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February 23, 2023 13 min read

Levothyroxine is a medication commonly prescribed for people who have hypothyroidism. It's an important drug that helps to balance thyroid hormones in the body, but how much do we really know about it? If you are considering taking levothyroxine or have been prescribed this medication, it's essential to understand what it does, how it works, the side effects, and the proper way to take it. So, here's everything you need to know about levothyroxine.

What is levothyroxine?

Levothyroxine is a synthetic form of T4, which is a hormone produced by the thyroid gland. Although it's manmade, it's exactly like the natural T4 hormone that your thyroid makes. It's prescribed as a thyroid hormone replacement medication for people with hypothyroidism, a condition where the thyroid doesn't produce enough thyroid hormone.

Levothyroxine is the standard treatment for hypothyroidism, according to the American Thyroid Association. Therefore, if you've just been diagnosed with the condition, your doctor will likely prescribe it. This medication is so widely used that it's among the most commonly prescribed drugs worldwide.

There are various forms of levothyroxine, including tablets, capsules, and liquids that you swallow. It also comes in an injectable solution form that's only administered by a healthcare provider.

Some of the brand names of levothyroxine tablets are Synthroid, Levoxyl, Unithroid, and Tirosint-Sol. Generic versions of levothyroxine are also available and are typically less expensive than the brand-name versions.

Levothyroxine tablets are available from 25 micrograms (mcg) to 300 mcg. Each strength has a different color. Liquid levothyroxine is available from 13 micrograms per milliliter (mcg/ml) to 200 mcg/ml.

What is levothyroxine used for?

Levothyroxine is a medication used to treat underactive thyroid, which is a condition where the thyroid gland doesn't produce enough thyroid hormone. This can be caused by various factors, including Hashimoto's thyroiditis and surgical removal of the thyroid. The thyroid hormone is important because it regulates metabolism, heart rate, and body temperature. When there's not enough of it, it can result in a wide range of symptoms, such as fatigue, weight gain, depression, increased sensitivity to colds, and constipation.

Fortunately, levothyroxine is an effective treatment that can help reverse these symptoms. When taken correctly, it can help regulate thyroid hormone levels and restore normal function in the body.

Although levothyroxine can control the symptoms of hypothyroidism, it can't cure the condition. This means that most patients will need to continue taking hormone replacement medication for the rest of their lives.

In addition to treating hypothyroidism, levothyroxine is also used to treat other conditions such as thyroid cancer, shrink goiter, or an enlarged thyroid gland and to treat hypothyroidism after thyroidectomy or radiation therapy.

Everything you need to know about levothyroxine

How does levothyroxine works?

Levothyroxine is a medication that belongs to a group of drugs called hormones. It works by replacing the missing thyroid hormones and restores normal levels in people with hypothyroidism, thereby relieving symptoms associated with the condition. In other words, it provides the thyroid hormone that your thyroid would produce if it were working normally.

The thyroid produces two main hormones: thyroxine (T4) and triiodothyronine (T3). T4 is inactive and needs to be converted to T3, the active form. When you take levothyroxine, your body converts it to T3, just like how your body converts natural T4 to T3.

What are the benefits of levothyroxine?

There are various benefits of levothyroxine. These include:

  • Levothyroxine replaces the missing thyroid hormone in people with low thyroid function or hypothyroidism. Thus, it can provide you with relief from hypothyroidism symptoms, such as fatigue, weight gain, slow heartbeat, and low energy levels.

  • Levothyroxine therapy works for children with congenital hypothyroidism, which is hypothyroidism in newborns that can cause severe intellectual and physical disabilities if left untreated. The medication rapidly restores thyroid hormone levels to normal.

  • People with hypothyroidism from any cause can take levothyroxine, except for subacute thyroiditis, which is a temporary swelling and inflammation of the thyroid caused by a virus.

  • Levothyroxine is approved for thyroid stimulating hormone (TSH) suppression, as an adjunct to surgery, and radioactive iodine therapy to control cancer of the thyroid and treat certain types of goiter.

  • Levothyroxine is available in generic drug forms, which are cheaper than brand-name medicines and easily found in pharmacies.

What are the drawbacks of levothyroxine?

While levothyroxine offers a lot of benefits, there are also some drawbacks you need to be aware of. These include:

  • Some of the inactive ingredients of levothyroxine may cause allergic reactions in patients who are sensitive to them.

  • This synthetic T4 may interact with other medications like proton pump inhibitors or some foods like dietary fiber, which leads to decreased levothyroxine absorption.

  • You need to take your levothyroxine dosage on an empty stomach.

  • Levothyroxine is not effective immediately.

