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Levothyroxine (Synthroid) Medication Overview
Levothyroxine, referred to by its brand name Synthroid, treats hypothyroidism. Hypothyroidism is a thyroid condition characterized by low production of thyroid hormone. Levothyroxine for hypothyroidism management is also indicated in surgery and radioactive iodine therapy for the treatment of thyroid cancer.
Normally, the thyroid gland produces thyroid hormones. Thyroid hormones are important to the growth and regulation of energy levels. In conditions such as hypothyroidism, not enough thyroid hormone is produced. Levothyroxine is a hormone medication that helps to replenish low levels of thyroid hormone. In doing so, levothyroxine can mitigate symptoms associated with hypothyroidism.
Medical Indications for Levothyroxine (Synthroid) for Hypothyroidism Management
As previously mentioned, levothyroxine treats hypothyroidism. Hypothyroidism occurs when your thyroid is underactive. Your thyroid is a small gland located at the front of your neck. Although small, it is essential to producing thyroid hormone.
When your thyroid gland is underactive, it does not make enough thyroid hormone. This manifests as symptoms such as weight gain, low energy, drowsiness, constipation, slow speech, hair loss, poor growth, dry skin, muscle and joint pain, depression, cold sensitivity, and irregular or heavy periods.
In addition to treating hypothyroidism, the Food and Drug Administration (FDA) has also approved levothyroxine for the treatment of pituitary thyrotropin suppression. It can be used as an add-on to surgery and radioiodine therapy to help treat certain thyroid cancers.
Dosage
Levothyroxine for hypothyroidism management is available in tablets in 25, 50, 75, 88, 100, 112, 137, 150, 175, 200, and 300 mcg strengths. Your dosage will depend on several factors, including your weight, age, other medications, and cardiovascular status. Your provider will select the dosage that is right for you, and you should take your levothyroxine as they recommend. However, typical dosing is roughly 1.6 mcg/kg daily. For example, if you are an adult weighing 70 kg, your dose will be between 100 to 125 mcg daily, depending on what strength tablet you take.
Your provider can tailor your dose by 12.5 to 25 mcg every four to six weeks until your thyroid labs come back normal. Typically, doses larger than 200 mcg daily are not needed. Certain individuals will require different dosing. For example, elderly individuals may start at a lower dose of 12.5 to 25 mcg daily, which can be adjusted every six to eight weeks. The dose for pediatric patients will also be different.
Levothyroxine (Synthroid) Administration for Hypothyroidism Management
Levothyroxine is typically taken once daily on an empty stomach, usually 30 to 60 minutes before breakfast. You can take levothyroxine with a full drink of water.
Levothyroxine absorption can be affected by other medications you take and specific foods. For certain medications, you may need to space your levothyroxine dose by at least four hours. For certain foods, you may need to space your levothyroxine dose by at least one hour. Your provider may need to adjust your dose depending on the other drugs and foods you take.
Potential Side Effects
Like most drugs, when taking levothyroxine for hypothyroidism management, it can cause both mild and severe side effects. Common side effects will usually resolve upon dose reduction or cessation of therapy. These include:
- Nausea
- Vomiting
- Diarrhea
- Sweating
- Flushing
- Shaking
- Headaches
- Muscle cramps
- Restlessness
- Trouble sleeping
Levothyroxine can also cause serious allergic reactions due to its inactive ingredients. Signs of allergic reaction include itchiness, skin rash, swelling, flushing, hives, stomach pain, nausea, vomiting, diarrhea, wheezing, fever, and joint pain. If you experience any of these effects, seek medical attention right away.
Precautions and Contraindications of Levothyroxine (Synthroid) for Hypothyroidism Management
There are several warnings associated with levothyroxine therapy. These are important to be aware of prior to starting treatment. These include:
- Heart problems in elderly patients and those with underlying heart disease. Too much levothyroxine has been associated with heart issues such as increased heart rate, abnormal heart rhythms, angina, increased thickness of the cardiac wall, and increased heart contractility. Thus, levothyroxine should be started at low doses in these patients.
- Uncontrolled diabetes. In patients with diabetes, levothyroxine may worsen blood sugar levels. This can require increased need for insulin or other antidiabetic medications. Blood sugar should be monitored in diabetic patients on levothyroxine.
- Acute adrenal crisis. Issues with your adrenal glands can occur with levothyroxine if you have pre-existing adrenal insufficiency.
- Myxedema coma. Myxedema coma is a serious and life-threatening condition. Use of oral levothyroxine is not recommended in these instances.
- Low bone density. High doses of levothyroxine can lower your bone mineral density, specifically in women post-menopause. Thus, the lowest dose necessary should be used in these women.
