Reasons for continued usage of ENDS: Differences by device and liquid characteristics among US adults.

Introduction: Motivations for using electronic nicotine delivery systems (ENDS) include quitting or reducing cigarette smoking, flavor, and addiction. This study examines whether the primary reason for continued ENDS usage changes over time, and its association with device and liquid characteristics.

Methods: Data are from a longitudinal cohort study and include 526 US adults (≥21 years) using ENDS frequently (≥5 days/week) as self-reported, and uploaded photos of their most used ENDS devices and liquids and self-reported primary reason for continued ENDS usage in wave 2 (December 2020-April 2021) and wave 5 (February-April 2023). Device-liquid grouping was defined by device (disposable/disposable pod/refillable pod/tank, adjustable/no adjustable settings) and liquid (salt/freebase) characteristics. A device was classified as having adjustable settings if it allowed users to modify the power, coil, or airflow. Data were analyzed using multivariable logistic regressions and McNemar tests.

Results: From wave 2 to 5, the primary reason for continued ENDS usage significantly changed, with more participants reporting addiction (29.2% vs 34.6%, p<0.001); and significantly more participants used disposable devices (salt, no adjustable settings) (7.9% vs 25.2%, p<0.001). Compared to those using tanks (freebase, adjustable settings), participants using devices with nicotine salt liquids were more likely to report addiction (AOR>2; 95% CI: 1.12-8.19); and participants using disposable devices (salt, no adjustable settings) were less likely to report quitting/reducing smoking as the primary ENDS use reason after controlling for smoking status and sociodemographic characteristics (AOR<0.6; 95% CI: 0.14-0.995).

Conclusions: Over a 2.5-year period, the proportion of participants continuing to use ENDS at least 5 days/week because of addiction grew, and participants' motivations varied by device-liquid grouping. Restrictions on nicotine salts may disproportionately impact those using ENDS because of addiction; and regulations targeting tanks with freebase liquids may disproportionately impact those using ENDS for smoking cessation/reduction.