Key takeaways

Synthroid (levothyroxine sodium) is an FDA-approved medication that replaces thyroid hormone, primarily used to treat hypothyroidism, and helps regulate the body’s energy and metabolism.
Synthroid requires careful dosage management, with adjustments potentially needed over time due to changes in thyroid hormone levels, and it should be taken on an empty stomach with water before breakfast for optimal effectiveness.
While Synthroid can regulate thyroid hormone levels and metabolism, it is not intended for weight loss. Synthroid alternatives include other T4 formulations, T3 medications, and natural desiccated thyroid (NDT) treatments, depending on individual needs and responses.

If you feel tired around the clock, have consistently dry skin, or notice that your face is slightly puffy, you could have hypothyroidism, a condition where your thyroid gland doesn’t produce enough thyroid hormone. A Synthroid prescription can help.

Synthroid is an FDA-approved thyroid medicine that commonly treats hypothyroidism and regulates thyroid hormone levels.

What is Synthroid?

Synthroid (levothyroxine sodium) is a type of thyroid medicine that replaces the hormone naturally produced by the thyroid gland and helps regulate the body’s energy and metabolism. AbbVie manufactures this hormone medication. It mainly treats hypothyroidism, though it can also treat an enlarged thyroid gland or thyroid cancer in some cases.

When the thyroid malfunctions, the body doesn’t have enough thyroxine—the primary hormone produced and released by the thyroid gland. Thyroxine plays a vital role in digestion, brain development, and heart and muscle function. The main ingredient in Synthroid, levothyroxine sodium, works in the same way as thyroxine (also known as T4), allowing the body to function normally.

Levothyroxine sodium is a synthetic form of thyroxine. It’s the active ingredient in Synthroid, the brand-name version of levothyroxine. Inactive ingredients in Synthroid improve absorption, preserve the drug, and add color.

Synthroid is a prescription drug and can not be bought over the counter. Talk to your healthcare provider to determine if the drug is right for you.

What is Synthroid used for?

Synthroid is used to treat hypothyroidism, a condition where the body produces a low amount of thyroid hormone. It can also treat and prevent goiters caused by hypothyroidism. A goiter is an enlarged thyroid gland that can occur due to hormone imbalances, iodine deficiency, thyroid surgery, or other underlying conditions.

Do not use Synthroid to treat non-cancerous growths, temporary cases of hypothyroidism, or thyroid enlargement in patients who have normal iodine levels.

Synthroid dosages

Brand-name Synthroid is available as a tablet in 12 different strengths. Talk to your healthcare provider about which dosing option is best for you. The starting dose may differ as time goes on since thyroid hormone levels will likely change over time.

Synthroid pill identifier
Color of tablet	Strength
Orange	25 mcg
White	50 mcg
Violet	75 mcg
Olive	88 mcg
Yellow	100 mcg
Rose	112 mcg
Brown	125 mcg
Turquoise	137 mcg
Blue	150 mcg
Lilac	175 mcg
Pink	200 mcg
Green	300 mcg

Generic versions of Synthroid come in capsules, oral solutions, and powders for injections. Capsules range from 13 to 150 mcg, oral solution ranges from 12 to 200 mcg/mL, and powder is available in 100, 200, and 500 mcg per vial.

These are the available strengths and forms of Synthroid for adults. If you’re a senior citizen, or have a child who needs to take Synthroid, talk to your healthcare provider about the best dosage. Before starting the medication, your physician will test your TSH (thyroid-stimulating hormone) levels to determine the right dosage.

When should Synthroid be taken?

For Synthroid to be effective, it should be taken at the same time every day, following these steps:

Take Synthroid once a day before breakfast.
Make sure you take Synthroid with only water and on an empty stomach.
Wait 30 minutes to an hour before eating or drinking.

Synthroid restrictions

There are no restrictions on who can use Synthroid—adults, children, and the elderly can all take the drug. Children can take the medicine if the tablet is crushed and mixed with one to two teaspoons of water.

Synthroid interactions

Before you start taking Synthroid, talk to your healthcare provider about your medical history, including medical conditions and any medicine that you’re currently taking. If you’re taking other medications while taking Synthroid, your dosage for Synthroid or the other medications may need to change.

Synthroid may have interactions with the following drugs:

Antacids, such as Maalox, Mylanta, or Pepcid Complete
Anticonvulsants
Beta blockers
Birth control pills
Calcium carbonates, such as Tums and Alka-Mints
Cholestyramine
Colestipol
Corticosteroids
Iron supplements
Magnesium supplements
Simethicone
Stomach acid reducers, such as Prilosec, Prevacid, and Zegerid
Sucralfate
Tamoxifen
Tricyclic antidepressants

If you’re taking any of these drugs, speak to your healthcare provider, as they may want you to stop taking one of these medications or change the way you take your medications. This is not a complete list of Synthroid interactions. Share all supplements and prescriptions you take with your doctor or pharmacist.

