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Synthroid

Name: Synthroid
Brand: Mylan
Availability: InStock

Levothyroxine

Prescription required

$67.00

25mcg · 90 tablets · 3 months supply

BrandBranded medicine· By Mylan

$22.33 per month

Strength

How long a supply?

3 months$22.33 a monthOne-off$67.00

6 months$22.33 a monthOne-off$134.00

Supplied from Canada

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Annual cost

$268a year at this pack size

Prescription required

Upload your prescription after ordering, or send it to our pharmacy team. We dispense only against a valid prescription.

25mcg

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FDA boxed warningNot for treatment of obesity or for weight loss

Thyroid hormones, including SYNTHROID, either alone or with other therapeutic agents, should not be used for the treatment of obesity or for weight loss.

In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction.

Larger doses may produce serious or even life threatening manifestations of toxicity, particularly when given in association with sympathomimetic amines such as those used for their anorectic effects.

Thyroid hormones, including SYNTHROID should not be used for the treatment of obesity or for weight loss.

Doses beyond the range of daily hormonal requirements may produce serious or even life threatening manifestations of toxicity.

Read this with the rest of the clinical information

About Synthroid

Overview

Synthroid tablets contain levothyroxine sodium, a synthetic form of the thyroid hormone T4 that is chemically identical to the hormone made by the human thyroid gland. It is used to replace thyroid hormone in people with hypothyroidism, whether present from birth or developed later. It is also used alongside surgery and radioiodine therapy to suppress thyroid-stimulating hormone (TSH) in certain well-differentiated thyroid cancers that depend on TSH. It works by supplying T4, which the body converts to T3, the hormone responsible for most thyroid hormone activity in cells.

What it treats

- Hypothyroidism (underactive thyroid), whether present from birth or acquired, caused by thyroid, pituitary or hypothalamic disorders. - TSH-dependent, well-differentiated thyroid cancer, to suppress thyroid-stimulating hormone (TSH) alongside surgery and radioiodine therapy.

Safety information

Side effects

Side effects of Synthroid mainly reflect excess thyroid hormone from overtreatment. These include headache, nervousness, anxiety, irritability, mood changes, trouble sleeping, shaking, muscle weakness or cramps, tiredness, increased appetite, weight loss, sweating, heat intolerance and fever. Diarrhea, vomiting, abdominal cramps, hair loss, flushing, rash and menstrual changes can also occur. Contact a doctor promptly if you develop a racing or irregular heartbeat, palpitations or shortness of breath. Seek urgent medical help for chest pain, seizures, or signs of a serious allergic reaction such as swelling or wheezing. Serious heart effects include angina, heart failure, heart attack and cardiac arrest. Older adults and people with heart disease are at increased risk of heart complications from overtreatment. Seizures have rarely been reported when levothyroxine treatment is started. Other important risks include reduced bone density, particularly in postmenopausal women, impaired fertility and raised liver test results. Blood sugar control may worsen in people with diabetes. Starting Synthroid before adrenal insufficiency has been treated can trigger an acute adrenal crisis. In children, increased pressure around the brain and slipping of the hip’s growth plate have been reported. Overtreatment can cause skull bones to fuse too early in infants or growth plates to close prematurely in children, reducing adult height. Allergic reactions to inactive ingredients can cause hives, itching, rash, swelling, wheezing, digestive symptoms, fever and joint pain. Allergy to levothyroxine itself is not known to occur.

FDA boxed warning

Not for treatment of obesity or for weight loss

Thyroid hormones, including SYNTHROID, either alone or with other therapeutic agents, should not be used for the treatment of obesity or for weight loss.

In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction.

Thyroid hormones, including SYNTHROID should not be used for the treatment of obesity or for weight loss.

Doses beyond the range of daily hormonal requirements may produce serious or even life threatening manifestations of toxicity.

A boxed warning is the strongest warning the US Food and Drug Administration requires on a medicine label. Text is taken from the official label, with internal section references removed.

