Synthroid (levothyroxine sodium) is the most prescribed brand-name thyroid hormone replacement medication in the United States. It is a synthetic form of the T4 hormone, identical to what the human thyroid gland naturally produces. This medication is rigorously standardized to ensure consistent potency and reliable performance in every dose, providing a trusted solution for managing hypothyroidism. Proper use, under medical supervision, can effectively restore hormonal balance, alleviate symptoms, and significantly improve a patient’s overall metabolic health and quality of life.

Features

• Contains the active pharmaceutical ingredient levothyroxine sodium, a synthetic form of thyroxine (T4).
• Available in a wide range of precisely calibrated tablet strengths (e.g., 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg, 175 mcg, 200 mcg, 300 mcg) to allow for fine-tuned dosage titration.
• Manufactured under strict FDA-approved quality control standards to ensure batch-to-batch consistency and accurate hormone delivery.
• Formulated for oral administration as a scored tablet, which may be split for dosage adjustments as directed by a physician.
• Includes color-coding and clear imprints on each tablet for easy strength identification, reducing the risk of dosing errors.

Benefits

• Effectively restores normal thyroid hormone levels, reversing the biochemical deficiency of hypothyroidism.
• Alleviates the debilitating symptoms associated with an underactive thyroid, such as chronic fatigue, unexplained weight gain, depression, and brain fog.
• Helps normalize metabolic rate, which can lead to healthy weight management and improved energy utilization.
• Reduces the risk of long-term complications from untreated hypothyroidism, including elevated cholesterol levels, cardiovascular disease, and neurological issues.
• Supports normal growth and development in pediatric patients with congenital or acquired hypothyroidism.
• Provides a predictable and stable therapeutic effect due to its long half-life, allowing for once-daily dosing.

Common use

Synthroid is primarily indicated as hormone replacement therapy for the treatment of hypothyroidism, a condition characterized by an inadequate production of thyroid hormones by the thyroid gland. It is a lifelong therapy for most patients with this condition. It is also used as supplemental or suppressive therapy in the management of other thyroid disorders, including euthyroid goiters, subacute or chronic lymphocytic thyroiditis (Hashimoto’s disease), and as an adjunct to surgery and radioiodine therapy in the management of thyrotropin-dependent well-differentiated thyroid cancer.

Dosage and direction

The dosage of Synthroid is highly individualized and must be determined by a healthcare professional based on the patient’s age, body weight, cardiovascular status, the severity and duration of hypothyroidism, and concurrent medical conditions. Therapy is typically initiated at lower doses in elderly patients or those with underlying cardiac disease, with gradual titration based on periodic assessment of thyroid function tests (TSH levels).

General Administration Guidelines:

• Take Synthroid as a single daily dose, on an empty stomach, at least 30 to 60 minutes before breakfast.
• Administer with a full glass of water to aid swallowing and ensure quick gastric transit.
• Do not take concurrently with calcium carbonate, iron supplements, proton pump inhibitors, or certain other medications and foods, as they can significantly impair absorption. A spacing of at least 4 hours is generally recommended.
• Consistency in the timing of administration is crucial for maintaining stable hormone levels.

Pediatric dosing is based on body weight or body surface area and requires careful monitoring.

Precautions

• Cardiac Patients: Initiate therapy with caution in patients with cardiovascular diseases such as coronary artery disease, arrhythmias, or hypertension. Overtreatment can exacerbate angina, precipitate atrial fibrillation, or cause myocardial ischemia.
• Endocrine Disorders: Use with care in patients with disorders of the adrenal cortex (e.g., Addison’s disease) or pituitary insufficiency. Thyroid hormone therapy can precipitate an acute adrenal crisis if adrenal insufficiency is not first corrected.
• Osteoporosis: Prolonged overtreatment with levothyroxine may contribute to bone demineralization, increasing the risk of osteoporosis and fractures, particularly in postmenopausal women.
• Pregnancy & Lactation: Hypothyroidism during pregnancy is associated with risks to both mother and fetus. Thyroid hormone requirements frequently increase during pregnancy (often by 25-50%). Dosing must be carefully managed and monitored throughout pregnancy and postpartum. Synthroid is excreted in human milk but in amounts unlikely to affect the nursing infant; however, consultation with a physician is essential.
• Brand Substitution: Do not switch between different levothyroxine products (brand or generic) without consulting a physician and re-monitoring TSH levels, as bioequivalence may vary and necessitate dosage adjustment.

Contraindications

Synthroid is contraindicated in several specific clinical scenarios:

• Uncorrected adrenal insufficiency: Thyroid hormone increases tissue demand for adrenal hormones and can precipitate an Addisonian crisis.
• Untreated thyrotoxicosis (hyperthyroidism): Administration would exacerbate the condition.
• Acute myocardial infarction: Rapid hormone shifts can place undue stress on the compromised cardiovascular system.
• Hypersensitivity: Known hypersensitivity to any of the inactive ingredients in the Synthroid formulation. Allergic reactions are rare but possible.

