Levothyroxine (Oral)

Prescribed to patients with an underactive thyroid, Levothyroxine is used to supplement the body’s natural production of thyroid hormones and to treat the symptoms of hypothyroidism.


Situated in the neck, the thyroid gland is responsible for producing certain hormones which control the patient's metabolism. If the thyroid produces too few hormones, it is deemed to be underactive, whereas an overactive thyroid produces an excess of thyroid hormones.

Patients with an underactive thyroid are diagnosed with hypothyroidism. Whilst some medications and surgeries can damage the thyroid gland and cause hypothyroidism, the condition can also occur when the patient's immune system attacks the thyroid gland and prevents it from producing the appropriate amount of hormones.

Common symptoms of hypothyroidism are fatigue, breathlessness weight gain, dizziness, depression, loss of appetite and constipation, but patients may experience more severe symptoms if their hormone levels drop to an exceptionally low level. Often referred to as decompensated hypothyroid or a myxedema coma, patients with extremely low levels of thyroid hormones require emergency medical treatment.

As Levothyroxine is a synthetic form of naturally produced thyroxine, it can be used to supplement the patient's natural thyroid hormones. Whilst Levothyroxine won't cure hypothyroidism, it can be used on a long-term basis to increase the patient's hormone levels and prevent the symptoms of hypothyroidism occurring.

If patients are suspected of having an underactive thyroid, blood tests can be carried out to confirm the diagnosis. By testing the patient's thyroxine and thyroid-stimulating hormone (TSH) levels, physicians can determine whether the thyroid is functioning correctly. If hypothyroidism is confirmed, Levothyroxine can be prescribed to increase the patient's hormone levels.

Depending on the severity of the patient's condition, various doses of Levothyroxine can be prescribed. Often, the patient will be given a relatively low starting dose of Levothyroxine and further tests will be carried out in order to determine what effect the medication is having. If the patient's test results indicate that their thyroid is still underactive, their dose of Levothyroxine may be increased.

Whilst Levothyroxine can be used to successfully treat hypothyroidism, it is important that patients have regular blood tests to establish what their hormone levels are whilst they are receiving treatment. If patients take too much Levothyroxine or take the medication too often, they may have an excess of thyroid hormones, which could lead to hyperthyroidism.

By prescribing an appropriate amount of Levothyroxine and modifying the patient's dose as required, physicians can successfully treat patients with an underactive thyroid and ensure that their hormone levels stay within an appropriate range.

Conditions Treated

Hypothyroidism (Underactive thyroid)

Type Of Medicine

Synthetic thyroid hormone

Side Effects

Any type of medication can cause patients to experience adverse effects but some side effects may be more serious than others. Often, patients will develop relatively mild side effects when they first start using a new medication but these will reduce over time.

When patients are taking Levothyroxine, for example, they may experience the following side effects:

  • Stomach or abdominal cramps
  • Hair loss
  • Change in appetite
  • Feeling of distrust and suspicion
  • Crying
  • Nervousness
  • Diarrhea
  • Unusual or false sense of well-being
  • Increased appetite
  • Fear
  • Muscle weakness
  • Feeling unhappy or not well
  • Mental depression
  • Feeling of discomfort
  • Unusual weakness or tiredness
  • Headache
  • Trouble sitting still
  • Feeling of warmth
  • Quick to react or overreact emotionally
  • Feeling things are not real
  • Rapidly changing moods
  • Weight gain
  • Redness of the arms, neck, face, neck and, sometimes, upper chest
  • Vomiting
  • Restlessness
  • Weight loss
  • Trouble getting pregnant

If the above side effects are not bothersome to the patient and decrease over time, medical intervention may not be required. However, if the side effects persist or are severe, patients should obtain medical advice.

When taking Levothyroxine, patients should notify their doctor immediately if they develop any of the following side effects:

  • Chest discomfort or pain
  • Nausea
  • Decreased urine output
  • Heat intolerance
  • Labored or difficult breathing
  • Increased blood pressure
  • Difficulty with swallowing
  • Increased pulse
  • Dilated neck veins
  • Irregular breathing
  • Extreme fatigue
  • Welts or hives
  • Fainting
  • Irregular, slow, pounding, racing or fast pulse or heartbeat
  • Fever
  • Discomfort or pain in the haw, arms, neck or back
  • Irritability
  • Severe headache
  • Tremors
  • Menstrual changes
  • Shortness of breath
  • Eye pain
  • Skin redness, rash or itching
  • Pain in the knee or hip
  • Sweating
  • Lack or slowing of normal growth in children
  • Swelling of the lips, throat, face, tongue or eyes
  • Blurred vision
  • Tightness in the chest
  • Double vision
  • Troubled breathing
  • Dizziness
  • Limp or walk favoring one leg
  • Seizures

Patients should also access medical advice if they experience any side effects which are not listed above when taking Levothyroxine.