When to Speak to Your Doctor About Levothyroxine (Synthroid)
There are also several people who may not be able to take levothyroxine. In particular, you should discuss with your doctor if you have any of the following conditions:
- Adrenal gland problems
- Heart problems like heart disease, heart failure, or angina
- History of heart attack
- History of allergy to levothyroxine or other medications
- Diabetes
- History of heart attack
- Thyrotoxicosis, an issue characterized by an overactive thyroid gland
Interactions
There are quite a few medications that can affect the absorption and metabolism of levothyroxine. Therefore, it is essential to provide your doctor with a full list of your medications so that they can check for drug interactions. Your levothyroxine dose may need to be adjusted accordingly. The following are examples of medications that can affect levothyroxine:
- Calcium carbonate
- Ferrous sulfate
- Bile acid sequestrants (colesevelam, colestipol, cholestyramine)
- Ion exchange resins (sevelamer, kayexalate)
- Antacids (aluminum, magnesium)
- Proton pump inhibitors
- Sucralfate
- Hydroxides (simethicone)
- Estrogen containing contraceptives
- Estrogens
- Tamoxifen
- Heroin/methadone
- Clofibrate
- Mitotane
- 5-fluorouracil
- Androgens
- Anabolic steroids
- Glucocorticoids
This list is not exhaustive. There are many other medications that can influence how levothyroxine works in the body.
Additional Medications Levothyroxine (Synthroid) Can Impact
- Diabetes medications. Levothyroxine can worsen blood sugar.
- Oral blood thinners. Levothyroxine increases your response to oral blood thinners. Dose adjustments may be needed.
- Antidepressants. Certain antidepressants like tricyclic or tetracyclic antidepressants can interact with levothyroxine.
- Ketamine. Ketamine and levothyroxine together can increase blood pressure and heart rate.
Levothyroxine may also be affected by certain foods. Things like walnuts, soybean flour, dietary fiber, cottonseed meal, and grapefruit juice can affect the absorption of levothyroxine into the body.
Effectiveness and Expectations of Levothyroxine (Synthroid) for Hypothyroidism Management
Levothyroxine is very effective in managing thyroid levels for its labeled indications. In addition, studies have proven that both generic and brand-name levothyroxine produce similar results for thyroid dysfunction.
Long-Term Use and Monitoring of Levothyroxine (Synthroid)
Levothyroxine has a very narrow therapeutic index, meaning it is easy to over or under-treat. Over or under-treatment can impact your heart, bones, cognition, gastrointestinal tract, emotional state, reproductive system, and more. Thus, your provider should increase your dose with caution and monitor for efficacy and safety to prevent these adverse effects.
Additionally, because of the many food and drug interactions with levothyroxine, your provider should monitor how changes to your medication list and diet may affect your levothyroxine therapy.
Alternatives and Complementary Therapies
There are several alternatives to treating hypothyroidism outside of just levothyroxine. These include Armour Thyroid (desiccated thyroid), Cytomel (liothyronine), and Thyrolar (liotrix). Levothyroxine is also sold under several different brand names including Levoxyl, Synthroid, Tirosint, and Unithroid.
There are other natural alternatives to levothyroxine, however, these may not be as efficacious as levothyroxine or efficacious at all. For example, low levels of selenium, vitamin B12, and vitamin D are all associated with thyroid issues. Supplementing, if deficient, with these vitamins and minerals may help to improve thyroid function over time. Some people also turn to herbal supplements such as bladderwack. Bladderwack contains iodine, which is helpful for thyroid issues. Additionally, ashwagandha may help manage thyroid hormone levels.
A great complementary therapy to levothyroxine is to implement a diet that can support your overall health. While there are no specific food recommendations for hypothyroidism, it is important to eat a balanced and nutrient-rich diet. Adding in sources of iodine can also help.
Frequently Asked Questions (FAQs) About Levothyroxine (Synthroid)
When will Levothyroxine (Synthroid) for Hypothyroidism Management start working?
Levothyroxine starts working almost immediately, however, it will not be fully effective until at least four to six weeks of therapy.
When should I take Levothyroxine?
You should take levothyroxine once daily in the morning. Make sure to take it at least 30 minutes prior to having breakfast or having caffeine. Both food and caffeine can affect your body’s ability to absorb levothyroxine.
What do I do if I forget to take Levothyroxine (Synthroid) for Hypothyroidism Management?
If you miss a dose of levothyroxine, take it as soon as possible once you remember. However, if it is close to the time you would take your next dose, do not take it. In this case, you can skip the dose. Never take two doses together.
Can I take Levothyroxine while pregnant?
If you may become pregnant or are pregnant, you should discuss your levothyroxine therapy with your doctor right away. You may have to adjust your treatment as needed (2).
What do I do if I experience side effects?
If you are troubled by the side effects associated with Levothyroxine (Synthroid) for hypothyroidism management, you may need to lower your dose. If you experience uncomfortable side effects, discuss these with your doctor.
Levothyroxine starts working almost immediately, however, it will not be fully effective until at least four to six weeks of therapy.
Resources
- https://medlineplus.gov/druginfo/meds/a682461.html
- https://www.nhs.uk/medicines/levothyroxine/#:~:text=1.-,About%20levothyroxine,is%20only%20available%20on%20prescription.
- https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/021402s024s028lbl.pdf
- https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2771041
- https://www.singlecare.com/blog/levothyroxine-alternatives/