Tell your healthcare provider if you:

Take weight-loss drugs
Have uncorrected adrenal problems
Take iron, calcium supplements, or antacids
Are pregnant or breastfeeding
Have heart disease or diabetes
Experience blood clotting or have a pituitary gland condition
Have low bone mineral density levels

Additionally, some foods can interfere with the effectiveness of Synthroid. Some of these items include:

Foods containing soy, soybean flour, or cottonseed meal
Infant formula containing soybeans
Walnuts
Grapefruit juice
Dietary fibers

What to expect when using Synthroid

Some people may feel better within a few days of starting Synthroid, but it may take months before your hormone levels get back to normal. Typically, Synthroid will begin improving symptoms within two weeks of starting the drug. Around the six-week mark is when a healthcare provider will test TSH levels again, monitor thyroid function, and make small adjustments to your dosage to ensure that your thyroid hormone levels are correct.

The effectiveness of Synthroid may be changed based on changes in the amount of thyroid hormone your body produces, so your healthcare provider will have to adjust dosage requirements. Major life events, like pregnancy, menopause, or aging can impact your thyroid hormone levels. Even if your thyroid symptoms go away, don’t stop taking Synthroid or change the way you take it without first talking to a doctor.

Note: If you take thyroid replacement drugs, you may have to take them for life.

What are the side effects of Synthroid?

“The major side effects include headache or itching,” according to thyroid specialist Brittany Henderson, MD, ECNU, lead author of What You Must Know About Hashimoto’s Disease. “Some patients are sensitive to the dyes and fillers in the medicine. If one experiences these symptoms, it may be best to switch to another thyroid medication.”

Here are some other side effects caused by Synthroid:

Partial hair loss
Sweating
Hot flashes
Heat intolerance
Irritability
Nausea
Sleeplessness
Changes in appetite or weight

More severe side effects include irregular heartbeat, heart palpitations, abnormal heart rate, heart failure, high blood pressure, chest pain, tremors, shortness of breath or difficulty breathing, leg cramps, vomiting, diarrhea, fever, changes in menstrual periods, hives, skin rash, or an allergic reaction. If you experience one or more of these symptoms, seek medical advice right away.

The list above is not a complete list of side effects. Talk to your healthcare provider about other possible side effects, drug interactions, and related drug information.

Long-term, Synthroid should normalize your thyroid hormone levels and regulate your metabolism.

Can Synthroid help you lose weight?

Though Synthroid will normalize your thyroid hormone production and your metabolism, it’s not a weight-loss drug. Your weight should stabilize while on the medication, and you shouldn’t be gaining or losing excessive amounts of weight.

Are there alternatives to Synthroid?

According to thyroid specialist Dr. Henderson, there are multiple thyroid formulations.

“T4-only formulations include Synthroid; levothyroxine (the generic for Synthroid); Levoxyl; Unithroid; Tirosint; and Tirosint-SOL (the solution form of T4). Cytomel (or liothyronine) are forms of T3 (or active thyroid hormone), and are additional medicines sometimes added to T4,” says Dr. Henderson.

“Natural desiccated thyroid (or NDT) is also an option. NDT is pig thyroid in pill form and includes both T4 and T3. Options include NP Thyroid; Armour; Nature-Throid; and WP Thyroid. Additionally, patients can get T4 and T3 medicines through a compounding pharmacy in different strengths and formulations.”

Here’s a general overview of each Synthroid alternative:

Levoxyl can be used to treat hypothyroidism, enlarged thyroid glands, and thyroid cancer. It replaces the hormone usually produced by your thyroid gland that regulates metabolism and energy.
Unithroid is another thyroid drug that can be used in place of Synthroid to regulate your thyroid hormone levels.
Tirosint is the only thyroid medication that comes in a gel capsule. It may be best for people with hypothyroidism who have food or ingredient sensitivities, as Tirosint doesn’t have sugars, dyes, alcohol, gluten, lactose, or any other excipients used to make the tablets.
Tirosint-SOL is an oral solution that contains only three ingredients: levothyroxine, glycerol, and water. Unlike other tablets or capsules, Tirosint-SOL is a liquid that comes in a dropper. It doesn’t contain alcohol and is approved for patients of all ages.
Cytomel, Also known as liothyronine sodium, Cytomel can be used to treat severe hypothyroidism. It contains liothyronine, a synthetic form of natural thyroid hormone.
Natural desiccated thyroid (NDT) is made from the thyroid glands of pigs. NDT contains all four thyroid hormones that our body needs: T1, T2, T3, and T4. It may be a natural alternative for people who still have hypothyroidism symptoms or low T3 levels while taking other thyroid medications.

Work with your healthcare provider to determine which is right for you.