levothyroxine Uses, Dosage, Side Effects, Precautions & Warnings

what is levothyroxine used for

Generic drug of the Therapeutic class: Endocrinology
active ingredients: Levothyroxine sodium

what is levothyroxine used for and  indication?

  • Hypothyroidism.
  • Circumstances, associated or not with hypothyroidism, where it is necessary to curb the TSH.

levothyroxine dosage


The doses administered vary according to the degree of hypothyroidism, the age of the patient and individual tolerance. Hypothyroidism being in the majority of cases, a definitive disease, treatment should be continued indefinitely.

levothyroxine dosage adults

  • In general the dosage should be established gradually starting for example, at 25 or 50 μg per day; the daily dose will then be increased in increments of 25 to 50 μg approximately 2 to 4 weeks apart;
  • In general, hormone replacement therapy requires an average of 100 to 150 μg once a day in the morning on an empty stomach;
  •  More gradual dosing regimens may also be proposed in particular, in cases of heart failure or coronary heart failure, rhythm disorders, in patients with severe or persistent hypothyroidism and in the elderly, for whom it is appropriate to start treatment at lower doses and to respect more progressive levels. A maintenance dose below the dose required to normalize the TSH level may be considered.
  •  In acute post-surgical hypothyroidism in the absence of underlying cardiac pathology, treatment can be initiated from the outset at 1 μg / kg / day as a single substitution and at 2 μg / kg / day as a treatment with a cold target. (by adjusting the dose later).
  • The average doses are 1.7 μg / kg / day for replacement therapy and 2.1 to 2.5 μg / kg / day for treatment with freezing;
  •  In combination with synthetic antithyroid drugs for the treatment of Graves’ disease, the dosage is 25 to 125 μg to be adapted to the biological results;
  • The dosage should be adjusted according to TSH results, after approximately 6 to 8 weeks of constant dosing. An additional free T4 assay is required for the treatment of patients with thyroid cancer for the purpose of treatment. In other cases (suspected non-adherence, prescription amiodarone or unexplained hypothyroidism), other free T4 determinations may be appropriate. Patient monitoring will focus on the clinic with signs of overdose (nervousness, tachycardia, insomnia) and biological tests. In equilibrium, if the clinical state is stable, a dosage once or twice a year is sufficient.
  • Particular case of patients with central hypothyroidism (pituitary insufficiency): the TSH assay is non-contributory and should be replaced by the assay of free T4.

levothyroxine dose in child

  • The maintenance dose is usually 100 to 150 μg / m2 body surface area per day.
  • For neonates and infants with congenital hypothyroidism for whom it is important to initiate replacement therapy quickly, the recommended starting dose is 10 to 15 μg / kg body weight per day for the first 3 months. Thereafter, the dose should be adjusted according to clinical outcomes and thyroid hormone and TSH levels.
  • For children with acquired hypothyroidism, the recommended starting dose is 12.5 to 50 μg / day. The dose should be increased gradually every 2 to 4 weeks depending on the clinical results and thyroid hormone and TSH levels until the dose for complete substitution is reached.

Administration mode

In children:

  • This treatment should be given only to children who can swallow tablets.
  • For infants, the total daily dose should be given if possible at least 1/2 hour before the first meal of the day.

how levothyroxine works in the body?

Pharmacotherapeutic group: thyroid medications, ATC code: H03AA01

  • Thyroid hormone, chemically defined in its natural form L more active than form D.
  • Levothyroxine essentially increases tissue oxygen consumption, basic metabolism, heart rate.

What are the side effects of levothyroxine?

  • Aggravation of any cardiopathy (heart failure, angina, rhythm disorders …).
  •  Signs of hyperthyroidism, such as tachycardia, tremors, cardiac arrhythmias, insomnia, excitability, elevated temperature, sweating, rapid weight loss, diarrhea, should be used for hormonal dosing, decrease or discontinue treatment for several days. will then be resumed at lower doses.
  • In children, possibility of hypercalciuria.
  •  Hypersensitivity reactions to excipients and / or the active substance have been reported. The most common signs and symptoms are: urticaria, pruritus, angioedema, dyspnea, erythema.

