Advances in biotechnology and the chemical synthesis of peptides have made biopharmaceuticals and synthetic peptide drugs viable pharmaceutical compounds today and an important source for tomorrow's drugs and therapies. Unfortunately, also falsiﬁcations and counterfeit versions of these powerful and promising drugs are oﬀered illegally via the internet. Since these falsiﬁed preparations are produced outside the legally required quality systems, end-users have no guarantee regarding the eﬃcacy and safety of these products. Although falsiﬁed samples of biotherapeutics were already analysed, looking at a speciﬁc aspect of their quality or identity, no systematic studies have been performed regarding the presence of diﬀerent impurities or possible contaminations. Therefore, in order to obtain a better understanding of the potential health risks related to the usage of falsiﬁed polypeptide drugs we performed a systematic screening of the ten most frequently encountered falsiﬁed peptide drugs on the Belgian market acquired from three diﬀerent suspected illegal internet pharmacies. The screening incorporated the analysis of the active pharmaceutical ingredient (API), API-related impurities, small molecule contaminants (deﬁned as organic small molecules not belonging to the other categories), elemental impurities and residual solvents. This comprehensive study showed that these type of falsiﬁed drugs not only have a high variation in amount of drugs per unit and a low purity (ranging between 5% and 75% for cysteine containing peptides), but also contained the known toxic class one elemental impurities arsenic (As) and lead (Pb). One sample was contaminated with Pb while multiple samples were found with concentrations up to ten times the ICH toxicity limit for parenteral drugs. Subsequent speciation of As conﬁrmed the elevated concentrations for As and demonstrated that all As was present in the more toxic inorganic form. Together with the (sometimes) high amount of peptide impurities and the inherent dangers associated with the use of unauthorized peptide drugs (such as doping peptides or preclinical drugs) this study conﬁrms the reported potential health risks patients/users take when resorting to falsiﬁed peptide drugs. Moreover, the presence of the carcinogen As and the known accumulation in human tissues of Pb raises questions about potential sub-acute to chronic toxicity due to the long term administration of these falsiﬁed peptide drugs.