Several large cohort studies have shown an association between exogenous thyrotoxicosis and cognitive impairment or dementia.1,2 In contrast, a recent multicohort individual participant data analysis of more than 74 000 adults did not demonstrate consistent associations between thyroid dysfunction and scores on tests of executive function, memory, or risk of dementia.3 However, while not statistically significant, individuals with overt hyperthyroidism in this study had about a 50% increased risk of dementia compared with those with normal thyroid function.