Levothyroxine Dosage

Medically reviewed by Drugs.com. Last updated on Feb 6, 2024.

Usual Adult Dose for Hypothyroidism

Dosing should be individualized with consideration given to age, cardiovascular status, concomitant medical conditions (including pregnancy), and specific nature of condition; follow clinical response and laboratory parameters closely as dose is adjusted:

INITIAL DOSES:
Primary Hypothyroidism: For otherwise healthy individuals in whom growth and puberty are complete:
Initial dose: 1.6 mcg/kg orally once a day

• Adjust dose in 12.5 to 25 mcg increments every 4 to 6 weeks until clinically euthyroid and TSH returns to normal

Individuals over 50 years and/or Patients with Cardiovascular Disease:
Initial dose: 12.5 to 25 mcg orally once a day

• Adjust dose at 6 to 8-weeks intervals until clinically euthyroid and TSH returns to normal

Severe Longstanding Hypothyroidism:
Initial dose: 12.5 to 25 mcg orally once a day

• Adjust dose in increments of 12.5 to 25 mcg/day every 2 to 4 weeks until clinically euthyroid and TSH returns to normal

MAINTENANCE DOSE: Approximately 1.6 mcg/kg/day is a full replacement dose
MAXIMUM dose: 200 to 300 mcg/day (doses greater than 200 mcg/day are seldom needed; doses greater than 300 mcg/day are rarely needed and may indicate poor compliance, malabsorption, drug interactions, or a combination of these factors)

Secondary (PITUITARY) OR Tertiary (HYPOTHALAMIC) Hypothyroidism:

• Dosing as described above except serum free-T4 level will be used to monitor therapy; serum TSH levels are not a reliable measure and should not be used
• Titrate until clinically euthyroid and serum free-T4 levels are restored to the upper half of the normal range

Comments:

• Dose should be individualized with regular monitoring of clinical status and laboratory parameters.
• Peak effect of a given dose may not be attained for 4 to 6 weeks.
• Not indicated for the treatment of hypothyroidism during the recovery phase of subacute thyroiditis.
• Co-administered food and concomitant medications may significantly affect absorption; take on an empty stomach and at least 4 hours before or after drugs known to interfere with levothyroxine absorption.

Use: As replacement therapy in primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) congenital or acquired hypothyroidism

Usual Adult Dose for TSH Suppression

TSH levels should generally be suppressed to below 0.1 IU/L

• A dose greater than 2 mcg/kg orally once a day is usually required to achieve this degree of suppression

Comments:

• Patients with high-risk tumors may target a greater level of TSH suppression, however, this is not well defined.
• This drug is not indicated for suppression of benign thyroid nodules and nontoxic diffuse goiter in iodine-sufficient patients as there are no clinical benefits and overtreatment may induce hyperthyroidism.

Use: As an adjunct to surgery and radioiodine therapy in the management of thyrotropin-
dependent well-differentiated thyroid cancer.

Usual Adult Dose for Myxedema Coma

Parenteral Formulation:

• Initial loading dose: 300 to 500 mcg IV once
• Maintenance dose: 50 to 100 mcg IV once a day until patient can tolerate oral therapy

Comment:

• Age, general physical condition, cardiac risk factors, severity and duration of myxedema coma should be considered when determining the initial and maintenance dosages.
• The relative bioavailability between oral and IV levothyroxine is estimated to be 48% to 74%; due to individual differences, TSH levels should be measured and doses adjusted accordingly.

Use: For the treatment of myxedema coma.

Usual Geriatric Dose for Hypothyroidism

Initial dose: 12.5 to 25 mcg orally once a day

• Adjust dose at 6 to 8-weeks intervals until clinically euthyroid and TSH returns to normal

Maintenance dose: Full replacement doses may be less than 1 mcg/kg/day
Maximum dose: 200 to 300 mcg/day (doses greater than 200 mcg/day are seldom needed; doses greater than 300 mcg/day are rarely needed and may indicate poor compliance, malabsorption, drug interactions, or a combination of these factors)

Comments:

• Dosing should be individualized with consideration given to age, cardiovascular status, concomitant medical conditions, and the specific nature of condition; follow clinical response and laboratory parameters closely as dose is adjusted.
• Peak effect of a given dose may not be attained for 4 to 6 week; full recovery dose s.
• Not indicated for the treatment of hypothyroidism during the recovery phase of subacute thyroiditis.
• Co-administered food and concomitant medications may significantly affect absorption; take on an empty stomach and at least 4 hours before or after drugs known to interfere with levothyroxine absorption.