  • Taking too much levothyroxine can lead to hyperthyroidism or an overactive thyroid, but a too low dose of it means it's ineffective.

  • You may experience temporary hair loss when you have just started taking levothyroxine.

  • Long-term use of levothyroxine may decrease bone mineral density, increasing osteoporosis and fracture risk.

  • The dose of levothyroxine is affected by other medical conditions such as diabetes, blood clotting disorders, or pregnancy.

How do doctors determine your dosage?

Achieving the benefits of levothyroxine while avoiding potential side effects all boils down to finding the right dosage. Your doctor will determine your appropriate Levothyroxine dose by first ordering thyroid function tests.

The first test is known as the TSH test, which measures the levels of thyroid-stimulating hormone (TSH) in your body. TSH is a hormone produced by your pituitary gland that regulates your thyroid hormone production and release. When your thyroid hormone levels are too low, your pituitary gland will release more TSH. Thus, a high level of TSH indicates hypothyroidism.

Aside from your test results, your doctor will also determine your dose based on your weight, age, and other medical condition you may have. Furthermore, the levothyroxine dose may vary depending on the intended use of the medication. For instance, the dose might be higher if it's used for THS suppression.

In general, your doctor will start with a lower dose and adjust it over time based on changes in weight, height, age, serum TSH, or other health problems.

Dosage for hypothyroidism

For adults with hypothyroidism, a typical starting dose is 12.5 to 25 mcg, which can be increased periodically every 4 to 6 weeks up to a maximum of 200 mcg per day. The dosage for elderly individuals or those with underlying heart disease typically starts lower, usually from 12.5 mcg per day, and increases gradually every 6 to 8 weeks.

Children's dosage is determined by their age and body weight. Children older than 12 years of age typically receive a daily dose of 2 to 3 mcg per kg of body weight, while those between 6 and 12 years of age typically receive 4 to 5 mcg per kg of body weight per day. However, levothyroxine tablets and capsules use is not recommended for children younger than six years old, as they may find them difficult to swallow.

People with mild hypothyroidism (TSH < 10 mU/L) may require very low doses, as little as 1 mcg/kg/day.

Dosage for goiter

To treat goiter, it's recommended to take a daily dose of 50-200 micrograms. Studies have shown that taking 150 mcg per day can decrease the size of the goiter by about 20% after 3 months.

However, it's important to note that levothyroxine should not be used to suppress non-toxic diffuse goiter or benign thyroid nodules in people with enough iodine in their diet. There's no benefit to the patient in doing so, and over-treatment can lead to hyperthyroidism.

Dosage to treat thyroid cancer

Levothyroxine can be used to help control and prevent the recurrence of thyroid cancer by suppressing levels of TSH. Generally, adults are prescribed doses greater than 2 mcg per kilogram of body weight per day. However, in some cases, such as when there is a dangerous tumor present, the target level at which your TSH should be suppressed may be lower.

How and when should you take levothyroxine?

To get the best results from levothyroxine, there are a few things to keep in mind. Taking the medication on an empty stomach, either an hour before or three hours after eating is important for optimal absorption. It's common to take the medication in the morning before breakfast, but you can also take it at night before bed if that works better for you. Be sure to take levothyroxine with a full glass of water and swallow the capsule whole without cutting or crushing it. Avoid taking it with any other liquid besides water.

Consistency is key with levothyroxine. Take the exact dose prescribed by your doctor at the same time each day. Regular blood tests will help your doctor adjust your dose if needed. If you experience any unusual symptoms like hand tremors, headaches, or shortness of breath, be sure to tell your doctor.

It's important to inform your doctor or pharmacist if you are pregnant, recently received radiation therapy, or are being treated for other conditions like adrenal insufficiency, as you may need to adjust your dose of levothyroxine. It's also important to let them know about any other medications or dietary supplements you are taking or plan to take with levothyroxine sodium.

What to do if you forget to take levothyroxine

If you forget to take your scheduled dose of levothyroxine, it's important not to panic. Simply take the missed dose as soon as you remember. However, if it's already close to the time for your next dose, it's better to skip the missed dose and resume taking medicine according to your normal schedule.

It's worth noting that this synthetic T4 has a long half-life of about 6 to 7 days. Therefore, missing a few doses by accident usually doesn't result in any serious adverse effects. However, it is important to take the full prescribed dose each day to ensure that your condition is managed properly.

What to do if you take too much

It is important to never take more than the prescribed dose of levothyroxine. If you accidentally take too much, contact your doctor or emergency services right away. Overdose can cause mild to serious side effects, and can cause potential complications such as heart disease, decreased bone mineral density, or fertility problems. Serious side effects can include difficulty breathing, shock, or convulsions.

Is regular blood test important?

