Levothyroxine dosage
Levothyroxine has no standard dose. The FDA label anchors full replacement at approximately 1.6 mcg per kg per day, but the actual number is set by your prescriber from your serum TSH and re-set every time TSH moves. This matters more than with most drugs: levothyroxine is a narrow-therapeutic-index medicine, meaning a 12-25 mcg difference — one step on the label's strength ladder — can move a patient from euthyroid to hyperthyroid. This page is a reference to what the FDA-approved label actually says. It is not a dosing recommendation, and we do not sell levothyroxine or any thyroid product.
This is reference, not a dosing instruction. Levothyroxineis prescription-only and the dose is individualized and titrated by a prescriber to your condition, response, kidney/liver function and other medicines. The figures below are the FDA label’s — do not start, change or stop a dose based on this page.
Approved for: Levothyroxine sodium is FDA-approved as replacement therapy in primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) hypothyroidism in adults and pediatric patients, including neonates. It is also approved as an adjunct to surgery and radioiodine therapy in the management of well-differentiated thyroid cancer (TSH suppression). It is NOT approved for obesity or weight loss.
Available as: Oral tablets in 12 strengths: 25, 50, 75, 88, 100, 112, 125, 137, 150, 175, 200, and 300 mcg. The unusually fine strength ladder exists because levothyroxine has a narrow therapeutic index — the difference between 100 mcg and 112 mcg is clinically meaningful, which is why the label supplies increments most drugs never need.
| Use | What the label says |
|---|---|
| Hypothyroidism — healthy adults (full replacement) | The FDA label states: "The average full replacement dose of SYNTHROID is approximately 1.6 mcg per kg per day (for example: 100 to 125 mcg per day for a 70 kg adult)." This is a starting estimate for otherwise healthy adults without cardiac disease, not a target. The label directs that the dose then be adjusted by 12.5 to 25 mcg increments every 4 to 6 weeks until the patient is clinically euthyroid and serum TSH returns to normal. Residual thyroid function, age, body weight, and other drugs all shift the final number away from the 1.6 mcg/kg estimate. |
| Older adults / cardiovascular disease — start low | The label carves out a much lower start: "For elderly patients or patients with underlying cardiac disease, start with a dose of 12.5 to 25 mcg per day." Titration is also slower — the dose is increased every 6 to 8 weeks (not 4 to 6) as needed until the patient is clinically euthyroid and serum TSH normalizes. The reason is cardiac: too-fast replacement in a patient with coronary artery disease can precipitate angina or arrhythmia. The label also notes that full replacement in elderly patients may be less than 1 mcg per kg per day — so applying the 1.6 mcg/kg figure to an 80-year-old would overshoot. |
| Titration & monitoring — TSH recheck timing | The label instructs: "In adult patients with primary hypothyroidism, monitor serum TSH levels after an interval of 6 to 8 weeks after any change in dose." This interval is not arbitrary — levothyroxine's long half-life means serum levels need roughly that long to reach a new steady state, so a TSH drawn at 2 or 3 weeks after a dose change will mislead. Once a stable dose is reached, TSH is rechecked periodically and any time clinical status, weight, pregnancy status, or interacting medications change. In secondary or tertiary hypothyroidism, TSH is not a valid monitoring target and free-T4 is used instead. |
| Pediatric dosing (per FDA label, mcg/kg/day) | The label gives weight-based pediatric daily doses by age: 0-3 months, 10-15 mcg/kg/day; 3-6 months, 8-10 mcg/kg/day; 6-12 months, 6-8 mcg/kg/day; 1-5 years, 5-6 mcg/kg/day; 6-12 years, 4-5 mcg/kg/day; over 12 years with growth and puberty incomplete, 2-3 mcg/kg/day; growth and puberty complete, 1.6 mcg/kg/day. Congenital hypothyroidism is treated urgently because untreated thyroid deficiency in infancy causes irreversible neurodevelopmental harm. Pediatric dosing is a specialist matter and is included here only as a reference to what the label states. |
| Pregnancy | The label notes that levothyroxine requirements commonly increase during pregnancy and directs that TSH be measured and the dose adjusted using trimester-specific reference ranges, with monitoring each trimester. Untreated or under-treated maternal hypothyroidism carries fetal risk, so levothyroxine is continued in pregnancy — the question is dose, not whether to take it. Dose adjustment in pregnancy must be prescriber-directed. |
Maximum dose
The FDA label sets no fixed maximum daily dose for levothyroxine. Unlike most drugs, the ceiling is biochemical rather than numeric: the correct dose is the one that normalizes serum TSH (or, for thyroid cancer TSH-suppression therapy, achieves the target degree of suppression), and anything above that is over-replacement by definition. The label makes the point under bone density (§5.6), not the cancer indication: "Administer the minimum dose of SYNTHROID that achieves the desired clinical and biochemical response to mitigate this risk." It also gives two anchors: "Doses greater than 200 mcg per day are seldom required" and "An inadequate response to daily doses of greater than 300 mcg per day is rare and may indicate poor compliance, malabsorption, drug interactions, or a combination of these factors." In practice most adults land near 1.6 mcg/kg/day, but a patient needing far more than that is usually a signal of a malabsorption problem, an interacting drug, or missed doses — not a reason to keep escalating. Escalating dose without TSH confirmation is the specific behavior the boxed warning exists to prevent.
