The occurrence of 22 drugs of abuse, their metabolites, and the alcohol metabolite ethyl sulphate was investigated in raw sewage samples collected during the non-touristic season from three sewage treatment plants (STPs), which serve different sizes and types of population in the Greek island of Lesvos. Using the sewage-based epidemiology approach, the consumption of these substances was estimated. Five target analytes, cocaine (COC), benzoylecgonine (BE), 3,4-methylenedioxymethamphetamine (MDMA), 11-nor-9-carboxy-delta-9-tetrahydrocannabinol (THC-COOH) and ethyl sulphate (EtS) were detected at concentrations above their limit of quantification, whereas the rest eighteen target compounds were not detected. THC-COOH was detected in most of the samples with concentrations ranging between < 20 and 90 ng L^− 1, followed by EtS (range < 1700–12,243 ng L^− 1). COC, BE, and MDMA were present only in the STP that serves Mytilene (the main city of the island), at mean concentrations of 3.9 ng L^− 1 for COC (95% CI: 1.7–6.1), 9.4 ng L^− 1 for BE (95% CI: − 1.6–23) and 3.2 ng L^− 1 for MDMA (95% CI: 1.2–5.1). Back-calculations to an amount of used substance indicated more intense use of drugs among city population than rural and University population with average values of 9.5 and 1.2 mg day^− 1 per 1000 inhabitants for COC (95% CI: − 1.43–20.4) and MDMA (95% CI: 0.52–1.85), respectively, and 2.8 g day^− 1 per 1000 inhabitants for tetrahydrocannabinol (THC) (95% CI: 2.4–3.1), the active ingredient of cannabis. Alcohol consumption was observed to be higher in the city population (5.4 mL pure alcohol per day per inhabitant) than in the rural population (3.4 mL pure alcohol per day per inhabitant), but the difference was not statistically significant. Consumption of THC differed significantly among the three STPs.