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As is the case with any other medication, there may be some instances where levothyroxine interactions can occur. In such cases, use is not recommended or usage will have to be adjusted in order to prevent or reduce the risk of negative interactions occurring from other drugs, medical conditions, or even food and drink.

Drug Interactions

According to the FDA, drugs that may interact with this medication include the following.

  • Magnesium
  • Calcium and calcium-containing supplements
  • Omeprazole (Prilosec OTC)
  • Prozac (fluoxetine)
  • Warfarin (Jantovin, Coumadin)
  • Adderall

Please note that this list may not be complete, and other interactions with drugs not listed here may occur.

Magnesium

Magnesium oxide taken too soon before or after taking levothyroxine can reduce levothyroxine’s effectiveness and reduce its absorption. Therefore, levothyroxine should be taken at least four hours apart from a magnesium supplement.

Ibuprofen

While experts have widely noted no specific interactions between ibuprofen and levothyroxine, this fact doesn’t mean no interactions exist. If you’re taking levothyroxine, always talk to your medical provider before taking any other medication or supplement, including ibuprofen.

Calcium Supplements (Including Antacids)

Medications and supplements that contain calcium, including antacids, may reduce the body’s ability to absorb levothyroxine and therefore cause levothyroxine to work less effectively. According to Mayo Clinic, you should always take levothyroxine and calcium-containing medications or supplements at least four hours apart.

Omeprazole

Omeprazole (Prilosec OTC®) is used to treat certain stomach problems, like acid reflux (heartburn). Omeprazole works by blocking the secretion of stomach acids, which may interfere with the way levothyroxine works. You should speak with your medical provider before taking omeprazole if you’re currently being treated for hypothyroidism with levothyroxine.

Prozac

Some evidence suggests the antidepressant Prozac® (fluoxetine) may reduce the availability and effectiveness of levothyroxine, therefore leading to reduced thyroid function. According to Harvard Medical School, however, there does seem to be a link between hypothyroidism and depression, and sometimes these medications are prescribed together. Your medical provider should be able to make adjustments to your prescriptions and dosages, change your antidepressant medication, and/or routinely monitor your blood work to make sure you’re not experiencing any adverse interactions.

Warfarin

Taking levothyroxine can increase thyroid hormone levels, which may make you more sensitive to a common blood thinner called warfarin (Coumadin®). For this reason, you may be at a greater risk of bleeding when taking both medications together.

Adderall

Adderall is a type of stimulant from the drug class amphetamines, and is prescribed legally to treat conditions like attention-deficit/hyperactivity disorder (ADHD). Adderall should not be taken with levothyroxine because it can lead to a drug interaction that increases a person’s risk of heart issues like high blood pressure (hypertension), chest pain, and irregular heart beats (arrhythmia). 

Food Interactions

Sometimes the foods we eat and the beverages we drink can also interact with our medications. According to the U.S. National Library of Medicine, food and drink that may interact with this drug include:

  • Alcohol
  • Grapefruit and grapefruit juice
  • Soybeans
  • Walnuts
  • Dietary fiber
  • Certain supplements and herbs

Please note that this list may not be complete, and there may be other foods and beverages that interact with this drug.

Levothyroxine and Alcohol

For more information, please visit our page on levothyroxine and alcohol interactions.

Grapefruit and Grapefruit Juice

Consuming grapefruit, grapefruit juice, or even orange juice can reduce the absorption of levothyroxine and reduce its effectiveness.

Supplements

Certain supplements and food ingredients, including soy, iron supplements (ferrous sulfate), and dietary fiber (psyllium), may reduce the absorption of levothyroxine if consumed too close together. 

Herbs

While the evidence is limited, some studies suggest that certain herbs (including bugleweed and lemon balm) may negatively interact with levothyroxine and thyroid hormones in general, according to Kaiser Permanente.

Disease & Conditions Interactions

Sometimes certain medications can increase the risk of negative side effects for patients with certain diseases or other medical conditions. According to the U.S. National Library of Medicine, diseases and medical conditions that are known to negatively interact with levothyroxine include:

  • Adrenal insufficiency
  • A history of radiation therapy
  • Diabetes
  • Atherosclerosis (hardening of the arteries)
  • Anemia or bleeding problems 
  • Porphyria (group of liver disorders)
  • Osteoporosis
  • Kidney disease
  • Heart disease
  • Heart attack
  • Liver disease
  • Disorders affecting the pituitary gland

Please note that this list may not be complete, and there may be other diseases and medical conditions where patients should not take this medication.

Levothyroxine and Pregnancy

For more information, please visit our page on levothyroxine and pregnancy risks.

Other Interactions

Other potential interactions include the following:

Sun

Some medications can make you more sensitive to sunlight and cause you to burn more easily. This event doesn’t appear to happen with levothyroxine. However, Mayo Clinic notes that some people with thyroids that produce too much thyroxine (a condition known as hyperthyroidism, or overactive thyroid) can make a person’s eyes overly sensitive to light. Such individuals should take extra precautions to protect their eyes.

Disclaimer: this article does not constitute or replace medical advice. If you have an emergency or a serious medical question, please contact a medical professional or call 911 immediately. To see our full medical disclaimer, visit our Terms of Use page.


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