The DELIRIA-J research network has conducted multiple randomized controlled trials (RCTs),1–3 and several Japanese academic societies have developed clinical guidelines4 and consensus statements on delirium.5,6 Building on these and other Japanese contributions, the Japanese Delirium Society (JDS) has been established to unify clinical practice, research, and education. This manuscript describes the historical background, highlights representative scientific accomplishments by Japanese investigators, outlines the organizational structure of JDS, and summarizes recent international engagement with the American Delirium Society (ADS) and Australasian Delirium Association (ADA). JDS is positioned to strengthen national collaboration and to contribute to global delirium science and care.

Background: Delirium in Japan

Delirium is an acute and fluctuating disturbance of consciousness and cognition, affecting up to one in three hospitalized older adults. It is associated with prolonged hospital stays, increased morbidity and mortality, institutionalization, and higher healthcare costs.7–9 Despite its prevalence and impact, delirium is often under-recognized and undertreated in clinical practice.
Japan, with one of the world’s fastest aging populations, faces a particularly urgent challenge in addressing delirium. Elderly individuals frequently require complex care in perioperative, oncological, and intensive care contexts, making delirium prevention and management a national health priority.
Japan hosts more than 80 medical schools and a large network of general hospitals, with many clinicians and researchers actively engaged in delirium research. Over the past two decades, Japanese investigators have made significant contributions to the global evidence base, including pioneering randomized controlled trials,1–3 a systematic management program aimed at screening high-risk groups and preventing delirium,10 development of clinical guidelines, and translational work in biomarkers and neurophysiology.11–18 These activities set the stage for the formation of a dedicated national society.

Historical Foundations: DELIRIA-J

The roots of the Japanese Delirium Society can be traced to the establishment of DELIRIA-J, a nationwide research consortium that emerged in 2011. Following the 2005 U.S. Food and Drug Administration (FDA) warning against the use of atypical antipsychotics in dementia patients due to increased mortality risk, Japanese clinicians sought safer and more effective strategies to manage delirium.
In response, the Japanese Society of General Hospital Psychiatry released clinical guidelines on delirium management,6 which provided a crucial reference point for everyday practice. From this initiative, the DELIRIA-J network was launched, connecting approximately 40 hospitals across the country.
DELIRIA-J became a highly productive research collaboration, conducting landmark studies with direct clinical relevance. One of the most impactful contributions was the randomized controlled trial of ramelteon for delirium prevention, published in JAMA Psychiatry in 2014.1 This trial demonstrated a significant reduction in the incidence of delirium among hospitalized elderly patients. Subsequent trials explored other pharmacological options such as suvorexant2,3 and Yokukansan.19–22 Together, these studies positioned Japanese researchers at the forefront of global efforts to test preventive interventions.

Representative Scientific Contributions by Japanese Investigators

Japanese researchers have contributed substantially to the global understanding of delirium across multiple domains. In the area of pharmacological interventions, randomized controlled trials of ramelteon1 and suvorexant2 have provided robust evidence supporting novel preventive approaches, offering alternatives to traditional antipsychotic-based strategies. Japanese investigators have also developed and evaluated the DELirium Team Approach (DELTA) program, a systematic management program aimed at screening high-risk patients and preventing delirium, which demonstrated the feasibility and clinical benefit of a structured, team-based prevention strategy.10 In addition to these advances, Japanese team have pioneered the development of the bispectral EEG (BSEEG), a simplified point-of-care neurophysiological tool that enables rapid bedside detection of delirium and prediction of clinical outcomes.11–13 Complementary work in translational models has further demonstrated that rodent EEG alterations mirror those observed in humans, particularly under conditions of systemic inflammation, thereby providing mechanistic insights into delirium pathophysiology.14,23–25 More recently, genome-wide DNA methylation studies have begun to uncover epigenetic signatures of delirium, implicating immune and inflammatory pathways as critical biological substrates.15–18,26–31 Collectively, these contributions highlight the breadth of Japanese delirium research, spanning clinical trials, technological innovation, animal models, and molecular biology.

