The thyroid gland is regulated by the pituitary gland by secreting thyroid stimulating hormone (TSH) to produce thyroxine (T3) and triiodothyronine (T4); when the levels of these are sufficient in the blood the pituitary gland detects the levels and then reduces the secretion of TSH and therefore the levels of T3 and T4 are maintained within normal limits, playing a very important role in the organism because they regulate growth and development, cardiac activity and blood pressure and the way in which the body uses and stores energy (Bhakat et al., 2023; Durá-Travé & Gallinas-Victoriano, 2024). One of the most common disorders is hyperthyroidism or thyrotoxicosis, which results from an excess in the synthesis of thyroid hormone (Alexander et al., 2017). The prevalence of this pathology in the general population is 0.5%, and it occurs more frequently in women than in men. It has been observed that in women it appears between the third and fourth decade, while in men the highest incidence occurs in the last decades of life (Korevaar, 2017). These patients may present insomnia, irritability, psychomotor agitation, affective lability, memory impairment and sometimes psychotic symptoms (Stagnaro-Green, 2017).

At present there are a large number of toxic substances to which we are exposed through environmental pollution, which occurs globally. These substances are toxic not only to humans but also to ecosystems and are used indiscriminately mainly for economic reasons (Tang et al., 2021). Among these toxic agents are lead and mercury, which are heavy metals with well-known toxic effects, these effects occur due to exposure to these elements or to compounds containing them. However, studies on the effect of Pb and Hg on thyroid function and particularly on TSH and T3 free levels are scarce (Desai et al., 2022).

Based on the problems described above, and that currently specialists in cadiologia and endocrinology have requested the determination of these metals in this type of patients the present study aimed to relationship the concentration of thyroid stimulating hormone (TSH), free thyroxine (T3F) and free triiodothyronine (T4F) with the levels of lead (Pb) and mercury (Hg) in patients (adults) with possible hyperthyroidism.