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Impact of the 2018 Japan Floods on benzodiazepine use: a longitudinal analysis based on the National Database of Health Insurance Claims



Natural disaster has an impact on mental health. The 2018 Japan Floods, which took place in July 2018 were one of the largest water disasters in Japan’s recorded history. We aimed to evaluate the change in the number of benzodiazepine prescriptions by physicians before and after the disaster.


A retrospective cohort study based on the National Database of Health Insurance Claims was conducted in the flood-stricken areas between July 2017 and June 2019. The subjects were divided between victims and non-victims according to certification by local governments. Members of both groups were then categorized into three groups based on their pre-flood use of benzodiazepines: non-user, occasional user, and continuous user. Difference-in-differences (DID) analysis with a logistic regression model was conducted to estimate the effect of the disaster among victims by comparing the occurrence of benzodiazepine prescriptions before and after the disaster.


Of 5,000,129 people enrolled, 31,235 were victims. Among all participants, the mean prescription rate for benzodiazepines in victims before the disaster (11.3%) increased to 11.8% after the disaster, while that in non-victims (8.3%) decreased to 7.9%. The DID analysis revealed that benzodiazepine prescription among victims significantly increased immediately after the disaster (adjusted ratio of odds ratios (ROR) 1.07: 95% confidence interval 1.05–1.11), and the effect of the disaster persisted even 1 year after the disaster (adjusted ROR 1.2: 95% confidence interval 1.16–1.24).


The flood increased the number of benzodiazepines prescriptions among victims, and the effect persisted for at least 1 year.

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Data availability

This data of this research was obtained from the National Database of Health Insurance Claims and was permitted to be used by the Ministry of Health, Labor and Welfare.


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Authors and Affiliations



All authors contributed to the development of this manuscript. YO was responsible for study design, analysis, interpretation of data and writing of the draft. SY contributed to data collection, analysis and interpretation of data and SaK assisted with the analysis and interpretation of data. MM supervised the whole study by contributing to the study design, data collection, interpretation of data and writing of the draft. SoK and SI contributed to the interpretation of data and writing of the draft. All authors have read and approved the final version of this manuscripts.

Corresponding author

Correspondence to Yuji Okazaki.

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The authors declare that they have no competing interests.

Ethical approval

The requirement for informed consent was waived because the anonymous data of National Database of Health Insurance Claims was used in this study.

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Okazaki, Y., Yoshida, S., Kashima, S. et al. Impact of the 2018 Japan Floods on benzodiazepine use: a longitudinal analysis based on the National Database of Health Insurance Claims. Soc Psychiatry Psychiatr Epidemiol 57, 2411–2421 (2022).

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  • Natural disaster
  • Benzodiazepine
  • Epidemiology
  • Anxiety
  • Insomnia
  • Rural health services