Establishment of the Japanese Delirium Society (JDS)

The momentum generated by DELIRIA-J and broader Japanese research culminated in the establishment of JDS. Leadership includes President (Y. Kishi), Vice-President (K. Hatta), Advisor (K. Nishimura), and Secretary (G. Shinozaki). The founding membership spans ~25 institutions, including the Juntendo University Nerima Hospital, Nippon Medical University Musashikosugi Hospital, Tokyo Women’s Medical University, Tottori University, Osaka Medical and Pharmaceutical University, National Cancer Center, and more.
Although psychiatrists represent the largest group, anesthesiologists, surgeons, nurses, pharmacists, researchers, and industry are included, reflecting delirium’s multidisciplinary nature. The JDS establish meeting was held during the annual meeting of the Japanese Society of General Hospital Psychiatry in November 2024 in Kumamoto.

Opportunities and Challenges for JDS

As with any newly established professional society, the Japanese Delirium Society faces both challenges and opportunities. A key challenge is the overlap with pre-existing organizations and meetings in Japan, which risks duplicating efforts and fragmenting the community. Ensuring sustainable funding is another pressing issue, as financial resources will be essential to support educational programs, annual conferences, and large-scale collaborative research initiatives. In addition, while psychiatrists currently form the core membership, expanding beyond psychiatry to fully incorporate anesthesiology, surgery, geriatrics, nursing, pharmacy, basic sciences, mental health officers of the Ministry of Health, Labour and Welfare, Japan, as well as active patient and public involvement, will be critical for building a truly multidisciplinary society. Such inclusivity is intended not only to advance clinical and scientific perspectives but also to address broader goals, including the reduction of healthcare costs and the sustainable maintenance of society. At the same time, JDS is uniquely positioned to seize important opportunities. Japan’s extensive hospital network offers an unparalleled platform for conducting national multicenter trials, thereby generating high-quality, generalizable data. The society is also well placed to strengthen ties with international partners, particularly the American Delirium Society, the European Delirium Association, and the Australasian Delirium Association, creating avenues for joint symposia, research collaborations, and trainee exchanges. Looking further ahead, JDS aspires to host a World Delirium Conference in Japan, which would showcase the nation’s contributions and establish it as a central hub for global delirium research and clinical innovation.

International Engagement

As above, JDS will value an international collaboration. In 2025, Japanese investigators contributed to ADS meetings in Nashville, TN, USA, presenting several high impact research projects, ranging from pharmacologic RCTs, molecular investigation of pathophysiology, rodent model using BSEEG, and also cellular and epigenetic work.31
JDS members also participated in the ADA DECLARED conference in Cairns, Australia, highlighting Pan-Pacific collaborations. Such meetings facilitate harmonization of methodologies and establish a framework for joint trainee exchanges and multicenter protocols.

Future Directions

The Japanese Delirium Society has outlined a set of strategic goals that balance immediate priorities with longer-term aspirations. In the near term, the society aims to build a national training pipeline that equips clinicians across disciplines with standardized tools for delirium prevention, detection, and management. This includes disseminating practical resources such as delirium novel screening tools developed through recent research, integrating order sets into electronic medical records to support routine practice, and promoting the adoption of common data elements across multicenter studies to enable large-scale data harmonization. Over the longer term, JDS seeks to elevate the methodological rigor of delirium research by supporting pragmatic trial designs that bridge effectiveness with implementation science. Parallel efforts will focus on advancing biomarker development, including physiological makers such as EEG as well as molecular markers such as epigenetic signals, to improve risk stratification and mechanistic understanding. Finally, the society intends to formalize international liaisons with the American Delirium Society, the European Delirium Association, and the Australasian Delirium Association, with the goal of co-developing consensus statements and launching joint multicenter trials. These initiatives position JDS to not only improve delirium care in Japan but also to make substantive contributions to the global scientific community.

Conclusions

The establishment of JDS represents a pivotal step for delirium science and care in Japan. By unifying education, research, and clinical activities, JDS will accelerate national progress while contributing to international networks. With robust past achievements1–3,11–18 and a clear roadmap, JDS is well positioned to contribute in delirium prevention, detection, and treatment.

Acknowledgments

We thank the clinicians, researchers, nurses, and institutions across Japan who contributed to delirium research and to the founding of JDS. We also acknowledge international colleagues for fostering a spirit of collaboration.