Poisoning with Thyroid Hormones Used Illegally—Systematic Review

<b>Background/Objectives</b>: Thyroid hormones, considered safe in therapeutic doses, are used to treat hypothyroidism, a common condition. Due to a combination of factors, including their mechanism of action, availability, and low price, these drugs are used illegally, mainly to improve performance, to assist in weight loss, or for attempting suicide. Their overuse can lead to serious health consequences, including death. Although thyroid hormones are abused, there are no studies assessing the scale, characteristics, and consequences of their illegal use. The aim of this study was to evaluate case reports of thyroid hormone poisoning from the last 30 years, assessing their dynamics and characteristics. <b>Methods</b>: Full-text clinical case studies were obtained by searching PubMed, Google Scholar, MEDLINE, Embase, Web of Science, and Scopus for the following terms: "thyroid hormones", "thyroxine", "levothyroxine", "triiodothyronine", and "liothyronine", as well as "intoxication", "overdose", and "poisoning". This study adhered to Preferred Reporting for Systematic Reviews and Meta-analyses (PRISMA) guidelines for systematic reviews. <b>Results</b>: Thyroid hormones are abused particularly by athletes, persons trying to lose weight, or those attempting suicide. There has been an upward trend in thyroid hormone poisoning over the past 30 years, particularly since 2015. The same trend has been observed in cases of thyroid hormone use for doping, among other performance-enhancing drugs. Thyroid hormone use for doping was the most common cause of poisoning with these drugs, with other clinical manifestations from poisonings due to other causes. No upward trend has been observed in the use of thyroid hormones in suicide attempts since 2017, as this number remains stable. <b>Conclusions</b>: Although exploratory in nature, our work indicates that thyroid hormone poisoning, associated mostly with the illegal use of anabolic-androgenic steroids, exhibits an increasing tendency. Moreover, thyroid hormone abuse is an important issue in suicidology.