Levothyroxine Side Effects

Levothyroxine is a replacement hormone that helps replace the natural hormones secreted by your thyroid gland. When the thyroid is not functioning at its optimum level, you can take levothyroxine to help regulate the body's metabolism and energy level. You can also use this drug to treat an enlarged thyroid gland brought on by radiation, cancer, surgery or hormone imbalances. This drug will not treat weight issues that come along with thyroid disease.


Levothyroxine is typically taken first thing in the morning. The amount of pills you take will depend on the size of your dose. Your dose may be adjusted over time depending on how your body is reacting to the hormone treatment. Do not stop taking levothyroxine suddenly or without your doctor's knowledge and consent. If you are unable to renew your prescription and you will run out, call your doctor right away so you can find a solution. Stopping your medication unexpectedly can lead to withdrawal symptoms which can lead to more serious side effects. In some cases, levothyroxine has been shown to alter laboratory tests, including liver function examinations. False signs of osteopenia can be found as well.

Common Side Effects of Levothyroxine

Many heart and circulation side effects can occur while on levothyroxine. The most common of these include chest pain, dilated neck veins or increased pulse and blood pressure. These could be serious and will need medical attention if they become serious. If you ever feel like a heart condition is becoming life threatening, call emergency services immediately.

Because levothyroxine affects the glands in your neck, you may notice discomfort in this area as the medication starts to take effect. Swelling in the neck and face are common. These may decrease as your body becomes more used to the medication, but should be monitored to ensure that they do not get worse. If this swelling leads to wheezing, labored breathing, difficulty swallowing or fainting, seek medical attention. Any sign that your condition may be life threatening should be treated like an emergency.

Levothyroxine is a hormone, so it is not uncommon to see hormone changes causing uncomfortable side effects. Heat intolerance, irritability, menstrual changes or nausea are common. As you adjust to your medication these symptoms usually relax. In most cases, these issues are not dangerous and will not impact the patient's ability to function. If they appear to be severe then you can talk with your doctor about how to handle these symptoms.

Uncommon and Rare Side Effects of Levothyroxine

When a prescription is not given at the proper level you can suffer from an overdose. If you notice pulse racing, swelling, shortness of breath, cold, clammy skin, confusion, lightheadedness, hives or rash then you could be dealing with a negative reaction to the medication. This is especially risky if these symptoms appear to come on suddenly. If you start developing one or more of these symptoms, call your doctor immediately. Overdoses should be taken very seriously and you should get emergency help as soon as you notice the symptoms coming on.

Some rare levothyroxine side effects have been reported in some patients. These include dizziness, eye pain, double vision, blurred vision, limping, pain in the hips and knees, seizures or headaches. Some children on levothyroxine have also seen a slowing in their natural growth patterns. While these symptoms are very rare, they should be given proper attention. Talk with your doctor about any side affects you are experiencing so you can determine how to adjust your medication to avoid them. If the side affects you are experiencing impact your ability to function, make an appointment to determine how to proceed. Do not stop taking your medication unless your doctor specifically tells you to.

Side Effects in Children, Pregnant Women, Seniors and Others

Children do not typically suffer from thyroid disease, so overdosing is much more likely if the prescription size is not monitored closely. It is safe to take levothyroxine while you are pregnant, but you should work to keep your prescription consistent to minimalize side effects. Because of the altering hormone levels that occur during pregnancy you will need to adjust your levothyroxine dosage when you become pregnant. Levothyroxine has been shown to pass into breast milk, but no instances of this causing harm to an infant have been reported. If you are concerned about this you can discuss the potential risk with your doctor.

Once you have been prescribed levothyroxine, you will typically be expected to take it for the rest of your life. Taking this drug for long periods of time can lead to bone loss or osteoporosis. If you are at risk for this disease, then check with your doctor about how this might affect you. Seniors will need to be checked regularly to see if they are being affected by this condition.

Those who have suffered a heart attack, thyrotoxicosis or other adrenal gland issues should not take levothyroxine. If you have continuing heart disease or other circulatory issues you should also avoid taking this drug as it increases the risk of having a heart attack.

Interactions with Other Medicines and Substances

If you take oral insulin medications, they may interact with your doses of levothyroxine. You can still take both at the same time, but you should inform your doctor when your insulin doses change so that your levothyroxine dose can be adjusted to match.

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