Regular blood tests are important for individuals with permanent hypothyroidism who rely on thyroid medication for life. These tests help doctors monitor the levels of thyroid-stimulating hormone (TSH) and adjust the medication dosage accordingly. Factors such as weight, age, overall health, and medical condition can affect the optimal dosage of thyroid medication needed. Regular blood tests can also help detect any potential complications, such as overmedication or under medication, and address them promptly to ensure that the individual's thyroid function remains stable. Therefore, it is essential to follow the recommended schedule of blood tests and keep in close communication with your healthcare provider.

What are the side effects of levothyroxine?

Like all kinds of medications, levothyroxine may cause side effects. Some of these effects may be symptoms of hyperthyroidism, indicating that the dose is too high, while others may be symptoms of hypothyroidism, indicating that the dose is too low.

Common side effects of levothyroxine

Common side effects of overdose include:

  • Shortness of breath

  • Sweat a lot

  • Sensitive to heat

  • Heart beat fast

  • Sleep problems

  • Unexplainable weight loss

  • Anxiety and discomfort

  • Mood swings

  • Diarrhea

  • Hair loss

Common side effects of a too-low dose include:

  • Cramp

  • Cold intolerance

  • Constipation

  • Tired

  • Thinking and moving slowly

  • Hair loss

  • Dry skin

  • Weight gain

  • Hoarseness

  • Puffy face

If the above symptoms persist and don't go away on their own, be sure to talk to your doctor or pharmacist. They'll likely adjust your dose.

Adverse side effects of levothyroxine

Taking too much or too little levothyroxine can also cause severe side effects. If you experience the following side effects, be sure to talk to your doctor right away.

Severe side effects of an overdose include:

  • Hand tremors

  • Headache

  • Disorientation or loss of consciousness

  • Atrial fibrillation, which is a dangerous arrhythmia

  • Blood clotting

  • Stroke

  • Heart attack, heart failure, or other heart conditions

  • Osteoporosis

  • Muscle weakness or pain

  • Irregular menstruation

  • Infertility or fertility problems

  • Dangerous complications during pregnancy, such as high blood pressure, miscarriage, and premature birth.

Severe side effects of a very low dose include:

  • Mental retardation and delayed puberty in children

  • Chest pain

  • Depression

  • Confusion

  • Anemia

  • Myxoedema coma, which is severe hypothyroidism.

Serious allergic reaction to levothyroxine

Some individuals may be sensitive to certain ingredients in the medication, leading to allergic reactions or other unpleasant responses, such as:

  • Urticaria

  • Skin rash

  • Itchy

  • Angioedema

  • Flushing

  • Fever

  • Serum sickness

  • Wheeze

  • Arthralgia

  • Digestive problems such as abdominal pain, stomach pain, nausea, diarrhea, etc.

Although allergic reactions are less frequently reported, they can be life-threatening. Thus, tell your doctor immediately if you have any of these signs of an allergic reaction. More importantly, you should seek immediate medical attention if you experience anaphylaxis, a dangerous allergy.

What other drugs interact with levothyroxine?

Levothyroxine has been found to interact with 202 other medications. These drug interactions can limit the absorption of thyroid medication, affect the conversion of T4 to T3, or interfere with your thyroid function test results. It's important to be aware of these interactions and inform your doctor if you are taking any of these medications.

Some of the common medications that interact with levothyroxine include:

  • Medicines containing iron, aluminum, calcium, and magnesium

  • Stomach medicine such as Omeprazole, Esomeprazole, and Prevacid

  • Birth control pills that contain Estrogen

  • Insulin or diabetes medications

  • Antidepressants such as amitriptyline or maprotiline

  • Oral anticoagulants

  • Non-steroidal anti-inflammatory drugs

If you are taking any of these medications or others, you should let your doctor know so that they can adjust your dosage accordingly.

Can pregnant women and breastfeeding mothers take levothyroxine?

Many women with hypothyroidism question whether thyroid hormone replacement medicine is safe during pregnancy and breastfeeding. The answer is yes; pregnant women and breastfeeding mothers can take levothyroxine. Let's discuss this in more detail.

Levothyroxine and Pregnancy

Levothyroxine is considered safe for use in pregnant women and does not increase the risk of miscarriage, birth defects, or other negative outcomes. In fact, this medication can be essential in maintaining the health of both the mother and fetus. Therefore, it's important for pregnant women with hypothyroidism to continue taking levothyroxine as prescribed and to attend all scheduled doctor appointments to ensure the health of both mother and baby.

This is because untreated hypothyroidism during pregnancy can have serious consequences. It can increase the risk of miscarriage, stillbirth, or preterm birth, and it can also negatively impact the cognitive development of the fetus.

