The following factors were included as covariates for potential confounders or risk factors: sex (male or female), grade (7th, 8th, 9th, 10th, 11th, or 12th), academic performance (high, middle, or low), area of residence (metropolitan, urban, or rural), residence type (living with or without family), economic status (high, middle, or low), subjective health condition (healthy, normal, or unhealthy), physical activity over 1 h and five times per week (yes or no), drinking experience (yes or no), smoking status (never, ex-smoker, or current smoker), sleep satisfaction (satisfied, regular, or unsatisfied), stress perception (high, middle, or low), depressive symptoms in the past 12 months (yes or no), and year (2020, 2021, 2022, or 2023)
Health 12 , 100686 (2020)
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When you smoke or consume nicotine through other means regularly, your brain gets used to having nicotine around to keep these feel-good chemicals at high levels