Use: As replacement therapy in primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) congenital or acquired hypothyroidism

Usual Pediatric Dose for Hypothyroidism

0 to 3 months: 10 to 15 mcg/kg orally once a day
3 to 6 months: 8 to 10 mcg/kg orally once a day
6 to 12 months: 6 to 8 mcg/kg orally once a day
1 to 5 years: 5 to 6 mcg/kg orally once a day
6 to 12 years: 4 to 5 mcg/kg orally once a day
12 years or older and incomplete growth and puberty: 2 to 3 mcg/kg orally once a day
12 years or older with growth and puberty complete: 1.6 mcg/kg orally once a day

Newborns (0 to 3 months) at Risk for Cardiac Failure: Consider a lower initial dose; increase dose every 4 to 6 weeks as needed based on clinical and laboratory response

Pediatric Patients at Risk for Hyperactivity: Initial dose should be one-fourth the recommended full replacement dose; increase weekly by one-fourth to the full recommended replacement dose

Comments:

• Dose should be individualized with regular monitoring of clinical status and laboratory parameters; peak effect may not be attained for 4 to 6 weeks.
• Not indicated for the treatment of hypothyroidism during the recovery phase of subacute thyroiditis.
• Co-administered food and concomitant medications may significantly affect absorption; take on an empty stomach and at least 4 hours before or after drugs known to interfere with levothyroxine absorption.
• The capsule formulation is indicated for patients 6 years or older as the capsule should be swallowed whole; see Other Comment/Administration Advice for specific administration instructions including instructions for those unable to swallow intact tablets.

Use: For the treatment of congenital or acquired hypothyroidism.

Renal Dose Adjustments

No adjustment recommended

Liver Dose Adjustments

No adjustment recommended

Dose Adjustments

Myxedema Coma: Elderly and Patients with Cardiovascular Disease: IV use is associated with cardiac toxicity, therefore, doses at the lower end of the dose range should be used in these populations.

Pregnancy:
New Onset Hypothyroidism:

• Patients with moderate to severe signs and symptoms of hypothyroidism: 1.6 mcg/kg orally once a day
• Patients with mild hypothyroidism (TSH less than 10 mIU/L): 1 mcg/kg orally once a day
• Evaluate TSH every 4 weeks and adjust dose until serum TSH is within trimester-specific range Preexisting Hypothyroidism:
• Monitor TSH and free T4 as soon as pregnancy is confirmed and at least each trimester
• Maintain TSH in trimester-specific reference range (primary hypothyroidism)
• If serum TSH is above the normal trimester-specific range, increase by 12.5 to 25 mcg/day and measure TSH every 4 weeks until serum TSH is within the normal trimester-specific range
• Reduce to pre-pregnancy dose immediately after delivery and measure serum TSH level 4 to 8 weeks postpartum to ensure dose is appropriate

Therapeutic drug monitoring/range:

• Primary Hypothyroidism: Monitor TSH
• Secondary and Tertiary Hypothyroidism: Monitor serum free-T4 levels (maintain in the upper half of the normal range)

Precautions

US BOXED WARNING: NOT FOR TREATMENT OF OBESITY OR FOR WEIGHT LOSS

• Thyroid hormones, either alone or with other agents, should not be used for the treatment of obesity or for weight loss. In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction. Larger doses may produce serious or even life threatening manifestations of toxicity, particularly when given in association with sympathomimetic amines such as those used for their anorectic effects.

NARROW THERAPEUTIC INDEX:

• This drug should be considered a narrow therapeutic index (NTI) drug as small differences in dose or blood concentrations may lead to serious therapeutic failures or adverse drug reactions.

Recommendations:

• Generic substitution should be done cautiously, if at all, as current bioequivalence standards are generally insufficient for NTI drugs.
• Additional and/or more frequent monitoring should be done to ensure receipt of an effective dose while avoiding unnecessary toxicities.

CONTRAINDICATIONS:

• Uncorrected adrenal insufficiency

Consult WARNINGS section for additional precautions.

Dialysis

Very little drug is removed by dialysis because T4 is highly protein bound.

Other Comments

Administration advice:

• Take orally once a day on an empty stomach, preferably one-half to 1 hour before breakfast
• Drugs that can decrease the absorption of levothyroxine should not be taken within 4 hours (e.g., iron, calcium supplements, antacids)

CAPSULES: For patients 6 years or older; Swallow whole; do not crush, chew, or cut
LEVO-T Tablets: Take with a full glass of water as tablet may rapidly disintegrate
THYQUIDITY Oral Solution: Use calibrated oral syringe to measure and administer dose
TIROSINT-SOL Oral Solution in Unit Dos Ampules: May dilute or mix in water prior to administering OR squeeze directly into mouth or onto a spoon; do not mix or dilute with any liquid other than water

