What Causes Fatigue and Drowsiness in Hyperthyroidism?

Patients with hyperthyroidism may experience fatigue and excessive daytime sleepiness due to: 1) psychological factors; or 2) hypothyroidism. Details are as follows:

1) Psychological factors: Hyperthyroidism typically presents with hypermetabolic symptoms, such as heightened mental alertness and irritability. Prolonged mental overstimulation—especially when accompanied by insomnia at night—may lead to daytime fatigue and drowsiness. In such cases, standardized drug therapy is essential to alleviate hyperthyroid symptoms and prevent fatigue and sleepiness resulting from chronic insomnia.

2) If thyroid function tests reveal coexisting hypothyroidism, this suggests that the hyperthyroidism has been controlled, but lifelong thyroid hormone replacement therapy (e.g., levothyroxine) will be required to manage the newly developed hypothyroidism.

Patients with hyperthyroidism should maintain a relaxed and calm mindset, ensure adequate rest, limit intake of iodine-rich foods (e.g., kelp, seafood), strictly adhere to their physician’s instructions regarding medication timing and dosage, and promptly return for follow-up evaluation if any discomfort arises—so that the underlying cause can be identified and appropriately managed.