Synthroid Oral Precautions and Side Effects

  • Precautions

    Before taking levothyroxine, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

    Before using this medication, tell your doctor or pharmacist your medical history, especially of:

    • increased thyroid hormones (thyrotoxicosis)
    • decreased adrenal gland function
    • heart disease (such as coronary artery disease, irregular heartbeat)
    • high blood pressure
    • diabetes

    Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).

    Current information shows that this drug may be used during pregnancy. Tell your doctor if you are pregnant because your dose may need to be adjusted.

    Levothyroxine passes into breast milk but is unlikely to harm a nursing infant. Consult your doctor before breast-feeding.

    Side Effects

    Hair loss may occur during the first few months of treatment. This effect is usually temporary as your body adjusts to this medication. If this effect persists or worsens, tell your doctor or pharmacist promptly.

    Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

    Tell your doctor immediately if any of these unlikely but serious effects of high thyroid hormone levels occur:

    • increased sweating
    • sensitivity to heat
    • mental/mood changes (such as nervousness, mood swings)
    • tiredness
    • diarrhea
    • shaking (tremor)
    • headache
    • shortness of breath

    Get medical help right away if any of these rare but serious effects of high thyroid hormone levels occur:

    • chest pain
    • fast/pounding/irregular heartbeat
    • swelling hands/ankles/feet
    • seizures

    A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including:

    • rash
    • itching/swelling (especially of the face/tongue/throat)
    • severe dizziness
    • trouble breathing

    This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

    In the US -

    Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

    In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

    Warning

    This medication should not be used for weight loss. Normal doses of this medication will not work for weight loss, and large doses of this medication may cause serious, possibly fatal side effects, especially when taken with diet pills.