Reporting of suspected adverse reactions

levothyroxine Interactions

Association subject to precautions for use

 Ion exchange resins (colestyramine, cholestipol, kayexalate, …) sevelamer, sucralfate,gastrointestinal topical agents , antacids (aluminum salts …) and adsorbents

Decreased activity of thyroid hormones (reduction of intestinal absorption).

Take them away from thyroid hormones (more than 2 hours if possible).

Enzyme inducers

  • Anticonvulsants (carbamazepine, phenobarbital, phenytoin, primidone, barbiturates); griseofulvin; rifampicin, rifabutin. Described for phenytoin, rifampicin and carbamazepine.
  • Risk of clinical hypothyroidism in hypothyroid patients when using combinations due to increased metabolism of T3 and T4.
  • Monitoring of serum T3 and T4 levels and adjustment of thyroid hormone dosage if necessary during enzyme inducer treatment and after discontinuation.

Drugs containing iron salts, oral calcium

  • Decreased digestive absorption of levothyroxine.
  • Take Levothyroxine away from these products (more than 2 hours, if possible).

Chloroquine / proguanil

  • Risk of clinical hypothyroidism in patients substituted by thyroid hormones.
  • Monitoring of TSH and serum T3 and T4 concentrations and adaptation, if necessary, of thyroid hormone dosage during antimalarial treatment and after discontinuation.

Protease inhibitors boosted by ritonavir (indinavir, lopinavir …)

  • Protease inhibitors can decrease the effectiveness of thyroid hormones by increasing their hepatic metabolism. It is recommended to closely monitor thyroid hormone levels (clinical and laboratory monitoring) and if necessary adjust the dose of levothyroxine.

Non-contraceptive estrogens

  • Risk of clinical hypothyroidism in estrogen replacement therapy. In this case, clinical and biological monitoring is necessary; the dose of levothyroxine should be adjusted in postmenopausal women taking estrogens.

Associations to consider

Imatinib, sunitinib

  • Imatinib and sunitinib may decrease the effectiveness of levothyroxine. It is therefore recommended to monitor any changes in the thyroid function of patients, at the initiation or at the end of the concomitant treatment. The dose of levothyroxine will be adjusted if necessary.


  • Orlistat may interact with thyroid hormone replacement therapy by decreasing the absorption of thyroid hormones.

levothyroxine Warnings and Precautions

levothyroxine warnings

  • Obesity is not an indication of thyroid hormones used alone or in combination unless this obesity is associated with true hypothyroidism. Their administration at high doses or in combination with amphetamine substances can be dangerous.
  • The effectiveness of the treatment and the possible signs of intolerance can appear only after a latency period of the order of 15 days to a month.

Precautions for use

  • The quality of the therapeutic balance must be controlled by an adequate endocrinological evaluation.
  • In case of cardiac pathology balanced by the treatment (coronary disorders, rhythm disorders), the indication is to be discussed on a case by case basis. If the treatment is instituted, the substitution is limited to obtaining a TSH in the high normal values. The surveillance of the subjects must be particularly attentive. Persistent or aggravated hypertension with levothyroxine should lead immediately to appropriate management.
  • If there is a risk of adrenocortical insufficiency (in particular, hypothyroidism of pituitary origin), treatment with hydrocortisone should be instituted beforehand.
  • Soy can decrease intestinal absorption of levothyroxine. Therefore, a reassessment of the Levothyrox dosage may be necessary especially at the beginning or end of a soy supplementation.
  • When switching from one levothyroxine sodium medication to another, it is important to monitor the therapeutic balance in certain at-risk patients in the following categories: patients who are receiving treatment for thyroid cancer but who have also cardiovascular disease (heart or coronary heart failure, and rhythm disorders), pregnant women, children and the elderly; and in some situations where the therapeutic balance has been particularly difficult to achieve.
  • In these patients, the maintenance of the therapeutic balance must be confirmed by a clinical evaluation, or even biological if necessary (by a control of the TSH carried out between 6 and 8 weeks after the substitution, except for the pregnant women where the modalities of surveillance to be adapted according to the evolution of the thyroid pathology and the term of the pregnancy).
  • In postmenopausal women with hypothyroidism and a high risk of osteoporosis, supra-physiologic levels of levothyroxine should be avoided. This is why close monitoring of thyroid function is recommended.