During pregnancy, your body's need for thyroid hormones often increases, so doctors will monitor and adjust the levothyroxine dosage accordingly. After giving birth, your dosage can return to the pre-pregnancy level.

Levothyroxine and breastfeeding

Levothyroxine is generally considered safe to use while breastfeeding, as it rarely passes into breast milk in significant amounts. This means that it is unlikely to affect the development of a nursing infant's thyroid or pituitary glands.

Studies have shown that the levels of thyroid hormone in the blood of breastfed infants and bottle-fed infants are not significantly different.

Moreover, having enough thyroid hormone is important for breastfeeding. Therefore, taking this medication may be beneficial for mothers who experience delayed or insufficient milk production as a result of hypothyroidism, as it can help improve milk production.

Who needs to avoid levothyroxine?

Levothyroxine is not a suitable treatment for obesity or weight loss in individuals with or without thyroid disorders. This is due to two main reasons. Levothyroxine has been shown to be ineffective in aiding weight loss in those who have gained weight as a result of unhealthy habits, diet, or other medical conditions. Thus, it shouldn't be used to treat obesity.

Levothyroxine does aid in weight loss in those who gain weight due to hypothyroidism. This makes people think that increasing their dose will result in more weight loss. However, this isn't true and may even be dangerous. Taking high doses of this medication can lead to side effects that mimic those of hyperthyroidism, especially in people who don't have hypothyroidism. The side effects may include rapid weight loss, shortness of breath, arrhythmia, excessive sweating, and confusion. Long-term use can also lead to heart failure or osteoporosis.

In individuals with hypothyroidism, levothyroxine can help to restore fertility and increase the chances of conceiving. However, it shouldn't be used as a treatment for infertility caused by other conditions as it can lead to hyperthyroidism, which can be life-threatening.

It is also important to note that levothyroxine should not be used in individuals with untreated adrenal insufficiency as it can promote acute adrenal insufficiency.

How should you store levothyroxine?

The effectiveness of thyroid medication can be affected by temperature and humidity. Thus, it is important to store levothyroxine in a dry place or where the temperature is below 25 degrees Celsius. Direct exposure to light should also be avoided, and the medication should not be stored in damp areas such as the bathroom or sink. The American Thyroid Association (ATA) also advises patients to keep the medication away from children.

How soon can you feel the benefits of levothyroxine?

Levothyroxine typically takes time to show its effects. So if you have recently started taking the medication, it's important to be patient and allow some time for it to take effect. The length of time it takes to notice a difference will differ for each person, but on average, it takes about 4 to 6 weeks.

What if levothyroxine doesn't work for you?

Every problem has root causes. Perhaps, you have been taking levothyroxine the wrong way, so it doesn't work for you. For example, you don't take it on an empty stomach, which can impair the medication's absorption. But if you've been taking the medication the right way as recommended by your doctor or pharmacist and you've adjusted your dose several times, then it might be time you switch your medication.

Levothyroxine may not work for you if your body is unable to convert T4 to T3 effectively. In such cases, natural desiccated thyroid (NDT) can be a good alternative. Unlike levothyroxine, which only contains T4, NDT contains both T4 and T3 thyroid hormones. This means your body can use it immediately without the need for conversion. In fact, studies have shown that NDT is preferred since it offers better relief from symptoms. Plus, NDT is popular among those who want a more natural approach to their treatment since it's made of pig thyroid glands.

If you want to try NDT, you may want to consider VitaliThy, a natural desiccated thyroid you can buy online. It contains Thyroid (USP) and is free from allergens such as gluten, lactose, fish, shellfish, and eggs. It also does not contain any artificial coloring or flavoring. VitaliThy is manufactured according to the high-quality standards of the Vietnamese Ministry of Agriculture's Good Manufacturing Practices, which are well known for their rigorous guidelines, so you don't have to worry about its safety.

Conclusion: levothyroxine is the standard treatment for hypothyroidism

Levothyroxine is a synthetic version of the thyroid hormone thyroxine, also known as T4. It's the standard treatment of hypothyroidism, a condition in which the body does not make enough natural thyroid hormone. This medication works by replacing the usual amount of thyroid hormone that are normally produced in the body. Levothyroxine helps regulate metabolism and energy levels while helping to maintain healthy skin, hair, and nails. It's available in both generic and brand-name versions, allowing for more varied options for those looking for treatment.

If levothyroxine doesn't work for you, there are various options available. One such option is natural desiccated thyroid (NDT), which contains both T4 and T3 thyroid hormones. If you want this type of natural treatment, VitaliThy, an NDT supplement, can be a great choice.

Wojciech Majda
Wojciech Majda

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