Trends and transition dynamics of heated tobacco product use in Japan, 2015-2025: a repeated cross-sectional and longitudinal study.

BACKGROUND

Heated tobacco products (HTPs) diffused rapidly in Japan, but transition dynamics remain unclear. We examined trends in HTP use and routes underlying its growth.

METHODS

Using data from the Japan Society and New Tobacco Internet Survey, 2015-2025, we estimated weighted prevalence of HTP use (N = 161,583). Sex- and age-standardised prevalence was used to estimate segmented trends with a 2018 knot. Among respondents observed in consecutive years (93,540 pairs), we fitted a multinomial transition model across five states (Never, Non-current, Cigarette-only, HTP-only, and Dual use) and decomposed changes in standardised HTP prevalence into four categories: uptake from Never/Non-current states, switching from Cigarette-only to HTP, switching back to Cigarette-only, and exit to Non-current use.

FINDINGS: Weighted HTP prevalence increased from 0.1% to 14.9% during 2015-2025. Standardised prevalence rose sharply through 2018 (3.33 percentage points/year) and more gradually thereafter (0.92 percentage points/year). Transition probabilities showed post-2018 persistence of HTP-only/Dual use (67.9% and 57.0%, respectively). In the longitudinal decomposition, mean annual entry into HTP use increased from 2.16 percentage points before 2018 to 3.48 after 2018, while mean annual exit changed from -0.39 to -2.30. After 2018, entry from Non-current states increased markedly, whereas contributions from Never states were smaller and switching from Cigarette-only to HTP remained substantial.

INTERPRETATION: HTP use in Japan shifted around 2018 from rapid expansion to slower but sustained growth. Within the transition-eligible sample, later growth reflected multiple dynamics-including continued cigarette-to-HTP switching, persistence within HTP-using states, and increasing uptake from Non-current states-rather than cigarette substitution alone.

FUNDING: Japan Society for the Promotion of Science KAKENHI (25H01079).