Levothroid is a brand of levothyroxine sodium, a synthetic version of the primary hormone produced by the thyroid gland (T4). It replaces or supplements natural thyroid hormone when your thyroid cannot make enough on its own.
Related topics: Thyroid, Hormones, Cancer, Sport, Other
What Levothroid is used for
Levothroid is primarily prescribed for hypothyroidism, a condition in which the thyroid gland is underactive. By restoring normal thyroid hormone levels, it helps relieve symptoms such as fatigue, weight gain, cold intolerance, and slowed metabolism.
Doctors may also use levothyroxine to:
- Suppress thyroid-stimulating hormone (TSH) after treatment for certain types of thyroid cancer
- Reduce the size of an enlarged thyroid (goiter), including goiter caused by iodine deficiency or autoimmune disease
- Support therapy following surgery or radioactive iodine ablation of the thyroid
Available strengths
Levothroid is available in multiple microgram strengths to allow precise dose adjustments:
- 112 mcg
- 50 mcg
- 200 mcg
- 25 mcg
- 100 mcg
- 75 mcg
- 125 mcg
Your exact dose is based on your TSH and free T4 blood tests, age, body weight, cardiac status, and whether you are pregnant.
How to take Levothroid
Many patients will need lifelong therapy. Do not stop or change your dose unless your prescriber tells you to. It can take 4 to 8 weeks to see the full effect after a dose change.
- Take once daily on an empty stomach, ideally in the morning 30 to 60 minutes before breakfast.
- Swallow capsules or tablets whole; do not cut, crush, or chew unless your specific product lists that it can be split.
- Avoid grapefruit and grapefruit juice with your dose. Separate levothyroxine from calcium, iron, magnesium, multivitamins, bile acid sequestrants, or soy-containing supplements by at least 4 hours.
- Be consistent: take it at the same time and in the same way every day.
For infants or those unable to swallow tablets, certain levothyroxine products can be given as a solution or dispersed per product instructions. Ask your pharmacist which formulation is appropriate.
Precautions and warnings
Before starting Levothroid, tell your clinician about all medical conditions. Extra caution or dose adjustments may be needed in people with:
- Heart disease or history of chest pain, arrhythmias, heart failure, or coronary artery disease
- Adrenal insufficiency (must be treated before starting levothyroxine)
- Untreated thyrotoxicosis (overactive thyroid)
- Osteoporosis or high fracture risk
- Diabetes (thyroid hormone can change insulin or oral med needs)
- Pituitary or hypothalamic disorders affecting TSH secretion
- Liver or kidney disease, severe hypoproteinemia, or porphyria
- Blood disorders including pernicious anemia or clotting history
Pregnancy and breastfeeding: Levothyroxine is the standard treatment for hypothyroidism in pregnancy and breastfeeding. Thyroid hormone needs often increase during pregnancy; monitoring and dose adjustments are common. If you become pregnant, contact your prescriber promptly for lab checks.
Important: Levothroid must not be used for weight loss in people with normal thyroid function. Using thyroid hormone for obesity is ineffective and potentially dangerous.
Contraindications
- Known hypersensitivity to levothyroxine or any product component
- Untreated adrenal insufficiency
- Untreated thyrotoxicosis
- Acute myocardial infarction (use only under close supervision if clinically indicated)
Patients with diabetes should track blood glucose closely when therapy starts or doses change. Report unusual highs or lows to your clinician.
Possible side effects
Seek urgent medical help for signs of severe reaction or overtreatment:
- Chest pain, pressure, or arm/jaw/back pain
- Fast, slow, or irregular heartbeat; palpitations; fainting
- Shortness of breath, difficulty swallowing, or neck vein distention
- Swelling of face, lips, tongue, or throat; hives or widespread rash
- Extreme fatigue, tremor, fever, heat intolerance
- Sudden severe headache, slurred speech, loss of coordination
Other effects that are usually less serious, especially if the dose is slightly high:
- Headache, nervousness, restlessness, rapid mood shifts
- Increased appetite, weight change, diarrhea, vomiting, stomach cramps
- Hair loss (often temporary when starting therapy)
- Feeling unusually warm or flushed, sweating
- Menstrual changes, trouble getting pregnant, muscle weakness
Contact your healthcare professional if bothersome effects persist or worsen.
