Background Some drugs impair tasks related to driving, and roadside drug testing remains an important tool for deterring driving under the influence of them.

Objective To assess the presence and concentration of methadone, and their combined use with other drugs (laboratory confirmation after the on-road screening) in Spanish drivers between 2011–2016.

Methods In Spain, roadside mandatory drug testing using saliva are carried out by the Traffic Police using Dräger DrugTest® 5000, DrugWipe®, or Alere™ DDS®2 Mobile Test System. For positive cases in the period covered, 65244, confirmation analysis and quantification of methadone using chromatographic techniques were performed. Statistical analysis was carried out with R programming language (3.4.1) and SPSS version 23.0.

Findings Methadone was confirmed in 4.1% of positive cases: these tested also positive to 6-acetylmorphine (heroin metabolite, 81.9%) and other illicit drugs, such as cocaine (80%) and cannabis (45%). Only in a minority of methadone positives (0.4%) cases no other substances were detected. Concentration values reached important levels (median 201.4 ng/mL) and there was a relationship with age (R-squared=0.1475, p<0.005).

Conclusions Poly drug use (heroin, cocaine, cannabis) was the rule in drivers with methadone positive confirmation analyses.

Policy implications As methadone is a physician prescribed medication, improving opioid prescription, promoting the use of less driving-impairing medications, and giving more clear information to patients (risk communication) is a need.

This work was supported by the Instituto de Salud Carlos III, Redes Temáticas de Investigación Cooperativa, Red de Trastornos Adictivos [grant RD16/0017/0006], co-funded by FEDER funds of the European Union: a way to build Europe.