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Although a large body of research shows that general cognitive ability is heritable and stable in young adults, there is recent evidence that fluid intelligence can be heightened with cognitive training. Many researchers, however, have questioned the methodology of the cognitive-training studies reporting improvements in fluid intelligence: specifically, the role of placebo effects. We designed a procedure to intentionally induce a placebo effect via overt recruitment in an effort to evaluate the role of placebo effects in fluid intelligence gains from cognitive training. Individuals who self-selected into the placebo group by responding to a suggestive flyer showed improvements after a single, 1-h session of cognitive training that equates to a 5- to 10-point increase on a standard IQ test. Controls responding to a nonsuggestive flyer showed no improvement. These findings provide an alternative explanation for effects observed in the cognitive-training literature and the brain-training industry, revealing the need to account for confounds in future research.

Author and journalist Melanie Warner takes readers on a vivid, fascinating journey through the world of alternative medicine. Crossing continents and sides of the debate, visiting prestigious research clinics and ordinary people's homes, she investigates the scientific underpinning for the purportedly magical results of these practices and reveals not only the medical power of beliefs and placebo effects, but also the range, limits, and uses of the surprising system of self-healing that resides inside us.

Placebo effect refers to beneficial changes induced by the use of inert treatment, such as placebo-induced relief of physical pain and attenuation of negative affect. To date,we know little about whether placebo treatment could facilitate social functioning, a crucial aspect for well-being of a social species. In the present study, we develop and validate a paradigm to induce placebo effects on social trust and approach behavior (social placebo effect), and show robust evidence that placebo treatment promotes trust in others and increases preference for a closer interpersonal distance. We further examine placebo effects in real-life social interaction and show that placebo treatment makes single, but not pair-bonded, males keep closer to an attractive first-met female and perceive less social anxiety in the female. Finally,we show evidence that the effects of placebo treatment on social trust and approach behavior can be as strong as the effect of intranasal administration of oxytocin, a neuropeptide known for its function in facilitating social cognition and behavior. The finding of the social placebo effect extends our understanding of placebo effects on improvement of physical, mental, and social well-being and suggests clinical potentials in the treatment of social dysfunction.

RationaleIs it possible to have a psychedelic experience from a placebo alone? Most psychedelic studies find few effects in the placebo control group, yet these effects may have been obscured by the study design, setting, or analysis decisions.ObjectiveWe examined individual variation in placebo effects in a naturalistic environment resembling a typical psychedelic party.MethodsThirty-three students completed a single-arm study ostensibly examining how a psychedelic drug affects creativity. The 4-h study took place in a group setting with music, paintings, coloured lights, and visual projections. Participants consumed a placebo that we described as a drug resembling psilocybin, which is found in psychedelic mushrooms. To boost expectations, confederates subtly acted out the stated effects of the drug and participants were led to believe that there was no placebo control group. The participants later completed the 5-Dimensional Altered States of Consciousness Rating Scale, which measures changes in conscious experience.ResultsThere was considerable individual variation in the placebo effects; many participants reported no changes while others showed effects with magnitudes typically associated with moderate or high doses of psilocybin. In addition, the majority (61%) of participants verbally reported some effect of the drug. Several stated that they saw the paintings on the walls “move” or “reshape” themselves, others felt “heavy… as if gravity [had] a stronger hold”, and one had a “come down” before another “wave” hit her.ConclusionUnderstanding how context and expectations promote psychedelic-like effects, even without the drug, will help researchers to isolate drug effects and clinicians to maximise their therapeutic potential.

