Table of Contents
III. How to Avoid Synthroid Side Effects
IV. Synthroid Drug Interactions
V. What is Considered a High Dose of Synthroid?
Synthroid, also known as levothyroxine, is considered the first-line treatment for hypothyroidism, according to the American Thyroid Association. [1] When taken properly as directed, Synthroid can safely and effectively provide the thyroid hormone your body needs.
While Synthroid is considered the gold standard thyroid medication, [1] it's important to be aware that, like any medication, it can potentially cause side effects or interact with other substances. In this article, we'll provide an overview of potential Synthroid side effects and drug interactions, as well as tips for taking it safely and effectively.
What is Synthroid?
Synthroid is a once-daily oral medication that was approved by the FDA in 2002 to treat hypothyroidism and thyrotropin-dependent thyroid cancer. [2]
Synthroid works by restoring normal thyroid hormone levels in the body. Its active ingredient, levothyroxine, is a synthetic hormone that functions similarly to thyroxine (T4), a hormone naturally produced by the thyroid gland. [2]
By replacing the T4 that is typically made by the thyroid, Synthroid helps patients achieve normal thyroid function. Thyroid replacement therapy with Synthroid is usually a lifelong commitment. [2]
The American Thyroid Association recommends generic levothyroxine or brand-name Synthroid as the first line of treatment for hypothyroidism. [1] Aside from being affordable and easy to take, there are several other reasons levothyroxine is preferred:
- It effectively relieves hypothyroidism symptoms. Normal T4 and TSH levels are usually achieved within six weeks of starting treatment.
- It has a low risk of side effects when taken in recommended amounts.
- It is well absorbed in the gut, with 70 to 80% of the tablet being absorbed.
- It has a long half-life of seven days, allowing for once-daily dosing.
- It provides a natural ratio of T4 to T3 that mimics normal thyroid function. [1]
Synthroid Side Effects
When taking Synthroid, it is important to be aware of potential side effects that may occur. These side effects are typically a result of receiving an excessive amount of medication, known as overtreatment. [3]
To ensure you are taking the proper dosage, it’s crucial to let your doctor know if you experience any of the following symptoms:
- Hair loss
- Nervousness
- Irritability
- Chest pain
- Shortness of breath
- Irregular heartbeat
- Fast heartbeat
- Excessive sweating
- Vomiting
- Diarrhea
- Change in appetite
- Weight loss
- Low fertility
- Decreased bone density
- Changes in menstrual periods
- Muscle weakness
- Muscle spasms [3]
If you experience any concerning symptoms after starting Synthroid or increasing your dosage, let your doctor know right away.
The best way to keep track of your side effects is by maintaining a symptom journal or log while you are taking Synthroid. You can review this information with your doctor to determine if your dose needs adjustment or if other treatments are needed.
How to Avoid Synthroid Side Effects
Most Synthroid side effects arise from an improperly high dose. If you experience any side effects from Synthroid, contact your doctor right away so they can adjust your dosage accordingly. [3]
Aside from improper dosing, there are some preventable causes of Synthroid side effects to be aware of:
- Diet: Certain foods can interfere with Synthroid absorption or processing in your body. Try to avoid eating large amounts of foods containing soy, cottonseed meal, walnuts, grapefruit juice, or excess dietary fiber. Let your doctor know if you regularly consume any of these foods so they can modify your Synthroid dosage. [4]
- Medications: Some medications can disrupt the way Synthroid works in your body. To prevent this, inform your doctor of any other medications or supplements you take so they can evaluate potential interactions with Synthroid. [4]
- Diabetes: For those with diabetes who take Synthroid, it's important to know it can worsen glycemic control. If this occurs, be sure to notify your doctor so they can adjust your diabetes medications [2]
Synthroid Drug Interactions
When starting a new medication like Synthroid, it's important to keep your doctor informed about everything else you're taking. Certain medications and supplements can interact with Synthroid, making it less effective or increasing side effects.
