Medically reviewed by Jessica Swirble, PharmD
Last updated on March 26, 2025
Drug Information | Side Effects | Use & Dosage | Request an Online Prescription
Levothyroxine is a synthetic thyroid hormone used to treat hypothyroidism (underactive thyroid) and certain thyroid-related conditions. It works by replacing or supplementing the thyroid hormone that your body naturally produces.
Hypothyroidism: Levothyroxine is primarily used to treat hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormone. This medication helps regulate thyroid hormone levels in the body, alleviating symptoms such as fatigue, weight gain, cold intolerance, and sluggishness.
Thyroid nodules: In certain cases, levothyroxine may also be used to shrink thyroid nodules or prevent the growth of goiters (enlarged thyroid glands).
Thyroid cancer: In some instances, levothyroxine is prescribed as part of thyroid cancer treatment. It is usually prescribed with radioactive iodine therapy and surgery.
Levothyroxine is a synthetic form of thyroxine (T4), one of the thyroid hormones produced by the thyroid gland. It functions similarly to natural thyroid hormone and helps restore thyroid hormone levels in individuals with hypothyroidism or thyroid-related conditions. Levothyroxine supplementation improves metabolic function and overall well-being in affected individuals.
Note that levothyroxine therapy requires regular monitoring of thyroid function through blood tests to ensure optimal hormone levels are maintained.
Levothyroxine is usually taken orally, on an empty stomach, at least 30 minutes to 1 hour before breakfast or as directed by your healthcare provider. It is recommended that you take it at the same time each day to maintain stable hormone levels.
Consult your healthcare provider for specific instructions on how to take levothyroxine properly.
The effects of levothyroxine on symptoms of hypothyroidism, such as fatigue and cold intolerance, may be noticeable within a few weeks of starting treatment. However, it may take several weeks to months to achieve the desired thyroid hormone levels. It’s important to take levothyroxine consistently to maintain the best treatment outcomes.
While levothyroxine is primarily used to treat hypothyroidism and related conditions, it may also be prescribed for other purposes, including:
Discuss any alternative uses of levothyroxine with your healthcare provider.
Levothyroxine is available as an oral tablet in various strengths, including 25mcg, 50mcg, 75mcg, 88mcg, 100mcg, 112mcg, 125mcg, 137mcg, 150mcg, 175mcg, 200mcg, and 300mcg. It is also available in oral solution form for pediatric use.
Generic versions of levothyroxine are available under different brand names.
Levothyroxine is a prescription medication. You will need a valid prescription from a licensed healthcare provider to obtain this drug.
The use of levothyroxine has been shown to cause side effects in some patients.
Common mild side effects of levothyroxine use include:
More severe side effects include:
Seek medical attention immediately if you experience any severe symptoms while taking levothyroxine. If you experience mild side effects that become severe or do not go away after a few days, speak to a healthcare provider right away.
Tell your healthcare provider about any existing medical conditions, allergies, or other medications you are taking before starting treatment with levothyroxine. This includes prescription drugs, over-the-counter medications, and dietary supplements, as they may interact with this drug.
Tell your provider if you are taking these medications or supplements:
You should also mention medical conditions such as:
If you are pregnant, planning to become pregnant, or breastfeeding, consult your healthcare provider before using levothyroxine to assess potential risks and benefits.
Take levothyroxine on an empty stomach, at least 30 minutes to 1 hour before breakfast or as directed by your healthcare provider.
Avoid consuming soybeans, walnuts, or foods high in dietary fiber while taking levothyroxine. Your dosage may need to be adjusted if you consume a high-fiber diet.
Do not eat grapefruit or consume grapefruit juice while taking levothyroxine.
Your healthcare provider will provide specific instructions regarding the use of levothyroxine with food, beverages, and other medications. It's essential to follow their guidance to ensure the effectiveness of the treatment and minimize the risk of side effects.
The symptoms of a levothyroxine overdose include:
If you experience any of these symptoms, call the poison control helpline at 1-800-222-1222. If an individual has collapsed, is having seizures, or is unresponsive, call 9-1-1 immediately.
Levothyroxine is available in various forms:
The typical starting dose of levothyroxine can vary based on the specific thyroid condition being treated, the patient's age, weight, and other individual factors. It is crucial to adhere closely to your healthcare provider's instructions regarding dosage and administration.
For the treatment of hypothyroidism in adults, the typical starting doses may be:
For pediatric patients with congenital hypothyroidism, the typical starting dose may range from 10 to 15 mcg per kg of body weight per day, adjusted based on age and severity of the condition.
Your healthcare provider will evaluate your medical history, thyroid function tests, and other relevant factors to determine the most appropriate starting dose for you.
Levothyroxine should be taken exactly as prescribed by your healthcare provider. It is important not to exceed the recommended dose or make changes to your medication regimen without consulting your provider.
If you have any questions about your dosage, contact your healthcare provider. If you want to talk to a provider right away, book an online doctor appointment on Sesame to discuss your concerns.
If you miss a dose, take it as soon as you remember it. If it's almost time for another dose of levothyroxine, skip the missed dose and take your next dose as scheduled. Do not take a double dose of levothyroxine.
Do not discontinue or alter your levothyroxine dosage without consulting with your healthcare provider as it may lead to thyroid hormone imbalances and related symptoms.
Attend follow-up appointments as recommended by your healthcare provider for thyroid function monitoring and dosage adjustments if needed.
Follow your healthcare provider's instructions regarding dosing and other recommendations for taking levothyroxine.
Store levothyroxine as directed by your healthcare provider or pharmacist. Proper storage is essential to maintain the medication's effectiveness. Levothyroxine should be stored at room temperature, away from excessive heat, light, and moisture.
Keep the medication out of the reach of children and ensure that the container is tightly closed.