Children and adolescents with major depressive disorder (MDD) appear to be more responsive to placebo than adults in randomized placebo-controlled trials (RCTs) of second and newer generation antidepressants (SNG-AD). Previous meta-analyses obtained conflicting results regarding modifiers. We aimed to conduct a meta-analytical evaluation of placebo response rates based on both clinician-rating and self-rating scales. Based on the most recent and comprehensive study on adult data, we tested whether the placebo response rates in children and adolescents with MDD also increase with study duration and number of study sites. We searched systematically for published RCTs of SNG-AD in children and/or adolescents (last update: September 2017) in public domain electronic databases and additionally for documented studies in clinical trial databases. The log-transformed odds of placebo response were meta-analytically analyzed. The primary and secondary outcomes were placebo response rates at the end of treatment based on clinician-rating and self-rating scales, respectively. To examine the impact of study duration and number of study sites on placebo response rates, we performed simple meta-regression analyses. We selected other potential modifiers of placebo response based on significance in at least one previous pediatric meta-analysis and on theoretical considerations to perform explorative analyses. We applied sensitivity analyses with placebo response rates closest to week 8 to compare our data with those reported for adults. We identified 24 placebo-controlled trials (2229 patients in the placebo arms). The clinician-rated placebo response rates ranged from 22 to 62% with a pooled response rate of 45% (95% CI 41–50%). The number of study sites was a significant modifier in the simple meta-regression analysis [odds ratio (OR) 1.01, 95% CI 1.01–1.02, p = 0.0003, k = 24) with more study sites linked to a higher placebo response. Study duration was not significantly associated with the placebo response rate. The explorative simple analyses revealed that publication year may be an additional modifier. However, in the explorative multivariable analysis including the number of study sites and the publication year only the number of study sites reached a p value ≤ 0.05. The self-rated placebo response rates ranged from 1 to 68% with a pooled response rate of 26% (95% CI 10–54%) (k = 6; n = 396). This meta-analysis confirms a high pooled placebo response rate in children and adolescents based on clinician ratings, which exceeds that observed in the most recent meta-analysis of placebo effects in adults (36%; 95% CI 35–37%) published in 2016. However, and similar to findings in adults, the pooled response rates based on self-ratings were substantially lower. In accordance with previous meta-analyses, we corroborated the number of study sites as significant modifier. In comparison to the recent adult meta-analysis, the substantially lower number of pediatric studies entails a reduced power to detect modifiers. Future studies should provide more precise and homogenous information to support discovery of potential modifiers and consider no-treatment—if ethically permissible—to allow differentiation between placebo and spontaneous remission rates. If these differ, practicing clinicians should facilitate placebo effects as an addition to the verum effect to maximize benefits. Further research is required to explain the discrepant response rates between clinician and self-ratings.

The importance of contextual effects and their roles in clinical care controversial. A Cochrane review published in 2010 concluded that placebo interventions lack important clinical effects overall, but that placebo interventions can influence patient-reported outcomes such as pain and nausea. However, systematic reviews published after 2010 estimated greater contextual effects than the Cochrane review, which stems from the inappropriate methods employed to quantify contextual effects. The effects of medical interventions (i.e., the total treatment effect) can be divided into three components: specific, contextual, and non-specific. We propose that the most effective method for quantifying the magnitude of contextual effects is to calculate the difference in outcome measures between a group treated with placebo and a non-treated control group. Here, we show that other methods, such as solely using the placebo control arm or calculation of a ‘proportional contextual effect,’ are limited and should not be applied. The aim of this study is to provide clear guidance on best practices for estimating contextual effects in clinical research.

ObjectiveTo investigate whether anxiety reductions attributed to healing crystals reflect placebo responses driven by conditioning and belief-related biases rather than specific therapeutic effects.MethodsIn a randomized, controlled study, 138 adults were classified as believers or nonbelievers in crystal efficacy and assigned to rose quartz (experimental) or a visually matched placebo. Participants followed a standardized 14-day protocol. Anxiety was assessed pre- and post-intervention with the Beck Anxiety Inventory and the Spanish Kuwait University Anxiety Scale. Multilevel analyses of variance (ANOVA) and Bayesian models were used to evaluate main effects, interactions, and evidence for treatment specificity.ResultsAnxiety reductions occurred only among believers, regardless of crystal assignment. No differences were detected between groups in primary outcomes, and improvements did not exceed the magnitudes typically associated with placebo responses. Bayesian estimates favored the null hypothesis for specific treatment effects. Preexisting belief strongly predicted perceived efficacy and symptom change, consistent with causal illusions plausibly shaped by conditioning mechanisms. Nonbelievers showed no reliable improvement.ConclusionHealing crystals did not demonstrate anxiolytic effects beyond those of the placebo. Symptom change was mediated by expectancy and conditioning, particularly in individuals inclined toward intuitive or magical thinking. Although nonspecific, context-dependent factors—such as elements of the therapeutic alliance—may amplify placebo responsiveness in clinical settings, these findings do not support attributing inherent therapeutic value to crystals. Future work should delineate how expectations, clinician-patient rapport, and related variables interact to shape placebo response and how such mechanisms might be ethically leveraged to enhance evidence-based care without promoting pseudoscientific practices.