Cocaine was the second most widely used drug in Europe in 2016, with 3.5 million consumers aged 15-64 years old. Adulterants are pharmacologically active substances developed for medical purposes, however, there is little knowledge about their influence in the human body when there is concomitant use with cocaine. The objective of this work was to validate a method that allows the identification, confirmation and quantification of cocaine adulterants in blood samples collected in vivo or post-mortem. The studied substances were atropine, phenacetin, hydroxyzine, ketamine, lidocaine and tetramisole. A retrospective study of the prevalence of these substances, as well as their relative concentrations, was made analysing 97 real blood samples previously tested positive for cocaine and/or its metabolites. The analytes of interest were extracted, using a simple method based on protein precipitation with frozen acetonitrile and further analysis by GC/MS. The method was fully validated in accordance with parameters and criteria implemented in the lab and SWGTOX recommendations (mean recovery: 94-115%; CV: 6.2-13%; BIAS: 2.7-7.8%). 31 samples were positive for adulterants: phenacetin (19%), tetramisole (15%), lidocaine (8%) and hydroxyzine (1%). Concentrations were higher in post-mortem samples for all compounds analysed. Lidocaine was more prevalent in samples collected in vivo whereas tetramisole was present almost exclusively in post-mortem samples. Phenacetin was evenly distributed between post-mortem and in vivo samples. The validated method allows rapid, precise, accurate and economic analysis of selected compounds and requires smaller sample aliquots which can be important in post-mortem cases. The information collected can be important in future studies of correlation between the presence of adulterants and cocaine toxicity.