What Is Levothyroxine for? Plus 9 Things You May Not Know About Taking It

Levothyroxine (Synthroid) is the first-choice medication for low thyroid hormone levels (hypothyroidism). It’s one of the most commonly prescribed medications in the U.S. And even though it’s been around since 1949, levothyroxine might still be new to you.

Here, we’ll review what levothyroxine is used for and other facts that will get you up to speed and help you maximize the benefits of this medication.

1. What is levothyroxine used for?

Levothyroxine is an oral medication that treats low thyroid hormone levels. Thyroid hormone is necessary to help your body use energy. It keeps your brain, heart, and other organs functioning as they should. When your thyroid levels are lower than normal, you can gain weight, feel tired, and find it hard to tolerate cold temperatures. You may also feel constipated or even have feelings of depression.

Low thyroid hormone levels have several different causes, such as:

• Hashimoto’s thyroiditis (an autoimmune condition)

• Thyroid cancer treatment

• Overactive thyroid treatment

• Low iodine levels

• Riedel’s thyroiditis (a rare inflammatory condition)

Medications and other health conditions can also lead to low thyroid levels. But taking the right amount of levothyroxine can treat low thyroid levels regardless of what’s causing them.

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Levothyroxine comes in 12 different doses ranging from 25 mcg to 300 mcg. Your prescriber will monitor the thyroid hormone levels in your blood to determine the best levothyroxine dosage to keep them within the desired range.

2. You can take levothyroxine at night

You’ve probably heard that you should take levothyroxine in the morning at least 30 to 60 minutes before breakfast. That’s because it's absorbed better on an empty stomach.

But this may be tough if you have an unpredictable schedule in the morning. In this case, you can take levothyroxine every night at bedtime instead. Studies show that taking levothyroxine at bedtime is just as effective as taking it 1 hour before breakfast.

If you take levothyroxine at bedtime, just make sure it’s at least 4 hours after your last meal of the day or any other medications and supplements.

3. It’s a lab-made version of the T4 hormone

Levothyroxine is a lab-made (synthetic) version of T4 (thyroxine) — a natural thyroid hormone. It works the same way as the T4 made by your thyroid gland. The body turns T4 into T3 (triiodothyronine), which is the “active” form of thyroid hormone.

Armour Thyroid contains both T3 and T4 taken from the thyroid glands of pigs. Although it’s often referred to as a more “natural” thyroid medication, it doesn’t provide reliable, consistent results the way that levothyroxine does. So most medical experts prefer levothyroxine.

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• What’s the best way to take levothyroxine? Here are some pharmacist-backed tips to help you get the most from your thyroid hormone medication.

Liothyronine (Cytomel) is a thyroid medication that only contains T3. Your prescriber may have you take it along with levothyroxine if your thyroid hormone levels aren’t responding to levothyroxine alone.

4. Switching between brand and generic versions can be tricky

There are a number of brand-name levothyroxine tablets available, such as:

• Synthroid

• Euthyrox

• Levo-T

• Unithroid

• Levoxyl

• Tirosint

Levothyroxine is also available as a lower-cost generic.

Brand-name and generic forms of levothyroxine are equally effective at treating hypothyroidism. But unlike other medications, you shouldn’t switch between brand and generic forms of this medication unless your prescriber OKs it. Instead, you should stick with the same brand-name or generic product throughout your treatment whenever possible. This is because even slight differences between products could lead to unwanted changes in your thyroid hormone levels.

5. You might not notice levothyroxine’s effects right away

It may take 4 to 6 weeks to see the full effect of levothyroxine. It’s important to be patient and continue taking the medication as prescribed even if you don’t notice any changes at first. After this time has passed, your prescriber may check your thyroid levels and adjust your levothyroxine dosage if needed.

Keep in mind, it might take a few months and/or multiple dose adjustments to find the right levothyroxine dosage for you.

