Hyperthyroidism is a common hormonal condition diagnosed in cats. It occurs when benign nodules or growths form in the thyroid gland, leading to an overproduction of metabolism-controlling hormones. It is unclear what causes these nodules to grow in the first place (certain chemicals have been investigated but nothing has been proven). However, they are usually benign and don’t spread elsewhere in the body (not metastatic). The risk factors that make some cats more likely to develop the condition than others include advancing age, being a non-pedigree breed and being female.