Home Medicines L-thyroxine: effect, application, side effects

L-thyroxine: effect, application, side effects

by Josephine Andrews
Published: Last Updated on 355 views

L-thyroxine (levothyroxine) is an artificially produced thyroid hormone. It is mainly prescribed when the thyroid gland does not produce enough thyroxine itself, for example in the case of hypothyroidism. Properly dosed, L-thyroxine is usually very well tolerated. However, it is important to avoid interactions with certain foods or other medications. Read everything you need to know about L-thyroxine here.

How does L-thyroxine work?

The thyroid produces the hormones triiodothyronine (T3) and thyroxine (T4), which primarily regulate metabolic processes. If there is a hormone deficiency, these processes can no longer run smoothly. This leads to symptoms such as exhaustion, tiredness or depressive moods.

L-thyroxine: effect

Artificially produced L-thyroxine closes the gap if the thyroid produces too little thyroxine due to illness. During treatment, the body replenishes its thyroxine stores to release the L-thyroxine active ingredient when needed.

When is L-thyroxine used?

L-thyroxine is mainly used in the following cases:

  • in case of hypothyroidism (hypothyroidism)
  • in thyroid enlargement (goiter)
  • after thyroid surgery
  • for hyperthyroidism (hyperthyroidism) in combination with thyreostatics (thyroid blockers)

L-thyroxine for hypothyroidism

If the thyroid gland is underactive (hypothyroidism), the thyroid produces too little thyroxine (and triiodothyronine). Among other things, this can lead to tiredness, poor performance and poor concentration, depressive moods, constipation, weight gain and hair loss .

The lack of hormone production in the thyroid gland can be congenital or acquired. Hypothyroidism very often only develops in adults over the course of their lives. The reason is usually an inflammation of the organ (thyroiditis such as Hashimoto’s thyroiditis). In addition, an operation or radioiodine therapy can also be the cause of hypothyroidism.

L-thyroxine for thyroid enlargement (goiter)

An enlarged thyroid (“goiter”) is usually caused by a lack of iodine. Then the pituitary gland produces more of the hormone TSH, which stimulates the thyroid gland to grow. If left untreated, it can result in goiter.

L-thyroxine interrupts this growth process. The hormone is often prescribed together with iodine to treat iodine deficiency goiter particularly effectively. This therapy can sometimes prevent the enlarged thyroid gland from having to be surgically reduced.

L-thyroxine after thyroid surgery

If the goiter is already far advanced, often only surgery can help. The doctors remove tissue from the thyroid gland, which can then produce correspondingly less thyroxine. In order to prevent goiter from forming again, those affected must regulate their hormonal balance by taking L-thyroxine.

Sometimes it is even necessary to completely remove the thyroid gland. Then the lifelong intake of artificial thyroxine is absolutely necessary, since the body can no longer produce the important active ingredient itself.

L-thyroxine is also used after the surgical removal of a thyroid tumor. After the procedure, hormone production is often reduced, which has to be compensated for by taking L-thyroxine.

L-thyroxine for hyperthyroidism

If the thyroid gland produces too many hormones, this is referred to as an overactive thyroid gland (hyperthyroidism). Those affected suffer, for example, from restlessness, nervousness, increased blood pressure or cardiac arrhythmia. Around 90 percent of patients also develop an enlarged thyroid (goiter).

Hyperthyroidism is treated with so-called antithyroid drugs (thyroid blockers). L-thyroxine is sometimes also prescribed.

L-thyroxine for weight loss?

People with an underactive thyroid often unintentionally gain weight without changing their eating habits. L-thyroxine compensates for the lack of hormones and thus combats the symptoms of hypothyroidism, which also means weight gain.

The artificial thyroid hormone is by no means suitable as a diet! Because if there is no disease, the thyroid produces enough thyroxine itself. If L-thyroxine is then added to the body, symptoms of an overactive thyroid gland can develop, such as tachycardia, high blood pressure, restlessness and anxiety.

