Once the dose of levothyroxine is adjusted, insomnia should not be a side effect.

Most people who take this medicine or similar ones have an under active thyroid. This is called hypothyroidism.

Doctors use the result of a blood test, called TSH (for thyroid stimulating hormone) to guide proper dosing.

TSH is made by the pituitary gland in the brain and released into the blood stream. The pituitary gland releases more or less TSH depending on the blood level of thyroid hormone.

If you are not taking an adequate dose of levothyroxine, the pituitary gland will release more TSH into the blood. The opposite happens when the thyroid level is too high; the pituitary turns off the release of TSH.

If you are having insomnia and think it may be related to your levothyroxine, you and your doctor may decide to lower your dose. This might be true even if your TSH goes up a little higher than normal. How you feel is just as important as your TSH level.