What are the long-term side effects of taking Synthroid? | Ro (2023)

Levothyroxine sodium, sold under brand names such as Synthroid, Unithroid, Levoxyl, and Tirosint, is a commonly used prescription medication for hypothyroidism. These man-made, synthetic drugs replace the hormone, thyroxine or T4, that your thyroid would normally produce.

Since most people with hypothyroidism are able to live with potentially ongoing treatment, it makes sense to investigate potential long-term side effects.

What is Synthroid used for?

Synthroid (or generic levothyroxine) is used for thyroid hormone replacement therapy in people with low thyroid hormone levels (Hypothyroidism). It can also be used to treat certain forms of thyroid cancer in combination with other treatments (DailyMed, 2019).

There is no cure for hypothyroidism, a condition that affects about 5% of the population and affects the entire body (Chiovato, 2019). However, thyroid replacement drugs such as levothyroxine can help manage the condition and reduce the symptoms of hypothyroidism, such as fatigue and exhaustion, sensitivity to colds, hair loss, and weight gain.

The purpose of levothyroxine and its Synthroid counterpart is to bring T4 and TSH (thyrotropic hormone) back to normal levels by providing the body with a synthetic version of the same hormone. Basically, the correct dose of Synthroid mimics normal thyroid function.

Most sources say it takes four to eight weeks to feel better on Synthroid (DailyMed, 2019). Your doctor will check your TSH blood test about six weeks after starting treatment to make sure your thyroid hormone levels are back to normal. This means you are getting the right amount of thyroid hormone.

Synthroid is usually taken once a day, preferably on an empty stomach. To increase effectiveness, avoid using prescription or over-the-counter antacids.

What are the short term side effects of Synthroid?

It should be noted that the U.S. Food and Drug Administration (FDA) has issued a black box warning for levothyroxine: Levothyroxine should not be taken for weight loss. High doses of levothyroxine can lead to serious and potentially life-threatening side effects (DailyMed, 2019).

As you and your doctor search for the right dose of Synthroid or levothyroxine, you may feel some discomfortside effects— are usually the result of an incorrect dose. The symptoms of low thyroxine are basically what you experienced with hypothyroidism.

However, it is also possible that some side effects may occur due to taking too much thyroid hormone - the dose of Synthroid is too high, leading to a condition called hyperthyroidism.

Be sure to seek medical advice if you experience any of the following side effects so that your dose can be adjusted (DailyMed, 2019).

• Fast or abnormal heartbeat
• Headache
• Chest pain or difficulty breathing
• Increased irritability or nervousness or tremors (shaking)
• Problems with sleeping
• Excessive sweating and inability to cope with the feeling of heat (heat intolerance)
• Changes in appetite and possible diarrhea
• Vomiting or weight changes
• Leg cramps
• Weak muscles
• Fever for no apparent reason
• Changes in your period.

If the dose of levothyroxine is too high, serious side effects can occur, mainly affecting the heart, including (DailyMed, 2019):

• Irregular heart rate (arrhythmias)
• High blood pressure
• Cardiac arrest
• chest pain (angina)
• Heart attack (myocardial infarction)
• Cardiac arrest (heart stops beating)

Get medical help right away if you notice any of these symptoms or experience any side effects that get worse.

What are the long-term side effects of taking Synthroid?

Synthroid (and levothyroxine) is considered a safe and effective therapy. Ultimately, you and your doctor will decide on the long-term effective dose. People have been taking these drugs for decades - usually for life.

That's why it's a good idea to talk to your doctor about whether you're taking the right amount of thyroid hormone. Ideally, you should take the lowest dose possible to get your thyroid deficiency under control. Therefore, doctors often start with a low dose and then adjust the dose based on response (Chiovato, 2019).

There are two possible side effects of long-term use that should be discussed with your doctor: bone thinning (or osteoporosis) and heart problems.

osteoporosis

When bones become thinner and lose weight, they become weaker and more likely to fracture or fracture. Over time, a condition called osteoporosis can develop. Osteoporosis is not necessarily an inevitable part of aging: a healthy diet and lifelong weight-bearing exercise can help maintain healthy skeletal bones.

High levels of levothyroxine can accelerate bone loss, essentially reproducing what would happen if you had hyperthyroidism. As you age, your thyroid needs change, so the dose that works for you at 40 may be too high at 60. Lifelong monitoring is necessary to maintain balanced thyroid hormone levels. Researchers are still investigating whether people overtreated with levothyroxine lose bone mass faster, increasing their risk of osteoporosis.

A study conducted in Korea in 2014 over the age of 65 looked at the association between a higher dose of levothyroxine and the risk of bone fractures. They found that women who were already at increased risk of osteoporosis had more bone fractures when they took higher doses of levothyroxine.Namely, in 2014).

Another study found that if TSH levels were within the normal range, there was no increased risk of fractures (Thayakaran, 2019). So if you are taking the right dose of levothyroxine for your body, you are less likely to develop osteoporosis.

One way to reduce your risk of developing osteoporosis is to regularly test your TSH blood. This will help keep your levothyroxine dose in line with your thyroid hormone needs. Another option is to have your bone mineral density checked regularly to see how your bone density changes over time.

This is especially important for women over 50, as menopause also leads to a loss of estrogen (which protects bones). Finally, your doctor may recommend a calcium supplement or a weight-bearing exercise program to help improve bone health.

heart problems

It is well known that abnormal levels of thyroid hormones can affect the heart. Researchers continue to study the long-term effects of Synthroid and other thyroid replacement drugs on the heart (Udovčić, 2017 (monographs).).

If you don't monitor your hormone levels carefully and get too much thyroid hormone (hyperthyroidism), it can lead to heart problems over time. You may experience a rapid heartbeat, chest pain and tightness, and even a heart attack. Fast or irregular heartbeat (egatrial fibrillation), palpitations and arrhythmias should be treated appropriately. High levels of thyroid hormones can also lead to heart failure (Klein, 2007. (encyclopedia entry).).

On the other hand, if your levothyroxine dose is too low, you increase the risk of intoxicationcholesterolIheart diseasewhich can lead to myocardial infarction and stroke (Klein, 2007). So you can see that optimal heart health depends on a balanced thyroid hormone system.

Application

The best way to avoid the long-term side effects of taking Synthroid is to work closely with your doctor to ensure you are taking the optimal dose of Synthroid, especially as your needs change over time. Not too low and not too high. Be consistent. And check your TSH regularly.