If patients take too much Levothyroxine or if they take the medication too often, they may exhibit symptoms of an overdose. If so, the patient will require emergency medical treatment. The symptoms of a Levothyroxine overdose may include:

  • Change in consciousness
  • Sudden headache
  • Clammy, cold skin
  • Weak or fast pulse
  • Confusion
  • Lightheadedness
  • Disorientation
  • Sudden loss of coordination
  • Loss of consciousness
  • Sudden slurring of speech

If patients are aware that they've taken too much Levothyroxine, they should seek medical help straight away and should not wait until the symptoms of an overdose start to occur.


Once patients have been diagnosed with hypothyroidism, their physician will prescribe them with Levothyroxine. However, the patient's dose will depend on numerous factors, such as their age, weight, medical history, symptoms and blood test results.

Generally, the patient's dose will be dependent on their weight. If adults and teenagers are prescribed Levothyroxine tablets or capsules for the treatment of hypothyroidism, for example, they are usually advised to take 1.7mcg per kilogram of bodyweight per day.

For pediatric patients over the age of twelve years, the typical dose of Levothyroxine tablets or capsules is 2-3mcg per kilogram of bodyweight per day. Whilst patients between the ages of six to twelve years may be instructed to take 4-5mcg per kilogram of bodyweight per day, in tablet or capsule form.

If patients under the age of six years are prescribed Levothyroxine for the treatment of hypothyroidism, they will usually be prescribed the medication in tablet form or as an oral suspension. Patients under the age of six years are not usually prescribed capsules as they may present a choking hazard if the patient is unable to swallow them.

Patients between the ages of one and five years are generally prescribed Levothyroxine at a rate of 5-6mcg per kilogram of bodyweight per day, whilst patients aged between six and twelve months are usually given 6-8mcg per kilogram of bodyweight. If necessary, younger patients can also be prescribed Levothyroxine if they are diagnosed with an underactive thyroid. Infants between the ages of three and six months are usually prescribed 8-10mcg per kilogram of bodyweight per day, whereas infants under the age of three months are usually given 10-15mcg per kilogram of bodyweight per day.

In some cases, Levothyroxine can also be used to treat thyroid cancer. When patients are prescribed Levothyroxine for this purpose, their dose can vary but is usually more than 2mcg per kilogram of bodyweight per day.

Although this is a standard dosing regime for treatment with Levothyroxine, every patient is assessed individually and patients should always follow their doctor's instructions when taking this medication. Patients should not alter their dose or stop taking Levothyroxine unless they are advised to do so by a medical professional.

In most cases, patients are instructed to take Levothyroxine on an empty stomach. Generally, patients are advised to take their medication in the morning, at least 30-60 minutes before eating breakfast.

If patients are taking antacids, cholestyramine, calcium supplements, sucralfate, iron supplements, simethicone and/or orlistat, Levothyroxine should be taken at least four hours before or four hours after these medicines have been taken.

Similarly, some foods can affect the absorption of Levothyroxine. Patients should not consume walnuts, dietary fiber, cotton seed meal and/or soybean flour (which may be present in infant formula) at the same time as taking their medication. If patients are not able to cut these products out of their diet, they should discuss this with their doctor and determine when they can safely consume these items whilst taking Levothyroxine.

If patients are prescribed Levothyroxine in capsule form, they should swallow the capsule whole and should not attempt to open it, break it or crush it. If tablets are prescribed, the tablet can be swallowed whole or crushed and mixed with 5-10 milliliters of water. The mixture should be administered straight away and can be given to the patient using a dropper or a spoon.

In order for Levothyroxine to be effective, it should be taken in accordance with the patient's treatment schedule. If the patient forgets to take a dose of Levothyroxine, they should take it as soon as they remember to do so. However, if their next dose is due soon, patients should skip the missed dose and continue to take their medication as they normally would. Patients should not take an extra dose of Levothyroxine, even if an earlier dose has been missed.

