Levothyroxine is a thyroid hormone supplement used to treat people who do not produce enough thyroid hormone on their own. Levothyroxine helps to reduce the symptoms of low thyroid hormone such as weight gain, sensitivity to cold, lack of energy, and dry skin. It may take several weeks for this medication to have a noticeable effect on your condition.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. As well, some forms of this medication may not be used for all of the conditions discussed here. If you have not discussed this with your doctor or are not sure why you are being given this medication, speak to your doctor. Do not stop using this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to use this medication if their doctor has not prescribed it.

The dose of levothyroxine depends on how much of the hormone is needed to bring blood levels back to the normal range. This is determined by blood tests that are done in a laboratory. The starting dose will depend on the general physical condition of the person taking the medication and the severity and duration of time that symptoms of low thyroid hormone levels have been present.

You should take this medication once a day at the same time every day to ensure a consistent effect.

Signs that you may be getting too much thyroid hormone may include chest pain, increased heart rate, palpitations, excessive sweating, heat intolerance, and nervousness. If you think your dose of thyroid hormone may be too high, consult your doctor as soon as possible.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones given here, do not change the way that you are using the medication without consulting your doctor.

It is important to use this medication exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from light and moisture, and keep it out of the reach of children.

This medication is available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms listed here. The forms available for the specific brand you have searched are listed under "What form(s) does this medication come in?"

Do not dispose of medications in wastewater (e.g. down the sink or in the toilet) or in household garbage. Ask your pharmacist how to dispose of medications that are no longer needed or have expired.

25 µg
Each orange, round, colour-coded, scored tablet, debossed with "SYNTHROID" on one side and potency on the other side contains levothyroxine sodium, USP 25 µg. Nonmedicinal ingredients: acacia, confectioner's sugar, FD&C Yellow No. 6, lactose, magnesium stearate, povidone, and talc.

50 µg
Each white, round, colour-coded, scored tablet, debossed with "SYNTHROID" on one side and potency on the other side contains levothyroxine sodium, USP 50 µg. Nonmedicinal ingredients: acacia, confectioner's sugar, lactose, magnesium stearate, povidone, and talc.

75 µg
Each violet, round, colour-coded, scored tablet, debossed with "SYNTHROID" on one side and potency on the other side contains levothyroxine sodium, USP 75 µg. Nonmedicinal ingredients: acacia, confectioner's sugar, FD&C Blue No. 2, FD&C Red No. 40, lactose, magnesium stearate, povidone, and talc.

88 µg
Each olive, round, colour-coded, scored tablet, debossed with "SYNTHROID" on one side and potency on the other side contains levothyroxine sodium, USP 88 µg. Nonmedicinal ingredients: acacia, confectioner's sugar, D&C Yellow No. 10, FD&C Blue No. 1, FD&C Yellow No. 6, lactose, magnesium stearate, povidone, and talc.

100 µg
Each yellow, round, colour-coded, scored tablet, debossed with "SYNTHROID" on one side and potency on the other side contains levothyroxine sodium, USP 100 µg. Nonmedicinal ingredients: acacia, confectioner's sugar, D&C Yellow No. 10, FD&C Yellow No. 6, lactose, magnesium stearate, povidone, and talc.

112 µg
Each rose, round, colour-coded, scored tablet, debossed with "SYNTHROID" on one side and potency on the other side contains levothyroxine sodium, USP 112 µg. Nonmedicinal ingredients: acacia, confectioner's sugar, D&C Red No. 27, D&C Red No. 30, lactose, magnesium stearate, povidone, and talc.

125 µg
Each brown, round, colour-coded, scored tablet, debossed with "SYNTHROID" on one side and potency on the other side contains levothyroxine sodium, USP 125 µg. Nonmedicinal ingredients: acacia, confectioner's sugar, FD&C Blue No. 1, FD&C Red No. 40, FD&C Yellow No. 6, lactose, magnesium stearate, povidone, and talc.

