What is the most common cause of hyperthyroidism?

Grave's disease is the most common cause of hyperthyroidism, representing a significant portion of cases diagnosed in clinical practice. This autoimmune disorder leads to the overstimulation of the thyroid gland due to the presence of antibodies that activate the thyrotropin receptor. The resultant increase in thyroid hormone production contributes to the clinical manifestations of hyperthyroidism, such as weight loss, heat intolerance, and palpitations.

It is important to understand the context of other conditions listed. Thyroiditis, including subacute and autoimmune types, can cause temporary hyperthyroidism but is not as prevalent as Grave's disease. Hashimoto's disease, primarily known for causing hypothyroidism, can lead to transient hyperthyroid phases but is generally associated with a gradual loss of thyroid function. A pituitary adenoma may cause hyperthyroidism through excess secretion of thyroid-stimulating hormone (TSH), but this scenario is much less common compared to the direct stimulation by antibodies in Grave's disease. Thus, the prevalence and mechanism of action make Grave's disease the leading cause of hyperthyroidism.