Never take L-thyroxine without a doctor’s recommendation. Above all, L-thyroxine is not suitable for preventing weight gain.

L-thyroxine: alternative forms of treatment?

Properly dosed, L-thyroxine is very well tolerated. Some patients are still looking for an alternative, for example because of possible interactions with other medications.

In principle, this wish should be discussed with the doctor treating you. Because alternatives to hormone replacement therapy with L-thyroxine are – if at all – only conceivable for very mild thyroid diseases. Then it is sometimes enough to take iodine tablets instead of L-thyroxine.

Naturopaths see other treatment options such as Schuessler salts or homeopathic substances. However, their effect has not been scientifically proven.

A lack of vital thyroid hormones must be treated by conventional medicine. Alternative healing methods such as homeopathy should only be used concomitantly.

How L-thyroxine is used

L-thyroxine is usually taken in tablet form, but there are also L-thyroxine drops. Discuss with your doctor which dosage form is best for you.

L-thyroxine: dosage

The optimal hormone level varies from person to person. Therefore, the necessary L-thyroxine dose is individual. The doctor treating you determines the dose and the duration of treatment.

The therapy usually starts with a low dose of L-thyroxine – 25 micrograms are usual at the beginning. If that is not enough, the dose can be increased step by step to L-thyroxine 50, 75, 100 or L-thyroxine 125 micrograms. The maximum dose is 200 micrograms per day.

Treatment with L-thyroxine requires patience from the patient because the thyroid hormone is only absorbed very slowly through the intestines. Accordingly, therapeutic successes are not immediately apparent, but only after a certain period of treatment.

During therapy, the doctor regularly checks blood values ​​to monitor the thyroxine level in the blood. In this way he can see whether the current dosage is sufficient or whether it is too high or too low and therefore needs to be adjusted. This dose adjustment phase can last up to several months. However, once those affected are properly adjusted, the symptoms usually improve quickly.

Sometimes the L-thyroxine dosage needs to be re-adjusted over time. The individual hormone requirement depends on various factors such as age or pregnancy.

L-thyroxine: ingestion

Doctors usually recommend taking L-thyroxine once a day in the morning, about 30 minutes before breakfast, on an empty stomach. Swallow the medication with water only. In particular, L-thyroxine intake with coffee or foods containing calcium such as milk or yoghurt should be avoided! Because these foods bind the active ingredient and thus delay its absorption in the intestine.

Recent study results suggest that the body can use L-thyroxine better when it is taken in the evening rather than in the morning. Taking L-thyroxine in the evening reduces typical side effects of therapy such as difficulty falling asleep, morning tiredness or inner restlessness in the morning. However, a final scientific assessment is pending.

If you forget to take the L-thyroxine, you do not have to catch up. Then simply swallow the next regular dose at the scheduled time, according to your treatment plan.

Discontinue L-Thryroxine

Patients with an underactive thyroid gland or goiter usually have to take L-thyroxine for the rest of their lives. Because if you stop or taper L-thyroxine (i.e. reduce the dose slowly), the symptoms of the underlying thyroid disease return over time.

This also applies to thyroid inflammation: stopping L-thyroxine is usually not an option with Hashimoto’s thyroiditis. Because the autoimmune disease destroys thyroid tissue in batches and irretrievably. The remaining tissue can only produce L-thyroxine to a limited extent, so that the hormone has to be supplied continuously.

Discontinuing L-thyroxine can be dangerous. Therefore, you should never stop treatment with L-thyroxine or reduce your dose on your own, but always talk to your doctor first!

What are the side effects of L-thyroxine?

