Counterfeit thyroid medications: A comprehensive analysis of the composition of products seized by law enforcement using liquid chromatography coupled with mass spectrometry.

Drug counterfeiting is a global public health challenge affecting both developed and developing countries. This study reports the first comprehensive quality assessment of falsified medicinal products containing thyroid hormones (liothyronine and levothyroxine) seized from two illegal manufacturing facilities in Poland, from which counterfeit products were distributed across Europe. Qualitative and quantitative analyses of the declared active ingredients, along with identification of pharmacologically active contaminants, were performed using high-performance liquid chromatography coupled with mass spectrometry. The results revealed poor product quality and a substantial potential health risk. Trace levels of undeclared substances-including anabolic agents, hormones and metabolic modulators, diuretics and masking agents, phosphodiesterase type 5 inhibitors, and drugs of abuse-provided forensic evidence linking counterfeit pharmaceutical production to organized drug trafficking, while not constituting a direct pharmacological threat. The primary risk arose from incorrect and highly non-uniform dosing of the declared active compounds, in some cases exceeding 600 % of the labeled dose, thereby critically compromising treatment safety and efficacy.