Final answer:
An anti-thyroid drug can cause a euthyroid state by regulating thyroid hormone levels and restoring normal thyroid function.
Step-by-step explanation:
An anti-thyroid drug can cause a euthyroid state when it effectively controls the production of thyroid hormones and brings the levels back to normal. These drugs work by inhibiting key enzymes and processes involved in thyroid hormone production, such as iodine uptake or thyroperoxidase activity. By regulating the thyroid hormone levels, these drugs can help restore a euthyroid state, which means the thyroid functions normally.