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A pill organizer and a prescription pad: Can you take biotin and Synthroid together?
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Can you take biotin and Synthroid together?

Taking biotin within days of a thyroid function test can cause false results that might affect your thyroid treatment plan
Gerardo Sison medical writer headshot
By | Aug. 21, 2024
In this article:

Many people taking Synthroid (levothyroxine) for thyroid problems might also take biotin to supplement their health or to manage Synthroid side effects like hair loss. While biotin is known for its benefits for hair and nails, there are potential interactions to consider if you’re taking thyroid medication. Biotin can interfere with thyroid function tests, causing misleading results and possibly affecting your treatment plan. 

Biotin can lead to falsely low TSH levels, making it hard to accurately monitor thyroid health. Therefore, it’s important to tell your healthcare provider about any supplements you are taking, including biotin, to avoid any complications with your thyroid treatment plan. 

What is Synthroid?

Synthroid is the brand name for the medication levothyroxine, which is a synthetic version of the thyroid hormone thyroxine (T4). The thyroid gland produces this hormone naturally. When it does not produce enough hormones, a condition known as hypothyroidism, healthcare providers often prescribe Synthroid.

Synthroid works by supplementing the body’s hormone levels, which may help people with hypothyroidism maintain a normal metabolism and energy levels. It is also approved by the Food and Drug Administration (FDA) to treat thyroid cancer alongside surgery and radioiodine therapy. 

Synthroid comes in various strengths, typically measured in mcg (micrograms). You might be prescribed a common dosage of 25 mcg, 50 mcg, or 100 mcg once daily. 

How does biotin work?

Biotin, also known as vitamin H or B7, is part of the B vitamin group. It plays a role in various biochemical processes in the body. Biotin helps convert food into energy by supporting enzymes involved in the metabolism of fats, carbohydrates, and proteins.

Biotin acts as a coenzyme, meaning it helps enzymes carry out their functions. In particular, it may help process fats and amino acids, which may be used to build proteins. As a result, it may help maintain healthy skin, hair, and nails.

Biotin is naturally found in various foods, such as eggs, nuts, and seeds. However, biotin supplements are widely available and often included in multivitamin preparations. The vitamin is water-soluble, so excess amounts are typically cleared through the urine.

Why some people take biotin

Biotin may offer various health benefits as a dietary supplement. Here are some reasons why someone might choose to take it.

Promotes hair growth

Biotin is often associated with healthier, stronger hair. Many people, including those on Synthroid, take biotin to reduce hair loss and promote new hair growth. Hair thinning and loss can be symptoms of thyroid issues, so biotin may provide a simple and accessible solution.

Supports healthy skin

Biotin helps maintain healthy skin. It is known to improve skin hydration, smoothness, and appearance. Those on Synthroid may take biotin because thyroid imbalances can lead to skin problems, and this supplement may help counteract those effects.

Strengthens nails

Biotin can improve the thickness and hardness of nails, which is beneficial for fragile and brittle nails. Since Synthroid users often experience nail issues due to thyroid conditions, adding biotin to their routine may offer a straightforward fix.

Improves energy levels

Biotin helps convert food into energy. Many people with hypothyroidism may experience fatigue and low energy levels. Biotin may help improve energy levels and reduce tiredness.

May help improve cognitive function

Some evidence suggests that biotin could support brain health and cognitive function. Individuals with thyroid issues sometimes face cognitive challenges, making biotin an attractive supplement for improving mental clarity and sharpness.

Supports cardiovascular health

Biotin may also contribute to heart health by maintaining healthy triglyceride levels. People on Synthroid who are at risk of cardiovascular problems due to thyroid dysfunction might use biotin to support their heart health.

Assists in blood sugar regulation

Biotin may help regulate blood sugar levels. This is particularly important for those on Synthroid, as thyroid problems can sometimes lead to blood sugar irregularities. Taking biotin may offer a way to help balance these levels.

The FDA does not approve dietary supplements, including biotin, for any purpose. Instead, it generally regulates drugs claiming to treat, diagnose, prevent, or cure diseases.

Does biotin interfere with Synthroid?

Biotin does not directly interact with Synthroid. However, biotin can interfere with thyroid function tests, which are used to monitor the effectiveness of Synthroid treatment. High doses of biotin can lead to inaccurate results in thyroid hormone assays, potentially causing misinterpretation of thyroid function. As a result, a healthcare provider might make improper changes to Synthroid dosages.

Biotin can interfere with thyroid tests because it affects the biotin-streptavidin interaction used in many immunoassays. Excess biotin can falsely elevate or lower the levels of thyroid hormones. For example, the test may show reduced thyroid stimulating hormone (TSH) levels and increased free thyroxine levels, which might lead to a misdiagnosis of hyperthyroidism or Graves disease.

Therefore, if you take biotin supplements, tell your healthcare provider, especially before undergoing thyroid function tests. This precaution helps ensure that test results accurately reflect your thyroid status.

How do thyroid tests work?

Thyroid-stimulating hormone and free thyroxine levels are key measures for evaluating thyroid function. Thyroid lab tests include immunoassays, which are methods used to measure these hormone levels. 

Here are the main types of thyroid tests:

  • TSH (thyroid-stimulating hormone): This test measures the level of TSH in your blood. High levels of TSH may indicate an underactive thyroid, while low levels may suggest an overactive thyroid.
  • Free T4 (thyroxine): This test measures the amount of free thyroxine in your blood. Free T4 is the active form of thyroxine that is available to your tissues. Abnormal levels can help diagnose thyroid disorders.
  • Free T3 (triiodothyronine): This test measures the amount of free triiodothyronine in your blood. Free T3 is another active thyroid hormone; its levels can help diagnose hyperthyroidism and other thyroid conditions.