Possible side effect

When dosed appropriately, Synthroid is generally well-tolerated as it simply replaces a deficient hormone. Side effects are almost exclusively associated with dosage exceeding the patient’s physiological requirements (iatrogenic hyperthyroidism).

Signs and symptoms of overdosage include:

• Cardiovascular: Palpitations, tachycardia (rapid heart rate), arrhythmias (e.g., atrial fibrillation), increased blood pressure, angina pectoris, heart failure.
• Central Nervous System: Headaches, tremors, nervousness, anxiety, irritability, insomnia, emotional lability.
• Gastrointestinal: Increased appetite, diarrhea, abdominal cramps, weight loss.
• Thermoregulatory: Heat intolerance, fever, excessive sweating.
• Musculoskeletal: Muscle weakness, muscle wasting, decreased bone density (with long-term overtreatment).
• Other: Menstrual irregularities, temporary hair loss (especially during the initial months of therapy or after dosage adjustments).

Drug interaction

Numerous drugs and supplements can interact with Synthroid, primarily affecting its absorption or metabolism.

Decreased Absorption:

• Calcium Carbonate: Commonly found in antacids and supplements.
• Iron Supplements and Multivitamins containing iron.
• Proton Pump Inhibitors (e.g., omeprazole) and H2 Blockers (e.g., ranitidine).
• Bile Acid Sequestrants: such as cholestyramine and colestipol.
• Sucralfate, Kayexalate (sodium polystyrene sulfonate), and Orlistat.
• Aluminum Hydroxide (found in some antacids).
• Foods: High-fiber diets, soybean flour (infant formula), cottonseed meal, and walnuts.

Altered Metabolism:

• Estrogen and Oral Contraceptives: Can increase thyroxine-binding globulin (TBG) levels, potentially increasing the dose requirement.
• Androgens and Anabolic Steroids: Can decrease TBG levels.
• Certain Antiseizure Medications: such as carbamazepine, phenytoin, and phenobarbital, can increase the metabolism of levothyroxine.
• Rifampin, Sertraline, and Chloroquine may also increase metabolism.
• Amiodarone: Can cause both hypothyroidism and hyperthyroidism and interacts complexly with thyroid hormone replacement.
• Diabetes Medications: Thyroid hormones may alter glycemic control, necessitating adjustment of insulin or oral hypoglycemic drugs.
• Warfarin (Coumadin): Thyroid hormones can potentiate the anticoagulant effect, increasing the risk of bleeding. Prothrombin time (INR) must be monitored closely.

A minimum 4-hour separation between Synthroid and these agents is typically recommended to avoid absorption issues.

Missed dose

If a dose is missed, it should be taken as soon as possible on the same day. If it is almost time for the next scheduled dose, the missed dose should be skipped. Do not take a double dose to make up for the missed one. Taking extra medication can cause symptoms of hyperthyroidism. Patients should maintain their regular dosing schedule and inform their physician of any significant pattern of missed doses, as this can affect the accuracy of thyroid function monitoring.

Overdose

An overdose of Synthroid manifests as thyrotoxicosis (a hypermetabolic state). Symptoms are those listed in the “Possible side effect” section and can be severe, including cardiac complications like tachyarrhythmias and cardiac arrest.

Management:

• In case of suspected overdose, contact a poison control center or emergency room immediately.
• Treatment is symptomatic and supportive. Beta-adrenergic blocking agents (e.g., propranolol) may be used to counteract sympathetic nervous system stimulation.
• There is no specific antidote. Levothyroxine is not effectively removed by dialysis.
• Plasma TSH and T4 levels should be monitored to guide therapy until the patient is clinically euthyroid.

Storage

• Store Synthroid tablets at controlled room temperature, 20°C to 25°C (68°F to 77°F), with excursions permitted between 15°C and 30°C (59°F and 86°F).
• Keep the medication in its original blister pack or bottle to protect it from light and moisture.
• Keep tightly closed.
• Keep out of reach of children and pets.
• Do not use medication beyond the expiration date printed on the container.

Disclaimer

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or medication. Never disregard professional medical advice or delay in seeking it because of something you have read here. The content has been compiled from various sources believed to be accurate but cannot be guaranteed. The manufacturer’s official prescribing information is the ultimate authority.

Reviews

• “As an endocrinologist with over 20 years of practice, I find Synthroid to be a reliable and predictable formulation for my patients. The consistent potency and wide range of available strengths allow for precise titration, which is critical for optimal patient outcomes.” – Dr. E. Lawson, MD
• “After being diagnosed with Hashimoto’s, it took some time to find the right dose of Synthroid. But once we did, the change was remarkable. My energy returned, the brain fog lifted, and I feel like myself again. I appreciate the consistency of a brand-name product.” – Sarah T.
• “The nursing staff finds the color-coded tablets extremely helpful for patient education and verifying medication administration, reducing the potential for errors in our clinic.” – Nurse J. Corbin, RN
• “I’ve been on Synthroid since my total thyroidectomy for cancer five years ago. My TSH levels have been stable and within target range on the same dose for three years. It gives me confidence in my ongoing health management.” – Michael R.