If patients are unsure how to take Levothyroxine or when to take it, they should contact their physician or pharmacist for advice.

Potential Drug Interactions

As some medicines can interact with each other, it may not be appropriate for certain drugs to be used at the same time. If patients are taking Levothyroxine, for example, the use of the following medications is not recommended:

  • Amineptine
  • Mirtazapine
  • Amitriptyline
  • Maprotiline
  • Amitriptylinoxide
  • Nortriptyline
  • Amoxapine
  • Opipramol
  • Clomipramine
  • Desipramine
  • Ketamine
  • Dibenzepin
  • Melitracen
  • Doxepin
  • Tianeptine
  • Imipramine
  • Protriptyline
  • Lofepramine
  • Trimipramine

In some cases, however, it may be necessary to treat the patient with Levothyroxine and one of the medications listed above. If so, the patient may be prescribed a modified dose of medication or instructed to take their medicine at a specific time.

Additionally, if Levothyroxine is taken alongside any of the following medicines, patients may have an increased risk of developing side effects:

  • Acenocoumarol
  • Patiromer
  • Aluminum Carbonate, Basic
  • Phenindione
  • Aluminum Hydroxide
  • Phenprocoumon
  • Estropipate
  • Aluminum Phosphate
  • Phenytoin
  • Estrone
  • Anisindione
  • Calcium Acetate
  • Omeprazole
  • Calcium Carbonate
  • Rifapentine
  • Calcium Citrate
  • Pantoprazole
  • Cholestyramine
  • Rifampin
  • Chromium
  • Rabeprazole
  • Ciprofloxacin
  • Kelp
  • Colesevelam
  • Lansoprazole
  • Conjugated Estrogens
  • Lanthanum Carbonate
  • Dexlansoprazole
  • Iron
  • Dicumarol
  • Lopinavir
  • Dihydroxyaluminum Aminoacetate
  • Magaldrate
  • Dihydroxyaluminum Sodium Carbonate
  • Ritonavir
  • Eltrombopag
  • Magnesium Trisilicate
  • Esomeprazole
  • Magnesium Oxide
  • Esterified Estrogens
  • Magnesium Carbonate
  • Estradiol
  • Magnesium Hydroxide
  • Estriol
  • Sevelamer
  • Imatinib
  • Simvastatin
  • Fosphenytoin
  • Warfarin

As well as interacting with some medicines, Levothyroxine can also interact with other substances. If patients consume the following when taking Levothyroxine, for example, they may experience increased side effects:

  • Soybeans
  • Enteral nutrition

Before using Levothyroxine, patients should tell their physician if they are using any other medicines, including over-the-counter medications, supplements or vitamins. Similarly, patients should obtain medical advice before using any new medicines, vitamins or supplements once they have started taking Levothyroxine.


If patients have any existing medical conditions, they must inform their physician before they start taking Levothyroxine. There are some conditions which could affect the use of Levothyroxine and these may include:

  • Osteoporosis
  • Heart rhythm problems
  • Pituitary gland problems
  • Adrenal gland insufficiency
  • Thyrotoxicosis
  • Heart attack
  • Blood clotting problems
  • Anemia, particularly pernicious anemia
  • Adrenal problems
  • Angina
  • Diabetes
  • Blood vessel or heart disease
  • Inability to swallow capsules

Although Levothyroxine can be prescribed to geriatric patients, older people may be more likely to have age-related blood vessel or heart problems and this could affect their use of Levothyroxine. In some cases, geriatric patients should be given a modified dose of Levothyroxine.

When patients are taking Levothyroxine, they should have regular blood tests and regular check-ups with their physician. This enables doctors to confirm that the patient is taking an appropriate dose of Levothyroxine and that the medication is not having any unwanted effects.

Levothyroxine should not be taken for the purposes of losing weight. Taken in normal doses, Levothyroxine will not promote weight loss and, if taken in high doses, the medication may cause serious health problems.

If diabetic patients are diagnosed with an underactive thyroid, they may be prescribed Levothyroxine. However, diabetic patients taking Levothyroxine will need to check their blood and/or urine sugar levels regularly. Patients should be told how often to check their blood sugar levels by their doctor. If patients notice any changes in their sugar levels, they should notify their physician straight away.

Female patients who take Levothyroxine for a long period of time may have an increased risk of bone loss and osteoporosis. If patients are concerned about this risk, they should contact their physician.

