expectancy-driven processes [45]. Additionally, a meta-analysis by Yeung et al. found that placebo treatment significantly improved perceived sleep onset latency, total sleep time, and global sleep quality in insomnia patients. However, no effect was observed on objective sleep onset latency, likely due to limited data. The placebo effect was consistent across various subjective measures, emphasizing the importance of subjective outcomes in insomnia treatment [46].

A study by Puviani and Rama proposed a quantitative model suggesting that the placebo response is driven by unconditioned stimulus (UCS) revaluation. This model indicates that the brain updates its response to a substance based on new information, contributing to the placebo effect [47].

These findings clearly demonstrate that placebos are not mere “shams” or “tricks”. The placebo effect transcends mental factors and involves physical processes in the brain and body.

Patient perception and expectations are fundamental to the efficacy of placebo treatments. Numerous studies have confirmed that positive expectations significantly enhance the placebo response, particularly in conditions involving pain management, depression, neurological function, and surgical recovery [17,42,48]. In a systematic review of surgical interventions, Vase and Wartolowski found that when patients expect their surgery will be successful, they are more likely to report pain reduction, both in sham and surgery groups [15].

A 2014 study by Kam-Hansen et al. demonstrated that the labeling of a treatment significantly influences its effectiveness, with both placebos and real medications showing improved efficacy when labeled “positively” (labeled with the name of a known medication, Maxalt). Further supporting the power of expectation, they found that Maxalt labeled as a placebo was no more effective than a placebo labeled as Maxalt [49].

Frisaldi et al. recently performed a pilot correlational study consisting of patients beginning immunosuppressive therapy for myasthenia gravis. Seventeen patients were assessed at baseline to determine their quantitative myasthenia gravis score (QMG), as well as their expected side effects and state anxiety. The study found that state anxiety moderated pre-treatment negative expectations, which were correlated with the fulfillment of those side effects [47].

Placebo treatments do not rely solely on conscious expectations but also on unconscious associations and expectations. There is an inherent belief that when seeking medical services, one’s health will improve. This expectation is shaped by sensory cues and behaviors commonly associated with medicine—signals to the brain indicating that treatment is imminent. Clinical settings, with their characteristic sights, sounds, and smells, interactions with professionals, and medical attention, have the power to activate the body’s natural healing processes [19,20,50].

The placebo effect does not operate in isolation; it can enhance the effectiveness of active treatments. The placebo effect arises from patient–practitioner interactions, sensory experiences, and the patient’s belief in the treatment process. By understanding and leveraging these factors, we can enhance the effects of both placebo and true medications, which could lead to reductions in medication doses, shorter treatment durations, increased patient safety, fewer side effects, and even reduced costs [33,45,49]. The effect of the placebo comes from patient–practitioner interactions, sensory experiences, and the patient’s belief in the treatment process. By understanding, and utilizing these factors, we can heighten the effects of both placebo and true medication, it is truly a shame we have not already carried this out. It could allow for reductions in medication doses and treatment duration, among other potential changes, leading to increased patient safety, decreased side effects, and even decreased costs [51,52].

Figure 3 depicts the contrasting neuromediator profiles associated with the placebo and nocebo responses, represented as a balance scale. The placebo response is characterized by an increased release of endogenous opioids, endogenous cannabinoids, dopamine, oxytocin, vasopressin, and noradrenaline. In contrast, the nocebo response is associated with reduced levels of endogenous opioids, endogenous cannabinoids, and dopamine, accompanied by increased release of cholecystokinin. These neuromediators contribute to the physiological and psychological effects observed during placebo and nocebo responses.