When to call your doctor

- Seek immediate medical attention for chest pain or a fast or irregular heartbeat. - Get urgent help for shortness of breath, wheezing, or swelling of the face, lips or tongue. - Seek immediate medical attention for a seizure.

If symptoms are severe or getting worse quickly, seek emergency care rather than waiting.

Before taking this medicine

Do not take Synthroid if you have adrenal insufficiency (your adrenal glands do not make enough hormones) that has not been treated. Glucocorticoid replacement treatment must begin before Synthroid to avoid an acute adrenal crisis. Synthroid tablets should not be used to treat myxedema coma, a life-threatening thyroid emergency. Extra care and monitoring are needed in older adults and people with heart or blood vessel disease. Too much thyroid hormone can cause chest pain or abnormal heart rhythms, including atrial fibrillation. If you have diabetes, Synthroid may worsen blood sugar control. Blood sugar should be monitored when treatment is started, changed or stopped, and diabetes medicines may need adjustment. Excess thyroid hormone can reduce bone density, particularly after menopause. Careful monitoring is needed to avoid too much or too little thyroid hormone. Pregnancy may change treatment requirements. Certain foods and medicines can also affect treatment or the interpretation of thyroid blood tests.

Interactions

Several medicines and supplements can affect how Synthroid works or alter thyroid blood test results. Important interactions to discuss with your doctor include: Calcium carbonate and ferrous sulfate (iron) supplements can reduce levothyroxine absorption. The same applies to orlistat, bile acid sequestrants such as cholestyramine and colesevelam, ion exchange resins such as sevelamer and Kayexalate, sucralfate, proton pump inhibitors, and antacids containing aluminum or magnesium hydroxides or simethicone. Your doctor may recommend separating administration times or monitoring thyroid function. Estrogen-containing contraceptives, oral estrogens, androgens, anabolic steroids, glucocorticoids, tamoxifen and some other medicines can change how thyroid hormones bind to proteins in the blood. Carbamazepine, phenytoin, salicylates, heparin and certain anti-inflammatory medicines can also affect thyroid hormone measurements. Phenobarbital and rifampin can increase levothyroxine breakdown. Amiodarone, propranolol and glucocorticoids can reduce conversion of thyroid hormone T4 to T3. Synthroid may worsen blood sugar control in people taking diabetes medicines or insulin. Blood sugar needs careful monitoring when thyroid treatment is started, changed or stopped. Synthroid can also increase the effects of oral anticoagulants, requiring close blood-clotting tests, and may reduce the effects of digitalis heart medicines. Tricyclic or tetracyclic antidepressants, such as amitriptyline or maprotiline, may have stronger effects and increased toxicity when taken with Synthroid, including irregular heart rhythms and nervous system stimulation. Sertraline may change Synthroid treatment requirements. Ketamine with Synthroid may cause a marked rise in blood pressure and a rapid heartbeat. Sympathomimetic medicines may have increased effects and can increase the risk of inadequate blood flow to the heart in people with coronary artery disease. Tyrosine-kinase inhibitors, such as imatinib, may cause low thyroid hormone levels and require closer thyroid monitoring. Your prescriber may need to adjust treatment based on these interactions and test results.

Using Synthroid

Dosing

Dosing is set by your prescriber. Each health care professional may prescribe medication differently according to a patient's medical history and condition, so follow the directions on your prescription label and speak to your doctor or pharmacist before changing anything.

Storage

Store below 25°C in a dry place, in the original pack, away from direct light and moisture. Do not keep it in a bathroom. Keep all medicines out of the sight and reach of children.

Clinical information on this page is summarised from the US FDA label SYNTHROID (LEVOTHYROXINE SODIUM) TABLET [APHENA PHARMA SOLUTIONS - TENNESSEE, LLC] (DailyMed, retrieved 19 September 2026).

Patient information and references

Official and supporting information to read alongside advice from your prescriber or pharmacist.

Prescribing information (professional PDF)

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