If patients experience any of the following symptoms, it may indicate that too much Levothyroxine is in their system and urgent medical treatment must be obtained:

  • Heat intolerance
  • Rash on the skin
  • Hives
  • Changes in menstrual periods
  • Fever
  • Excessive sweating
  • Diarrhea
  • Vomiting
  • Change in appetite
  • Weight loss or gain
  • Tremors
  • Sleeplessness
  • Irritability
  • Leg cramps
  • Shortness of breath
  • Nervousness
  • Headaches
  • Chest pain
  • Irregular or rapid heartbeats

If patients consult with any doctors, dentists or other healthcare practitioners, they should inform them that they are taking Levothyroxine. If patients are due to undergo any medical procedures or tests, they may be advised to stop using Levothyroxine in advance.

However, patients should not alter their dose of Levothyroxine or stop taking their medication unless they are advised to do so. Doing so could increase the risk of experiencing side effects. If patients are advised to discontinue treatment with Levothyroxine, they may be instructed to lower their dose of medication gradually before stopping treatment completely.

When patients first start using Levothyroxine, they may experience a temporary loss of hair. In some cases, this could continue throughout the first few months of treatment. If patients are concerned about this side effect or if the hair loss persists, they should contact their physician for advice.

In some cases, hypothyroidism can cause infertility in both male and female patients. When taking Levothyroxine, these infertility problems may be resolved. However, Levothyroxine should not be used to treat infertility unless it is caused by hypothyroidism.

As a category A medicine in relation to pregnancy, Levothyroxine is thought to pose a minimal risk to pregnant patients and their unborn baby. However, patients should notify their physician immediately if they become pregnant when taking this medication. In some cases, patients may need to take a higher dose of Levothyroxine when they are pregnant.

To date, studies have shown that Levothyroxine presents a minimal risk if it is taken whilst breastfeeding. However, patients should obtain medical advice before breastfeeding whilst taking Levothyroxine, or any other medication.

If patients have any allergies, they should inform their physician before they start taking Levothyroxine. This includes allergies to other medicines, foods, preservatives, dyes and/or animals. In rare cases, patients may exhibit an allergic response when taking Levothyroxine. As a serious allergic reaction can be life-threatening, patients will need to obtain emergency medical treatment if they develop a reaction when taking Levothyroxine. The symptoms of an allergic reaction may include:

  • Difficulty swallowing
  • Difficulty breathing
  • Itching
  • Hoarseness
  • Hives
  • Rash on the skin
  • Shortness of breath
  • Wheezing
  • Swelling of the lips, tongue, throat, mouth, face or hands


As patients are usually advised to take Levothyroxine on a daily basis, they will need to keep a supply of this medication at home. When storing medicines in the home, the patient should ensure that they are kept in a safe location. It is particularly important that children and/or pets cannot access Levothyroxine or any other medication.

To store Levothyroxine properly, patients should follow the manufacturer's instructions and medication guidelines. In most cases, Levothyroxine can be kept at room temperature but should be kept in a closed container at all times. Levothyroxine also needs to be kept away from moisture, heat and direct light.

If patients are advised to stop taking Levothyroxine or if the medicine reaches its expiration date, patients should dispose of it responsibly. Medication should not be thrown out with regular household waste as it may pose a risk to other people. To dispose of Levothyroxine, patients should contact their physician's office or pharmacist and make use of a specialist medicine disposal service.


In most cases, hypothyroidism is a life-long condition and patients will be required to take medication for the remainder of their life once they have been diagnosed with an underactive thyroid. However, the condition can be treated fairly easily with Levothyroxine and patients should notice a reduction in their symptoms once the medication begins to take effect.

Although serious complications arising from hypothyroidism are fairly rare, they can occur. If patients have extremely low levels of thyroid hormones, for example, they could fall into a myxedema coma state. Characterized by mental confusion, low body temperature, low blood sugar and low blood pressure, a myxedema coma can be fatal if left untreated. With swift treatment, however, patients often go on to make a full recovery, even if they have experienced extremely low hormone levels.

For most patients, hypothyroidism is well-controlled via a daily dose of Levothyroxine. Whilst the medication can take a number of weeks to become fully effective, patients should obtain relief from their symptoms when using Levothyroxine and should also reduce their risk of developing complications arising from hypothyroidism.