What is levothyroxine?
Levothyroxine (or L-thyroxine) is a synthetic form of thyroxine (also known as T4), a hormone produced by your thyroid gland.
Like natural thyroxine, your body converts levothyroxine into another hormone, triiodothyronine (also known as T3), which plays an important role in metabolism, as well as regulating heart rate and the production of protein.
Levothyroxine is usually taken orally, most commonly in the form of tablets ranging from 12.5 micrograms (mcg) to 300 mcg. Soft gel capsule and liquid forms have been developed in recent years and are starting to become more widely available.
Levothyroxine is the generic name for the medication. It is also sold under brand names, including Levothroid, Levoxyl, Synthroid, Tirosint, and Unithroid.
What is levothyroxine used for?
Levothyroxine is used to treat hypothyroidism, which means the body does not produce enough (or any) thyroxine.
Hashimoto's thyroiditis is the most common form of hypothyroidism.
People who live with hyperthyroidism (meaning the thyroid produces too much thyroxine) may also require levothyroxine. This is because treatment for hyperthyroidism can involve destroying the thyroid gland, thus leading to no production of thyroxine at all.
Similarly, people who receive treatment for other thyroid conditions, such as goiter or thyroid cancer, may subsequently require levothyroxine.
How and when do I take levothyroxine?
Levothyroxine works best when taken on an empty stomach, so it is usually recommended that it is taken in the morning 30-60 minutes before breakfast.
Levothyroxine most commonly comes in tablet form. If possible, it should be swallowed whole without being crushed or chewed, along with a glass of water.
For infants, children, and adults who have trouble swallowing, tablets can be crushed, mixed with one or two teaspoons of water, and administered with a spoon or medicine dispenser pipette. The mixture should be taken immediately and not stored.
Levothyroxine can also come in the form of a solution, which may be taken with or without water. It is important to ensure the ampoule containing the solution is completely emptied so you receive the entire dose. You can do this by squeezing it at least five times.
If you are mixing the levothyroxine solution with water, drink the mixture and then rinse the inside of the glass with a little more water and drink this as well. This helps make sure you ingest all the medication.
Other ways of taking levothyroxine, such as via injections, are less common and will likely require detailed instructions.
Regardless of the way in which you take levothyroxine, it is important to follow the instructions provided by the manufacturer and to discuss any concerns with your doctor or pharmacist.
How long after eating can I take levothyroxine?
It is usually recommended that you wait at least 30 minutes, and ideally at least one hour, before eating after taking levothyroxine. You should also avoid drinking anything other than water during this time.
Can I take levothyroxine at night?
Although it is routinely recommended that levothyroxine is taken in the morning, there is research that suggests it may be better absorbed at night.
It has also been argued that some foods that interfere with levothyroxine absorption, such as calcium, iron, and high-fiber food, are more commonly eaten for breakfast than evening meals.
However, consistency is hugely important in levothyroxine treatment, and many people find it much easier to achieve this consistency in the morning than at night.
You can discuss these aspects of your dietary and lifestyle habits with your doctor, together with whom you can decide the time of day that suits you best.
What is the correct dosage of levothyroxine?
The correct dosage of levothyroxine is determined by factors such as your age, weight, the severity of hypothyroidism, and other medical conditions you live with.
Typically, a “full replacement” dose starts at 1.6 mcg per kilogram of weight per day (mcg/kg/day). This is often prescribed to non-elderly and otherwise healthy individuals who are newly-diagnosed with hypothyroidism.
The dosage may be adjusted by 12.5-25 mcg every 4 to 6 weeks until hormone levels are normalized.
Both the starting dose and time between adjustments vary depending on the factors mentioned above. For example, a person with severe, long-lasting hypothyroidism may start on a dose of 12.5-25 mcg, which may be adjusted every 2 to 4 weeks.
Finding the correct dosage can be a lengthy process; your dosage may need adjusting several times before you are clinically euthyroid and TSH (thyroid-stimulating hormone) levels return to normal. Your body may only be able to tolerate small increases at any time.
Once the correct dosage has been found, an evaluation may be made every 6 to 12 months or when there is a change in your clinical status (for example, if you are diagnosed with another health condition, or there is a significant change in your weight).
How long does it take for levothyroxine to work?
Thyroxine is a slow-acting hormone. Although levothyroxine starts working immediately, it usually takes at least a week, and often up to six weeks, before your symptoms start to improve. It is around this time that your doctor will likely test your thyroid hormone levels and adjust your dosage accordingly.
What are the side effects of levothyroxine?
Many people do not experience side effects when taking levothyroxine. Hair loss can occur in the first few months of levothyroxine treatment but is usually temporary as your body adjusts.