For Administration to Infants and Children Unable to Swallow Intact Tablets:

• Crush tablet and suspend in a small amount (5 to 10 mL) of water
• Immediately administer by spoon or dropper; do not store suspension
• Do not administer in foods that decrease absorption such as soybean-based infant formula

Storage requirements:

• Oral Capsules and Tablets: Protect from light and moisture; store at 25C (77F) excursions permitted 15C to 30C (59F to 86F)
• Oral Solution: Protect from light; store at 20C to 25C (68F to 77F); use within 8 weeks of opening bottle
• Oral solution in unit dose ampules: Keep ampules in pouch until ready to use; all ampules should be used within 15 days of opening pouch
• Vial: Protect from light; Store unopened vial at 20C to 25C (68F to 77F)

Reconstitution/preparation techniques:

• Vial: Reconstitute with 5 mL of 0.9% Sodium Chloride Injection; shake to ensure complete mixing; resulting concentration: 20 mcg/mL (100 mcg) and 100 mcg/mL (500 mcg); preservative free; stable for 4 hours; discard unused portion

IV compatibility: Do not add to other IV fluids

General:

• When regularly administered within 1 hour of foods that may affect absorption, evaluate the need for dose adjustments.
• This drug is not indicated for suppression of benign thyroid nodules and nontoxic diffuse goiter in iodine-sufficient patients as there are no clinical benefits and overtreatment may induce hyperthyroidism.
• The relative bioavailability between parenteral and oral levothyroxine products has not been established; use caution

when switching patients between oral and parenteral product as accurate dosing conversion has not been studied.

• This drug is not indicated for treatment of hypothyroidism during the recovery phase of subacute thyroiditis.
• This drug should not be used alone or with other agents for treatment of obesity or for weight loss.
• Delays in diagnosis and institution of therapy may have deleterious effects on intellectual and physical growth and development.

Monitoring: Closely monitor to avoid over and undertreatment:

• Adults: Primary Hypothyroidism: Monitor serum TSH 6 to 8 weeks following initiation and with any change in dose; once stabilized, evaluate clinical and biochemical response every 6 to 12 months or whenever there is a change in dose or clinical status.
• Pediatrics: Congenital or Acquired Hypothyroidism: Measure serum TSH and total or free-T4 at 2 and 4 weeks following therapy initiation, 2 weeks after any dose change, and every 3 to 12 months following dose stabilization until growth is complete; poor compliance or abnormal values may require more frequent monitoring. Regular clinical examination should include assessment of development, mental and physical growth, and bone maturation.
• Pediatrics: TSH may not normalize in some patients due to in utero hypothyroidism causing a resetting of the pituitary-thyroid feedback; failure of serum T4 to increase into the upper half of the normal range within 2 weeks of initiation of therapy and/or of the serum TSH to decrease below 20 mIU/L within 4 weeks may indicate inadequate therapy; assess compliance, dose, and method of administration prior to increasing the dose
• Secondary (pituitary) and Tertiary (hypothalamic) Hypothyroidism: Monitor serum free-T4 levels and maintain in the upper half of the normal range
• In patients with diabetes, monitor glycemic control after starting, changing, or discontinuing therapy.
• Closely monitor TSH levels during pregnancy.
• Monitor for cardiac arrhythmias during surgical procedures in patients with coronary artery disease.

Patient advice:

• Patients should be instructed to read the US FDA-approved patient labeling.
• Patients should be instructed to take this drug on an empty stomach, preferably in the morning at least one-half hour before breakfast.
• Patients should understand it may take several weeks before an improvement symptoms occurs; laboratory tests will be needed to monitor therapy.
• Patients should be instructed to notify their healthcare provider if they experience any of the following symptoms: rapid or irregular heartbeat, chest pain, shortness of breath, leg cramps, headache, nervousness, irritability, sleeplessness, tremors, change in appetite, weight gain or loss, vomiting, diarrhea, excessive sweating, heat intolerance, fever, changes in menstrual periods, hives or skin rash, or any other unusual medical event.
• Patients should understand that partial hair loss may occur rarely during the first few months of therapy, but this is usually temporary.
• Patients should be instructed to notify their healthcare provider if they are planning to or become pregnant.

Frequently asked questions

• Does levothyroxine cause weight gain or loss?
• What can I eat for breakfast after taking levothyroxine?
• Can I take other medications with levothyroxine?
• Does levothyroxine cause hair loss?
• How long after taking levothyroxine can you drink milk?
• How long does levothyroxine stay in your system?
• How soon after taking levothyroxine can I take omeprazole?
• What is the difference between Levoxyl and Synthroid?
• What happens if you stop taking levothyroxine?

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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