A replacement hormone therapy, levoxyl or levothyroxine sodium is a common treatment for hypothyroidism (low thyroid hormone). It has also shown effective for treated other issues related to hormone imbalances. Levothyroxine side effects are somewhat common, as with any hormone replacement therapy, so it is important to understand to look out for in combination with treatment. Consider the benefits as well as the side effects to determine if the medication might be right for you.
What Is Levothyroxine Used For?
Levothyroxine is the most commonly prescribed medication in the United States. In fact, millions of individuals take this synthetically produced thyroid hormone. The hormone was first isolated from thyroid extract by biochemist Edward C. Kendall in the early 1900s and then synthesized by Charles R. Harington in 1926. The discovery of the levothyroxine not only changed medicine but has saved millions of lives.
Most commonly levothyroxine is used as a treatment for underactive thyroid. The drug acts to replace or restore the hormone that would normally be produced by the thyroid gland. Low thyroid levels occur naturally as a result of injury by radiation, medication, or total removal by surgery. Having adequate supplies of thyroid hormone is essential to maintain normal mental and physical activity. Likewise, in children having sufficient thyroid hormone helps maintain normal physical and mental development.
Levothyroxine has also been found effective for treating other issues related to thyroid disorders or hormone imbalances. The treatment may be used to remedy goiters or certain types of thyroid cancers. The medication should not, however, be used to treat infertility unless the issue is caused by low thyroid hormone.
Potential Levothyroxine Side Effects
Understanding the potential side effects is important in determining if the treatment is right for you. As with any medication or hormone replacement therapy, thyroxine is not without potential side effects. Some of the side effects are more common than others.
Common Levothyroxine Side Effects
Common side effects include:
- Increased appetite.
- Weight loss.
- Heat sensitivity.
- Excessive sweating.
- Mood changes.
- Changes in menstrual cycles.
- Hair loss (typically temporary).
- Stomach cramps.
Most of these common symptoms are mild and will go away within a couple of days to a few weeks. If, however, the side effects are more severe or do not go away in a few days, you should talk to your doctor and/or pharmacist.
Serious Side Effects
In some cases, levothyroxine may cause serious side effects. If you experience any of these levothyroxine side effects, you should call your doctor immediately. If you feel your symptoms are life-threatening or constitute a medical emergency, call 911. Serious levothyroxine side effects include:
- Heart attack, with symptoms such as chest pain, shortness of breath, or upper body discomfort.
- Heart failure, include symptoms like shortness of breath, extreme fatigue, swelling in your extremities, and unexpected weight gain.
- Very fast heart rate.
- Irregular heart beat.
This is not an exhaustive list of the possible levothyroxine side effects because medications affect each individual differently. However, this list does represent the most commonly reported side effects of the drug. You can report any additional side effects you may experience to the FDA and discuss other potential concerns with your doctor or pharmacist.
Thyroxine may also interact with other drugs, herbs, or vitamins you are currently taking. An interaction occurs when a substance you are taking alters the way a medication is intended to work. Interactions may be harmful or may even prevent the drug from working effectively.
To avoid potential interactions, you should provide your doctor with a comprehensive list of all of the medications, supplements, vitamins, herbs, and illegal drugs you are currently taking. Your doctor or pharmacist can help you manage your medications carefully and determine if levothyroxine will interact with any of the other medications you are taking.
Interactions That May Increase Levothyroxine Side Effects
Combining levothyroxine with certain medications may result in an increased risk for certain side effects. Drugs that may cause interactions include:
- Antidepressants including amitriptyline, sertraline, and maprotiline. The side effects of thyroxine and antidepressants may increase if you combine the drugs. You may also be at a higher risk for irregular heartbeats or arrhythmias if you combine these drugs.
- Sympathomimetic drugs like pseudoephedrine and albuterol. The effects of both of these medications may increase if taken together. This combination may also put you at risk for serious heart complications.
- Blood thinners including warfarin. Taking a blood thinner in combination with levothyroxine may increase your risk of bleeding. Your doctor may need to adjust your dosage of blood thinner if you are taking it along with levothyroxine.
- Ketamine. Taking ketamine while on levothyroxine may increase your risk of a fast heart rate and high blood pressure.
Interactions That May Make Thyroxine Less Effective
When you combine levothyroxine with certain medications, it may not work as effectively to treat your health condition. This interaction is typically a result of a decrease in levothyroxine in your body. Drugs that may cause this type of interaction include:
- Rifampin and anti-seizure medication including phenobarbital and carbamazepine.
- Calcium carbonate or ferrous sulfate. To make sure levothyroxine works properly, you should take it at least four hours prior to either of these medications.
- Colesevelam, colestipol, cholestyramine, kayexalate, or sevelamer. To ensure that thyroxine works effectively, take it at least 4 hours prior to any of these medications.
- Simethicone or antacids including aluminum or magnesium.
- Cancer medications that are in the tyrosine-kinse inhibitors class, like imatinib.
Other Drugs That May Become Less Effective
In some cases the other medications you take along with levothyroxine may not be as effective. This typically occurs because the amount of the drugs in your system is decreased. Examples of this type of interaction include:
- Diabetes drugs including insulin and metformin, among others. Your doctor may need to adjust your dosage of these drugs if taken in combination with thyroxine.
- Digoxin. Your doctor may need to increase your dose of this drug if taken in combination with levothyroxine.
- Theophyline. Your doctor may need to monitor your theophylline levels if you take it while taking thyroxine.
Appropriate doses of levothyroxine is based on your weight, body mass, pregnancy status, etiology of hormone imbalance, age, and several other factors. Your doctor will work closely with you to determine an appropriate dose for your healthy needs, taking other medications and health conditions into consideration.
Levothyroxine is a life-saving medication used to treat hypothyroidism and other hormonal imbalances. Like most medications, it is not without its side effects. However, when balanced with other medications and taken as directed by a physician most side effects can be effectively managed and/or prevented.