Drive and use machines

Not applicable.


levothyroxine and pregnancy

  • Levothyroxine passes very little through the placenta and its administration at appropriate doses is devoid of fetal consequences. Treatment with thyroid hormones must be continued throughout pregnancy. It is recommended to strengthen the clinical and biological surveillance especially in early pregnancy and to adapt the treatment if necessary.
  • Normal maternal thyroid function or even mild hyperthyroidism is required during pregnancy to reduce the risk of fetal hypothyroidism.
  • During pregnancy, Levothyrox should not be used with anti-thyroid medications for hyperthyroidism. Indeed, only very small amounts of Levothyrox cross the placenta, while large amounts of anti-thyroid drugs pass from mother to child. This can result in fetal hypothyroidism.

levothyroxine and feeding

  • Breastfeeding is possible in case of treatment with thyroid hormones.

levothyroxine and Fertility

  • Hypothyroidism or hyperthyroidism can affect fertility. Treatment of hypothyroidism with Levothyrox should therefore be adapted on the basis of biological monitoring since under-dosing may not improve hypothyroidism and overdose may lead to hyperthyroidism.

What should I do if I miss a dose?

Pharmacotherapeutic group: thyroid medications, ATC code: H03AA01

  • Thyroid hormone, chemically defined in its natural form L more active than form D.
  • Levothyroxine essentially increases tissue oxygen consumption, basic metabolism, heart rate.

What happens if I overdose from LEVOTHYROX ?

Acute intoxications are generally of moderate severity in the absence of cardiac history, including during accidental ingestions in children. In symptomatic cases, clinical effects may occur within a few hours or be delayed by a few days in the case of a single dose and may include one or more signs of thyrotoxicosis (see below).
In the case of repeated doses of supratherapeutic doses, the following signs of hyperthyroidism have been observed and, in the most severe cases, define a state of thyrotoxicosis:

  • Digestive disorders: vomiting, abdominal pain, diarrhea, increased appetite, weight loss.
  • Cardiovascular disorders: tachycardia, atrial fibrillation arrhythmia or extrasystoles, hypertension, chest pain, angina, congestive heart failure, cardiogenic collapse.
  • General disorders: fever, redness of the skin, sweating.
  • Neurological disorders: irritability, insomnia, headache, agitation, confusion, mydriasis, convulsions in predisposed patients, disturbances of consciousness, coma, acute psychosis.

The severity of the clinical manifestations is neither correlated with the dose ingested nor with the serum T4 and T3 determination.
Beta-sympathomimetic effects, such as tachycardia, anxiety, agitation, or hyperkinesia, may be relieved by a beta-blocker.
Exceptionally, after ingestion of a massive, life-threatening dose, plasmapheresis or haemoperfusion on charcoal may be considered.
In case of excessive doses, especially at the time of initiation of treatment, rare cases of seizures have been reported in epileptic patients.

What is Composition?

  p cp
Levothyroxine Sodium (INN) 25 μg
or 50 μg
or 75 μg
or 100 μg
or 125 μg
or 150 μg
or 175 μg
or 200 μg
  • Excipients (common): mannitol, corn starch, gelatin, croscarmellose sodium, magnesium stearate, anhydrous citric acid.

What is forms? 

The tablet can be divided into two equal half-doses.


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general information:

  • Includes a general description of the drug, its use, brand names, FAQs, and relevant news and articles

Additional information:

  • General explanation about dealing with the medicine: how to take the medicine, the doses and times of it, the start and duration of its effectiveness, the recommended diet during the period of taking the medicine, the method of storage and storage, recommendations in cases for forgetting the dose and instructions to stop taking the drug and take additional doses.

Special warnings:

  • For pregnant and breastfeeding women, the elderly, boys and drivers, and use before surgery.

Side effects:

  • It treats possible side effects and drug interactions that require attention and its effect on continuous use.
  • The information contained in this medicine is based on medical literature, but it is not a substitute for consulting a doctor.
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