Dose adjustments
Older adults and anyone with cardiac disease start at 12.5-25 mcg with 6-8 week titration steps, and may need less than 1 mcg/kg/day at full replacement. Pregnancy typically increases requirements, with TSH checked each trimester against trimester-specific ranges. Absorption is the other major variable: the label directs that levothyroxine be given at least 4 hours before or after drugs known to interfere with its absorption, naming calcium carbonate and ferrous sulfate among them; antacids, sucralfate, bile acid sequestrants such as cholestyramine, and proton pump inhibitors (which raise gastric pH) can all reduce absorption. Because levothyroxine has a narrow therapeutic index, changes that would be trivial for another drug — a new calcium supplement, a switch in manufacturer, a change in when you eat breakfast — can move TSH out of range. The label advises re-checking TSH after such changes rather than assuming the dose still fits.
Dosing safety — read before you rely on any number
BOXED WARNING: "Thyroid hormones, including SYNTHROID, either alone or with other therapeutic agents, should not be used for the treatment of obesity or for weight loss." The label continues that in euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction, and that larger doses may produce serious or even life-threatening manifestations of toxicity, particularly when given together with sympathomimetic amines such as those used for their anorectic effects. This is the single most important thing on the label. Beyond it: over-replacement causes real harm even when it feels like more energy — the label associates excess thyroid hormone with cardiac effects including palpitations, tachycardia, arrhythmias, raised pulse and blood pressure, angina and heart failure, and with increased bone resorption and reduced bone mineral density, particularly relevant in postmenopausal women. Administration is part of the dose: take on an empty stomach, one-half to one hour before breakfast (the label’s wording; taking it with water is ordinary practice, not a label instruction). Taking it with food or coffee lowers absorption and can make a correct prescription behave like an underdose.
Bottom line
There is no normal levothyroxine dose you can look up and apply. The label's 1.6 mcg/kg/day is a starting estimate for healthy adults; older adults and cardiac patients start at 12.5-25 mcg and move slower; the real dose is whatever brings your TSH into range, confirmed 6-8 weeks after each change. Two habits protect that dose more than anything else: take it on an empty stomach 30-60 minutes before breakfast with water, keeping calcium and iron 4 hours away, and keep your product consistent — brands and generics are not interchangeable by feel, so tell your prescriber if your pharmacy switches you and ask whether TSH should be rechecked. Never adjust the dose yourself, and never take it for weight loss.
Frequently asked questions
What is the normal dose of levothyroxine?
There isn't one fixed normal dose — the FDA label gives an estimate, not a standard. For healthy adults needing full replacement the label states the average full replacement dose is approximately 1.6 mcg per kg per day, giving 100 to 125 mcg per day for a 70 kg adult as its own example. But older adults and people with cardiac disease start far lower, at 12.5 to 25 mcg per day, and elderly patients may need less than 1 mcg/kg/day even at full replacement. The dose that is right for you is the one that normalizes your serum TSH, which only a blood test can identify.
How is the levothyroxine dose calculated by weight?
