Fig. 3

Patients consuming Tramadol and Heroin were grouped according to age. a The number of younger patients (<30 years) was over 2 times more than the older patients (≥30 years). The young users tend to use pharmaceutical opioid (57.6 %), in particular Tramadol. In contrast, older patients (>30 years) tend to use illicit opioid (22.6 %), in particular Heroin. b The amount consumed of Tramadol and Heroin per day across age groups