1. World Population Ageing, United Nations (2017),http://www.un.org/en/development/desa/population/publications/pdf/ageing/WPA2017_Highlights.pdf. Accessed 10 Aug 2020.
2. Community-oriented primary care, Ministry of Health, Labour and Welfare, Japanese Government. URL: https://www.mhlw.go.jp/stf/seisakunitsuite/bunya/0000080850.html. Accessed 3 Jan 2023.
3. Bruera E, Paice JA. Cancer pain management: safe and effective use of opioids. Am Soc Clin Oncol Educ Book. 2015;35:e593–9.
4. Kurita GP, Kaasa S, Sjøgren P. Opioid Analgesics. In: Bruera E, Higginson I, von Gunten C, editors. Textbook of Palliative Medicine and Supportive Care. 2nd ed. Boca Raton, FL: CRC Press Taylor and Francis Group; 2015. p. 395–408.
5. Death causes by sex, Vital statistics (2018), Ministry of Health, Labour and Welfare, Japanese Government. URL: https://www.mhlw.go.jp/toukei/saikin/hw/jinkou/kakutei18/dl/10_h6.pdf. Accessed 3 Jan 2023.