The label's adult figure is approximately 1.6 mcg per kg of body weight per day — so a 70 kg (154 lb) adult lands around 100 to 125 mcg per day, which is the label's own worked example. Pediatric dosing is more weight-intensive and drops with age: 10-15 mcg/kg/day at 0-3 months, 8-10 at 3-6 months, 6-8 at 6-12 months, 5-6 at 1-5 years, 4-5 at 6-12 years, 2-3 over age 12 while growth is incomplete, and 1.6 mcg/kg/day once growth and puberty are complete. Treat the weight calculation as a starting point only. It is not a target — the label directs that the dose then be titrated against TSH, and plenty of patients end up meaningfully above or below their calculated figure.
What is the best time to take levothyroxine?
The FDA label directs that it be administered "as a single daily dose, on an empty stomach, one-half to one hour before breakfast." The consumer guidance from MedlinePlus says the same thing: once a day on an empty stomach, 30 minutes to 1 hour before breakfast. The reason is absorption — food, coffee, and certain supplements meaningfully reduce how much levothyroxine reaches your bloodstream. What matters nearly as much as the timing itself is consistency: because the dose is titrated to a TSH drawn under your usual habits, changing when or how you take it can shift your TSH even though the prescription hasn't changed.
How long until a dose change shows up on TSH?
About 6 to 8 weeks. The FDA label instructs that in adult patients with primary hypothyroidism, serum TSH be monitored after an interval of 6 to 8 weeks after any change in dose. Testing earlier than that is a common and misleading mistake — levothyroxine's long half-life means the drug needs roughly that long to reach a new steady state, so an early TSH can prompt a dose change that wasn't actually needed. Symptom improvement can also lag the lab, so feeling unchanged at three weeks is not evidence the new dose is wrong. In elderly and cardiac patients, dose increases themselves are spaced at the same 6 to 8 week interval.
Can I take levothyroxine with coffee or calcium?
No — not at the same time. The label directs that levothyroxine be given at least 4 hours before or after drugs known to interfere with its absorption, and names calcium carbonate and ferrous sulfate (iron) among them; MedlinePlus states the same 4-hour rule for calcium and iron supplements as well as cholestyramine. Antacids, sucralfate, and proton pump inhibitors can also reduce absorption. Coffee is a separate but real problem: because the label requires an empty stomach 30-60 minutes before breakfast, the morning coffee that many people take the pill with cuts absorption. The practical version: pill with plain water on waking, then wait 30-60 minutes for coffee and breakfast, and push calcium and iron to a different part of the day entirely.
What happens if the levothyroxine dose is too high?
Over-replacement produces hyperthyroidism, and the harm is real even though the early symptoms can feel like more energy. The label links excess thyroid hormone to cardiac effects including palpitations, tachycardia, arrhythmias, increased pulse and blood pressure, angina, heart failure, myocardial infarction and cardiac arrest, and to increased bone resorption with reduced bone mineral density — a particular concern in postmenopausal women on long-term therapy. MedlinePlus lists chest pain, rapid or irregular heartbeat, uncontrollable shaking, nervousness, anxiety, insomnia and shortness of breath as signs of too much. This is also why the boxed warning forbids using thyroid hormone for weight loss: larger-than-replacement doses can cause serious or life-threatening toxicity, especially alongside stimulant appetite suppressants. If you have these symptoms, contact your prescriber for a TSH — do not cut the dose on your own.
Sources
More guides for Levothyroxine
Other dosage guides: Metformin dosage · Amoxicillin dosage · Prednisone dosage · Gabapentin dosage · Ibuprofen dosage · Lisinopril dosage · Omeprazole dosage · Doxycycline dosage · Ondansetron dosage · Albuterol dosage · Allopurinol dosage · Methotrexate dosage · Alendronate dosage · Fluconazole dosage · Acetaminophen dosage · Diphenhydramine dosage · Naproxen dosage · Aspirin dosage · Cetirizine dosage · Dimenhydrinate dosage · Famotidine dosage.
Doses are transcribed from the FDA-approved label and are general reference information, not medical advice or a personal dose. Only a prescriber can set or change your dose. If you think you took too much, contact Poison Control (1-800-222-1222) or 911.