Once the dosage is set correctly, L-thyroxine is usually well tolerated. However, as with any drug, side effects can occur with L-thyroxine, especially in the early stages of therapy. Examples of possible side effects include:

  • palpitations/palpitations
  • insomnia
  • headache
  • Nervousness, inner restlessness
  • increased intracranial pressure (mainly in children)
  • cardiac arrhythmias
  • increased sweating
  • skin rash
  • muscle weakness
  • Gastrointestinal complaints
  • Tremble
  • menstrual cramps
  • weight loss

Another side effect of L-thyroxine affects women going through menopause: L-thyroxine increases their risk of osteoporosis. L-thyroxine can also cause water retention. However, this happens relatively rarely.

L-thyroxine: overdose

If L-thyroxine is dosed too high, there are side effects. The typical symptoms of an overactive thyroid usually appear then, such as tachycardia, high blood pressure, diarrhoea, vomiting and/or abdominal pain, anxiety and restlessness, heavy sweating or fever.

In the event of an acute, significant overdose of L-thyroxine, you should observe the following recommendations:

  • do not force vomiting
  • don’t drink water
  • Contact poison control center, hospital ambulance or attending physician

L-thyroxine: underdosing

The right dosage depends, among other things, on the type and severity of the thyroid disease to be treated, on the absorption capacity of the intestine and possible interactions with other substances. Against this background, an underdose can occur, especially at the beginning of L-thyroxine therapy, as the doctor approaches the right dose step by step.

If the L-thyroxine is underdosed, the symptoms of thyroxine deficiency such as tiredness and exhaustion remain at least in a weakened form.

If you notice that your symptoms do not (completely) disappear despite taking L-thyroxine, you should tell your doctor. He will then increase the dose if necessary.

When not to take L-thyroxine?

Patients who are allergic to the active ingredient should not use L-thyroxine. Other contraindications are:

  • untreated hyperthyroidism or adrenal insufficiency
  • acute myocardial infarction, acute myocarditis, acute heart wall inflammation (pancarditis)
  • untreated dysfunction of the pituitary gland

Pregnant women can and must continue to take prescribed L-thyroxine. However, the dose may need to be adjusted as hormone requirements may increase during pregnancy. It is not permitted to take L-thyroxine and thyroid blockers at the same time during pregnancy.

L-Thyroxine: Interactions

Certain medications can affect how L-thyroxine works, including:

  • Phenytoin (medicine for epilepsy , cardiac arrhythmia and nerve pain)
  • Salicylates (painkillers and fever relievers)
  • Dicoumarol (anticoagulant)
  • Furosemide (dehydrating agent = diuretic)
  • Sertraline (antidepressant)
  • Chloroquine and proguanil (antimalarials)
  • Barbiturates (sleeping pills and tranquilizers)
  • amiodarone (anti-arrhythmic medicine)

In addition, the pill can increase the need for L-thyroxine.

Certain foods and dietary supplements also influence the effect by delaying the absorption of L-thyroxine from the intestine. This applies in particular to milk, foods containing soy, high-fat foods, calcium and iron supplements and antacids (acid binders, for example against heartburn).

Conversely, L-thyroxine can slow down the effects of other medications. For example, the artificial hormone can:

  • reduce the blood sugar lowering effect of metformin , insulin or glibenclamide
  • increase the anticoagulant effect of certain medications such as phenprocoumon

By the way: Some people worry about a possible interaction between L-thyroxine and vitamin D – presumably because hypothyroidism is often associated with vitamin D deficiency. Then it may be advisable to take vitamin D supplements in addition to L-thyroxine. This is not usually a problem as the two active ingredients do not seem to affect each other.

As a general rule, discuss the concomitant use of L-thyroxine and other medications or dietary supplements with a doctor or pharmacist first.

Where can you get medicines with L-thyroxine?

L-thyroxine supplements require a prescription. You can get the medicines from the pharmacy on presentation of a doctor’s prescription.

Since when is L-thyroxine known?

On Christmas Eve 1914, the researcher Edward C. Kendall succeeded for the first time in isolating the thyroid hormones he had been looking for for a long time. This laid the foundation for the artificial production of thyroxine – in the form of L-thyroxine.

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