If you experience more serious side effects, it is important to contact your doctor immediately. These can include:
- Chest pain
- Fast, pounding, or irregular heartbeat
- Swelling hands, ankles, or feet
- Seizures
- Shortness of breath
- Shaking
- Bone pain
- Headaches
- Sweating
- Increased sensitivity to heat
- Fatigue
- Diarrhea
Serious allergic reactions to levothyroxine are rare. If you do experience signs of a serious allergic reaction, seek medical attention immediately. Symptoms include:
- Rash
- Itching and swelling, particularly of the face, tongue, and throat
- Trouble breathing
- Severe dizziness
Can I buy levothyroxine over the counter?
No. Levothyroxine is only available with a prescription.
What happens if I stop taking levothyroxine?
Do not stop taking levothyroxine unless told to do so by your doctor.
In most cases, hypothyroidism is a lifelong disease and requires lifelong levothyroxine treatment.
If you stop taking levothyroxine, your thyroid hormone levels will likely drop, and you may begin to experience the typical symptoms of hypothyroidism. These include:
- Abnormal blood pressure
- Weight gain
- Increased risk of heart disease
- Dry skin
- Hair loss
- Often feeling cold
- Fatigue
- Muscle weakness
- Aches, pain, and numbness in joints and muscles
- Depression
- Elevated cholesterol
- Constipation
It is important to take levothyroxine as prescribed. Speak to your doctor if you have any concerns about your treatment.
What happens if I miss a dose of levothyroxine?
If you forget to take a dose, take it as soon as you remember, unless it's almost time for your next dose. In which case just skip the forgotten dose. Do not take 2 doses together to make up for a missed dose.
Can I take levothyroxine when pregnant or breastfeeding?
Yes. If you are pregnant, an underactive thyroid can cause problems with the development of your baby and increase the risk of a miscarriage, so it is important to continue taking levothyroxine.
Pregnant women usually need to increase their dosage of levothyroxine, especially early in the pregnancy. It is therefore important to speak to your doctor as soon as you think you may be pregnant.
Your doctor will monitor your thyroid hormone levels regularly throughout your pregnancy.
It is also safe to take levothyroxine while breastfeeding.
Can I take levothyroxine to lose weight?
No. Manufacturers of levothyroxine clearly state that it should not be used alone or in combination with other drugs for the purpose of weight loss. Taking levothyroxine when your thyroid is producing normal levels of thyroxine can lead to symptoms associated with hyperthyroidism.
These symptoms can be serious and even life-threatening.
If you would like to lose weight, speak to your doctor about the options available.
Can I drink alcohol while taking levothyroxine?
Yes. There is no evidence to suggest alcohol interacts with levothyroxine or how the body absorbs it, so drinking alcohol within usual guidelines is considered to be safe.
However, it is worth bearing in mind that alcohol has been shown to inhibit the production of thyroid hormones, while hypothyroidism has also been linked to reduced alcohol tolerance.
Does levothyroxine interact with food, supplements, and other medications?
Certain foods may decrease your body’s absorption of levothyroxine. These include:
- Soybean flour (infant formula)
- Walnuts
- Dietary Fiber
- Cottonseed meal
Grapefruit juice delays the absorption of levothyroxine and its bioavailability (the amount of the drug that enters your circulation and becomes active).
Iron, calcium supplements, and antacids may also decrease absorption.
Levothyroxine should not be taken within 4 hours of the above agents.
According to Drugs.com, levothyroxine interacts with 590 different medications. Among them are:
- Levothyroxine and Adderall: Adderall is the most common brand name for amphetamine. When taken in combination with levothyroxine, it can increase your risk of cardiovascular side effects such as high blood pressure, chest pain, irregular heartbeat, and palpitation.
- Levothyroxine and metformin: levothyroxine can reduce the effectiveness of metformin and other diabetes medication. Blood sugar levels should be monitored closely during levothyroxine treatment; your doctor may need to alter your diabetes treatment accordingly.
- Levothyroxine and phentermine: phentermine is an appetite suppressant. When taken in combination with levothyroxine, it can increase your risk of cardiovascular side effects such as high blood pressure, chest pain, irregular heartbeat, and palpitation.
It is important to discuss all medications, supplements, vitamins, and minerals you take with your doctor, as well as your dietary habits, to avoid the risk of interactions with levothyroxine. Do not rely solely on this article, or any other webpage.
The content on this page is provided for informational purposes only. If you have any questions or concerns about your treatment, you should talk to your doctor, pharmacist, or healthcare professional. This is particularly important if you are taking multiple medications or have any existing medical conditions.