These immunoassay tests, which use antibodies to detect and measure specific hormones in the blood, involve taking a small blood sample from your arm. The sample is then mixed with antibodies that bind to the thyroid hormones. If the hormones are present, they will attach to these antibodies, allowing healthcare professionals to measure levels accurately. This helps determine whether your thyroid is functioning normally or whether there are any issues, such as an underactive or overactive thyroid.

One key part often used in these tests is streptavidin, a protein that has a high affinity for a molecule called biotin. In the lab, streptavidin is used to capture and hold onto biotin-labeled antibodies, which bind to the thyroid hormones in your blood sample. By using streptavidin, the tests can be more sensitive and specific, providing reliable information about your thyroid health.

When to stop biotin before thyroid testing

According to the American Thyroid Association (ATA), it is generally recommended that patients stop taking biotin at least two days before their thyroid test to avoid any risk of interference. However, more recent advice from the ATA suggests that it might be safer to wait at least three to five days before the test. This longer waiting period helps ensure that the biotin is fully cleared from your system, reducing the risk of any test inaccuracies.

How to take Synthroid correctly

If you take Synthroid, you’ll want to make sure you take it correctly to ensure its effectiveness and maintain stable thyroid hormone levels. Here are some key factors to consider to optimize the absorption and effectiveness of Synthroid:

  • Timing: Take Synthroid on an empty stomach, ideally 30–60 minutes before breakfast.
  • Consistency: Take it at the same time every day to maintain steady hormone levels in your bloodstream.
  • Water intake: Swallow the pill with a full glass of water to help it dissolve properly and absorb efficiently.
  • Medication interactions: Be aware of other medications you are taking that may affect Synthroid absorption. Always consult your healthcare provider or pharmacist before starting any new medication.
  • Storage: Store Synthroid at room temperature, away from light, moisture, and heat to maintain its effectiveness.

Following these guidelines can help ensure that Synthroid works effectively for your thyroid condition.

RELATED: Can you take Synthroid at night?

Other Synthroid interactions

In addition to biotin, many drugs and supplements can interact with Synthroid, potentially affecting its absorption, metabolism, or effectiveness. Some commonly used medications and supplements that may interact with Synthroid include the following.

Phosphate binders

Drugs like Fer-In-Sol (ferrous sulfate), Renagel (sevelamer), Fosrenol (lanthanum), and calcium-based products like Tums (calcium carbonate) can bind to levothyroxine and reduce its absorption. To avoid reduced effectiveness, take Synthroid at least four hours before or after taking these.

Antacids

These medications can decrease the absorption of levothyroxine by reducing stomach acidity. Common examples include Maalox (aluminum hydroxide and magnesium hydroxide), Mylanta (aluminum hydroxide and magnesium hydroxide), and Gas-X (simethicone). Close monitoring is needed if these are used together.

Proton pump inhibitors (PPIs)

These medications can also decrease the absorption of levothyroxine by reducing stomach acidity. Common examples of PPIs include Nexium (esomeprazole), Prilosec (omeprazole), and Prevacid (lansoprazole). 

Bile acid sequestrants

Medications such as Welchol (colesevelam), Questran (cholestyramine), and Colestid (colestipol) can interfere with levothyroxine absorption. It is recommended to wait at least four hours before taking these drugs if you’ve taken Synthroid.

Glucocorticoids

Medications such as Deltasone (prednisone) and Decadron (dexamethasone) can alter thyroid hormone levels by decreasing the conversion of T4 to T3. Regular monitoring of thyroid function tests is necessary when using these medications with levothyroxine.

Antidepressant therapy

The use of tricyclic antidepressants such as Elavil (amitriptyline) or tetracyclic antidepressants like Ludiomil (maprotiline) with Synthroid may increase the effects of both drugs. This can happen because the body becomes more sensitive to certain chemicals. Possible side effects include a higher chance of heart problems. Also, Synthroid can make the antidepressants work faster. If you take Zoloft (sertraline) and are also on Synthroid, you might need a higher dose of Synthroid.

Antidiabetic medications 

The use of Synthroid in people with diabetes may worsen blood sugar control and require increased antidiabetic or insulin requirements. You may need to monitor blood sugar control with a healthcare provider, especially when thyroid therapy is started, changed, or discontinued.

These are only some of the medications that can interact with Synthroid. It’s important to tell your healthcare provider about all medications you take, including other prescription drugs, over-the-counter medicines, and herbal supplements. 

Other biotin interactions

Although biotin itself does not directly interact with other drugs, some medications can affect biotin levels in the body.

Antibiotics

Long-term antibiotic use may reduce biotin levels. This can occur because antibiotics destroy gut bacteria that produce biotin. Examples include:

  • Amoxil (amoxicillin)
  • Cipro (ciprofloxacin)
  • Vibramycin (doxycycline)
  • Bactrim (sulfamethoxazole/trimethoprim)
  • Levaquin (levofloxacin)
  • Keflex (cephalexin)

Anticonvulsants

Medications for seizures can also lower biotin levels. Long-term use can reduce the body’s biotin stores. Common anticonvulsants include:

  • Carbatrol (carbamazepine) 
  • Luminal (phenobarbital) 
  • Dilantin (phenytoin) 
  • Mysoline (primidone)

Always consult a healthcare provider before starting new medications. 

RELATED: Biotin side effects and how to avoid them