Application of screening methods for weight-loss compounds and identification of new impurities in counterfeit drugs.

With the increasing prevalence of obesity, the use of counterfeit drugs for weight loss is widespread owing to their easy and rapid availability. Since counterfeit weight-loss drugs are not prepared under the rigorous standard of Good Manufacturing Practice (GMP), they pose a risk to public health and cause significant side effects. To counteract the risk posed by counterfeit drugs, we investigated counterfeit weight-loss drugs seized by the Incheon Customs Services using UHPLC-PDA. Five of 23 confiscated samples with distinctive pink-coloured coating contained levothyroxine, sennoside A and B, and phenolphthalein in amounts ranging from 0.03-132.40 mg/g. In addition, three unknown compounds in one of the adulterated samples containing phenolphthalein were structurally elucidated by several analytical techniques. Their accurate masses corresponded to molecular formula of C₃₄H₂₂O₇, C₃₄H₂₀O₆, and C₂₀H₁₂O₃, respectively. These compounds were identified as impurities, possibly produced during the synthesis of phenolphthalein or by improper removal during purification. These impurities were detected for the first time in counterfeit drugs.