JMIR Publications

ABSTRACT

Background:

Digital mental health approaches offer a novel means to monitor and reduce harms associated with substance use in daily life. However, limited evidence exists on their application to methamphetamine (METH) use, particularly regarding individual variability in physiological responses and psychological conditions.

Objective:

This study aimed to explore inter- and intra-individual differences in craving, emotion, and heart rate associated with METH use, using data collected from a wearable device (Fitbit) and a mobile-based self-monitoring application.

Methods:

Participants were individuals with METH use disorder receiving outpatient treatment in Japan. Seven participants who used METH during an 8-week observation period were included in the analysis. Physiological data, including heart rate and sleep patterns, were collected using Fitbit devices, while daily self-reported METH use, craving intensity, and emotional status were recorded via a mobile application. After syncing the data, we visualized and summarized individual METH use patterns in detail. Correlations between physiological/psychological indicators and the frequency of METH use per day were analyzed. In addition, heart rate trends before and after METH use events were evaluated using a linear mixed effects model, and both inter-individual and intra-individual variability were also assessed.

Results:

Patterns of METH use varied widely across participants, with it most commonly occurring in the morning or at night, regardless of the day of the week. Craving and negative emotions were frequently reported on METH-use days and were positively correlated with the number of METH use episodes per day. Participants who used METH more frequently exhibited relatively higher resting heart rates. Following METH use, the heart rate increased significantly and remained elevated for up to 9 hours. Sleep duration and frequency were reduced or absent on METH-use days. Approximately 64% of the variance in heart rate was attributable to inter-individual differences, while 12% reflected variability across events within the same individual.

Conclusions:

This study demonstrates the feasibility and value of using digital tools to examine physiological responses and psychological conditions associated with METH use in real-world settings. Persistent cardiovascular activation and disrupted sleep highlight the potential risks of long-term METH use. Individual differences in heart rate responses, craving, and emotional states underscore the importance of personalized intervention strategies. Integrating real-time self-monitoring, notifications for elevated heart rate, and online cognitive behavioral therapy into digital therapeutic interventions may improve health outcomes for individuals with METH use disorder.