Low TSH levels typically indicate that the thyroid gland is producing an excessive amount of thyroid hormones. This condition is known as hyperthyroidism, or an overactive thyroid. A range of conditions can lead to hyperthyroidism and consequently, low TSH levels. These primarily include:

* Graves' disease
* Toxic multinodular goiter or solitary toxic adenoma (nodular thyroid)
* Thyroiditis (inflammation of the thyroid gland), which can cause a temporary release of stored hormones
* Excessive intake of iodine, such as from certain medications, supplements, or high consumption of iodized salt
* Overuse of thyroid hormone medication (e.g., levothyroxine) or natural supplements containing thyroid hormones
* Transient hyperthyroidism during early pregnancy (gestational thyrotoxicosis)