137 µg
Each turquoise, round, colour-coded, scored tablet, debossed with "SYNTHROID" on one side and potency on the other side contains levothyroxine sodium, USP 137 µg. Nonmedicinal ingredients: acacia, confectioner's sugar, FD&C Blue No. 1, lactose, magnesium stearate, povidone, and talc.

150 µg
Each blue, round, colour-coded, scored tablet, debossed with "SYNTHROID" on one side and potency on the other side contains levothyroxine sodium, USP 150 µg. Nonmedicinal ingredients: acacia, confectioner's sugar, FD&C Blue No. 2, lactose, magnesium stearate, povidone, and talc.

175 µg
Each lilac, round, colour-coded, scored tablet, debossed with "SYNTHROID" on one side and potency on the other side contains levothyroxine sodium, USP 175 µg. Nonmedicinal ingredients: acacia, confectioner's sugar, D&C Red No. 27 & D&C Red No. 30, FD&C Blue No. 1, lactose, magnesium stearate, povidone, and talc.

200 µg
Each pink, round, colour-coded, scored tablet, debossed with "SYNTHROID" on one side and potency on the other side contains levothyroxine sodium, USP 200 µg. Nonmedicinal ingredients: acacia, confectioner's sugar, FD&C Red No. 40, lactose, magnesium stearate, povidone, and talc.

300 µg
Each green, round, colour-coded, scored tablet, debossed with "SYNTHROID" on one side and potency on the other side contains levothyroxine sodium, USP 300 µg. Nonmedicinal ingredients: acacia, confectioner's sugar, D&C Yellow No. 10, FD&C Blue No. 1, FD&C Yellow No. 6, lactose, magnesium stearate, povidone, and talc.

Levothyroxine should not be used by anyone who:

• is allergic to levothyroxine or to any of the ingredients of the medication
• is having a heart attack
• has acute thyrotoxicosis (too much thyroid hormone in their system)
• has uncorrected adrenal insufficiency

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent. The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• diarrhea
• fever
• hair loss (temporary; particularly in children during the first month of treatment)
• headache
• increased appetite
• menstrual cycle changes
• nervousness or irritability
• sensitivity to heat
• stomach cramps or upset stomach
• tremor (shaking)
• weight loss

Although most of these side effects listed below don't happen very often, they could lead to serious problems if you do not check with your doctor or seek medical attention.

Stop taking the medication and seek immediate medical attention if any of the following occur:

• chest pain, irregular heartbeat, or shortness of breath
• severe allergic reaction (e.g., hives; difficulty breathing; wheezing; or swelling of the eyes, mouth, or lips)
• vomiting

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Bone density: Levothyroxine can cause bones to lose thickness. People at an increased risk for osteoporosis (bone thinning) or who are taking medications that reduce bone thickness (e.g., prednisone or antiseizure medications) should discuss this with their doctor before starting treatment. Your doctor may monitor your bone thickness while you are taking this medication.

Diabetes: Levothyroxine raises blood sugar levels. For people with diabetes, this may result in an increase in the requirements for insulin or antidiabetes medications. Monitor your blood sugar more closely when starting or changing doses of this medication.

Heart disease: When starting levothyroxine, people with heart disease may be started on a lower dosage as it may cause the heart to work harder than it has been used to.

Signs of getting too much or too little medication: Contact your doctor as soon as possible if you notice any signs of getting too much medication (such as chest pain, confusion, fast or irregular heartbeat, mood swings, muscle weakness, psychosis, extreme restlessness, yellow eyes or skin, or shortness of breath) or signs of not getting enough medication (such as clumsiness, coldness, constipation, dry, puffy skin, listlessness, muscle aches, sleepiness, tiredness, weakness, or weight gain).

Weight loss: Levothyroxine should not be used for weight loss. Larger doses could cause serious side effects especially when taken together with other medications for weight loss.

Breast-feeding: The use of appropriate amounts of this medication by breast-feeding women has not been shown to cause harm for breast-fed babies.

Pregnancy: When this medication is used to regulate the levels of thyroid hormone, treatment is considered necessary for pregnant women.

Seniors: Seniors may be more sensitive to the effects of levothyroxine.

There may be an interaction between levothyroxine and any of the following:

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications that you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.