6. Levothyroxine has some side effects to be aware of

Levothyroxine is generally tolerated well. Most of levothyroxine side effects are related to the dose. If thyroid hormone levels go too high, you could experience any of the following symptoms:

• Not being able to tolerate heat

• Sweating excessively

• Fast heart rate or palpitations

• Diarrhea

• Unexpected weight loss

• Nervousness or anxiety

If you experience any of these side effects, talk to your prescriber. They can help adjust your dose as needed. More often than not, a dose adjustment takes care of these symptoms.

7. Levothyroxine interacts with some medications and foods

Levothyroxine can interact with different medications. Some medications, such as antacids, omeprazole (Prilosec), and phenobarbital, could lower levothyroxine levels, making it less effective. Others, such as amiodarone (Pacerone) and beta blockers, could increase levothyroxine levels, raising the risk of side effects.

Levothyroxine can also interact with certain supplements (such as iron, calcium, and vitamin C) and foods (such as coffee, grapefruit juice, and alcohol). They interfere with how well you absorb levothyroxine. That’s why it’s recommended to take it on an empty stomach, either in the morning 30 to 60 minutes before breakfast or at bedtime at least 4 hours after food or other medications.

If you’re taking a medication that interacts with levothyroxine, your prescriber can adjust your dosage to ensure your thyroid hormone levels stay within a safe range. Just be sure to stay consistent with how you take your medications. And let your prescriber know if you stop or start taking any new medications.

8. It’s safe to take during pregnancy

It’s safe to keep taking levothyroxine during pregnancy. In fact, keeping your thyroid hormone levels within the desired range is essential for both you and your growing fetus.

Some people may also develop hypothyroidism for the first time while pregnant. In this case, levothyroxine is the first-choice treatment option.

It’s common for your levothyroxine dosage to change during and after pregnancy. So you’ll likely need extra monitoring during this time. Be sure to follow your healthcare team’s instructions and reach out with any questions.

9. Liquid levothyroxine solutions are also available

Levothyroxine is available as an oral liquid under the brand names Tirosint-SOL and Thyquidity. These can be a good option for those who have trouble swallowing pills. Levothyroxine tablets may also contain gluten or lactose. So liquid options may be better for those with a severe gluten or lactose intolerance.

10. You shouldn’t stop taking levothyroxine on your own

Taking levothyroxine every day is key to maintaining healthy levels of thyroid hormone. A study found that people who took levothyroxine consistently had lower healthcare costs and were less likely to develop other illnesses than those who didn’t.

Missing too many doses or stopping levothyroxine altogether can leave your hypothyroidism untreated. This can lead to serious health problems over time. If you’re having trouble with side effects or if you have other concerns about taking levothyroxine, talk to your healthcare team. Don’t stop taking it on your own.

How to save on levothyroxine

There are many ways to save on levothyroxine, which is available as both a brand-name and generic medication.

• Save with GoodRx. GoodRx can help you save over 80% off the average retail price of the generic version. Generic levothyroxine at certain pharmacies is less than $4.00 with a free GoodRx discount.

• Save with a copay savings card. If you have commercial insurance and meet eligibility requirements, brand-name Synthroid is as little as $25 and brand-name Unithroid is as little as $3 using a savings card from the manufacturer.

• Save with patient assistance programs. If you’re uninsured or underinsured, you may be eligible for Synthroid’s patient assistance program, which offers the medication free of cost.

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Written by:

Hindu Rao, PharmD, APh, BCACP

Hindu Rao, PharmD, APh, BCACP is a clinical assistant professor of pharmacy practice at Chapman University School of Pharmacy and a clinical pharmacist at Providence Medical Foundation. She specializes in chronic disease management and has her board certification in ambulatory care.

Edited by:

Stacia Woodcock, PharmD

Stacia Woodcock, PharmD, is a pharmacy editor for GoodRx. She earned her Doctor of Pharmacy degree from the University of Kentucky and is licensed in New York and Massachusetts.

Reviewed by:

Christina Aungst, PharmD

Christina Aungst, PharmD, is a pharmacy editor for GoodRx. She began writing for GoodRx Health in 2019, transitioning from freelance writer to editor in 2021.

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