Drug and food interactions
Always discuss all medicines and supplements with your prescriber or pharmacist. Important interactions include:
- Binding agents that reduce absorption: calcium or iron salts, aluminum/magnesium antacids, sucralfate, cholestyramine/colesevelam, sevelamer
- Enzyme inducers or inhibitors: certain anti-seizure drugs (carbamazepine, phenytoin), rifampin, amiodarone
- Warfarin and other anticoagulants (thyroid hormone may enhance anticoagulant effect)
- Proton pump inhibitors and H2 blockers (may affect absorption in some patients)
- Soy products and high-fiber diets (can reduce absorption; keep intake consistent)
- Grapefruit and grapefruit juice (avoid with dose)
Separate levothyroxine from interfering products by at least 4 hours. Consistency in diet and timing is essential for stable labs.
Missed dose
If you forget a dose, take it when you remember unless it is close to the time of your next dose. If it is almost time for the next dose, skip the missed dose and resume your regular schedule. Do not double up. If you miss doses frequently, speak with your clinician about strategies to improve adherence.
Overdose information
Symptoms of overdose can include agitation, confusion, sweating, rapid heart rate, chest pain, fainting, severe headache, slurred speech, cold clammy skin, and loss of consciousness. Call emergency services right away if overdose is suspected.
Storage
- Store at room temperature away from heat, moisture, and direct light.
- Keep in the original container with desiccant if provided; do not store in a humid bathroom.
- Do not freeze. Keep out of reach of children and pets.
Alternatives and similar medicines
Depending on clinical needs, your prescriber may consider these alternatives. Do not switch products without medical guidance; even small formulation differences can affect TSH.
- Other levothyroxine brands/formulations: Synthroid, Levoxyl, Unithroid, Tirosint (gel capsule), Tirosint-SOL (oral solution)
- Liothyronine (T3): Cytomel brand or generic liothyronine; sometimes used alone in special cases or combined with T4 for select patients
- Desiccated thyroid extract: Armour Thyroid, NP Thyroid; contains both T4 and T3 in fixed ratios; variability and T3 content make precise dosing more challenging
- Generic levothyroxine: multiple manufacturers; effective and lower cost for many patients
Clinical notes:
- Most patients do well on levothyroxine alone (T4). Combination T4/T3 is reserved for specific scenarios after careful evaluation.
- For thyroid cancer suppression, brand consistency and tight TSH control are often prioritized.
Typical prices in the USA
Prices vary by pharmacy, dose, quantity, and insurance. Approximate cash prices for a 30-day supply:
- Generic levothyroxine tablets: about $4 to $15 (many discount programs available)
- Brand Synthroid/Levoxyl/Unithroid: roughly $20 to $60
- Tirosint (gel capsule): about $120 to $180
- Tirosint-SOL (solution): about $140 to $200
- Generic liothyronine: about $10 to $40; Cytomel brand: about $60 to $120
- Desiccated thyroid (Armour, NP Thyroid): about $20 to $60
Tip: Ask your pharmacist about generics, discount cards, and 90-day supplies, which can significantly reduce costs.
U.S. legal and access information
- Status: Levothroid (levothyroxine) is an FDA-approved prescription-only (Rx) medication in the United States.
- Prescription requirement: A valid prescription from a licensed U.S. prescriber is required for dispensing, including via online pharmacies. Legitimate online pharmacies will verify your prescription.
- Importation: Personal importation of prescription drugs is generally restricted. The FDA may exercise discretion in limited cases, but routine importation of approved drugs available in the U.S. is discouraged and can be detained by customs.
- Generic substitution: State laws typically allow pharmacists to substitute an FDA-approved generic unless the prescriber indicates brand medically necessary. For thyroid therapy, many clinicians prefer staying on the same manufacturer once stabilized.
- Monitoring: Periodic TSH and free T4 testing is standard. Dose changes should be made only under medical supervision.
- Sports and anti-doping: Levothyroxine (T4) and liothyronine (T3) are not on the WADA Prohibited List at the time of writing. Athletes should still disclose use to team medical staff and comply with any event-specific rules.
- Driving and work: When properly dosed, levothyroxine does not impair alertness. If symptoms like palpitations or tremor occur, seek medical advice before operating machinery.
Safety reminder: Never use thyroid hormones for weight loss if your thyroid function is normal; misuse can cause serious heart and bone problems.
This information is educational and does not replace the advice of your healthcare professional. Always follow your prescriber's instructions and the patient information that comes with your medicine.