- Iron and calcium supplements: Calcium and iron supplements should be taken four hours before or after your Synthroid dose. These minerals can bind to Synthroid and prevent proper absorption. [2]
- Orlistat: If you are taking orlistat while also taking Synthroid, your doctor will monitor you for any changes in thyroid function. [2]
- Bile acid sequestrants: These medications are commonly prescribed to lower LDL cholesterol levels. [5] However, they can also interfere with the absorption of Synthroid in your body. To avoid this issue, it is recommended to take Synthroid at least four hours before or after taking bile acid sequestrants. [2]
- Ion exchange resins (IERs): IERs are substances added to certain medications to enhance their absorption in the body. [6] They are also used independently to regulate potassium [7] or phosphorus [6] levels. If you are taking an IER, it is important to consult your doctor as it may affect the absorption of Synthroid. To avoid any potential interactions, take Synthroid four hours before or after taking IERs. [2]
- Proton pump inhibitors (PPIs): PPIs are medications commonly used to reduce stomach acid production. However, Synthroid relies on stomach acidity to aid in its absorption. When taken together, PPIs can interfere with the absorption of Synthroid. If you are prescribed PPIs along with Synthroid, your doctor may closely monitor your thyroid hormone levels to ensure proper medication effectiveness. [2]
- Phenobarbital: Primarily prescribed for seizures and insomnia, [8] Phenobarbital can accelerate the breakdown of Synthroid, potentially resulting in reduced T4 serum levels. If you are taking Phenobarbital, your healthcare provider may need to adjust your Synthroid dosage accordingly. [2]
- Rifampin: The antibiotic Rifampin increases Synthroid metabolism. You'll likely need a higher Synthroid dose to compensate. [2]
- Amiodarone: Used to regulate irregular heartbeats, [9] Amiodarone can impact thyroid hormone levels by inhibiting the conversion of inactive T4 to active T3. Your healthcare provider will monitor your thyroid hormone levels closely if you are taking Amiodarone alongside Synthroid. [2]
- Antidepressants: Certain types of antidepressants can intensify the side effects of both the antidepressants and Synthroid when taken together. Your doctor may need to adjust your medication regimen or dosages. [2]
What is Considered a High Dose of Synthroid?
When starting Synthroid, finding the optimal dose is a careful balancing act. Your doctor considers several factors to determine the right dosage for you, including your:
- Age
- Weight
- Cardiovascular status
- Pregnancy status [2]
The reason for this precision is that thyroid hormone levels need to be maintained within a specific range. In fact, Synthroid is available in twelve dosages to ensure you can take the exact dosage needed to treat your hypothyroidism. Taking too much Synthroid can push your levels too high and lead to symptoms of hyperthyroidism. [3]
It's important to note that what may be considered a high dosage for one individual could be beneficial for another, depending on their medical history and symptoms. Your doctor’s goal is to find the lowest Synthroid dose that treats your hypothyroidism. [3]
Taking an excessive dose of Synthroid can lead to symptoms such as:
- Hair loss
- Nervousness
- Irritability
- Chest pain
- Shortness of breath
- Irregular heartbeat
- Fast heartbeat
- Excessive sweating
- Vomiting
- Diarrhea
- Change in appetite
- Weight loss
- Low fertility
- Decreased bone density
- Changes in menstrual periods
- Muscle weakness
- Muscle spasms [3]
If you experience any of these symptoms, it could indicate that your dosage is too high for your condition. [3] It's crucial to inform your doctor about any symptoms that you are experiencing.
Conclusion
Synthroid can be an effective treatment for hypothyroidism when taken appropriately. By taking Synthroid exactly as prescribed by your doctor and being mindful of potential interactions with other medications, supplements, and certain foods, side effects are often minimal.
However, if you experience side effects, it’s important to let your doctor know immediately. Synthroid typically only causes side effects when the dosage is too high for you.
The information provided is for informational purposes only. We do not offer medical advice. Please consult with your physician or qualified healthcare professional for guidance on drugs, medical conditions, or treatments. Our content is not a replacement for professional medical recommendations.