Synthroid interactions: A detailed guide

This article describes possible interactions with Synthroid. Interactions can cause a drug to have a different effect on the body than expected. Interactions can occur due to medications, alcohol, or certain health conditions.

Synthroid has a boxed warning. A boxed warning is the most serious warning from the Food and Drug Administration (FDA). For details, see the end of this article.

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Other drugs and Synthroid

The drugs in the list below may interact with Synthroid. This article doesn’t include all drugs that may interact with Synthroid.

Drug classes or drugs that may interact with Synthroid include:

• diabetes drugs:
  • drug examples: insulin glargine (Lantus, others), glipizide (Glucotrol XL)
  • what might happen: can make the diabetes drug less effective
• antacids:
  • drug examples: calcium carbonate (Tums), aluminum hydroxide/magnesium hydroxide/simethicone (Mylanta)
  • what might happen: can make Synthroid less effective
• beta-blockers:
  • drug examples: propranolol (Inderal LA, InnoPran XL), carvedilol (Coreg)
  • what might happen: can make the beta-blocker less effective
• bile acid sequestrants:
  • drug examples: colesevelam (Welchol), cholestyramine (Locholest, Prevalite)
  • what might happen: can make Synthroid less effective
• phosphate binders:
  • drug examples: sevelamer (Renvela, Renagel), lanthanum (Fosrenol)
  • what might happen: can make Synthroid less effective
• proton pump inhibitors:
  • drug examples: omeprazole (Prilosec), esomeprazole (Nexium)
  • what might happen: can make Synthroid less effective
• amiodarone (Pacerone):
  • what might happen: can make Synthroid more or less effective; can increase the risk for side effects of Synthroid
• digoxin (Lanoxin):
  • what might happen: can make digoxin less effective
• orlistat (Xenical, Alli):
  • what might happen: can make Synthroid less effective
• sucralfate (Carafate):
  • what might happen: can make Synthroid less effective
• warfarin (Jantoven):
  • what might happen: can increase the effect and risk of side effects of warfarin

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Other interactions and Synthroid

Interactions can occur with supplements, foods, vaccines, and some lab tests. Below you can learn whether Synthroid has these interactions. 

The information below doesn’t include all possible interactions with Synthroid.

Synthroid and supplements

Before taking Synthroid, tell your doctor and pharmacist about any herbs you take, as well as vitamins and supplements. Doing so may help you avoid interactions.

If you have questions about interactions that may affect you, talk with your doctor or pharmacist.

Synthroid and herbs

Synthroid isn’t known to interact with herbs. But this doesn’t mean interactions with herbs can’t happen or won’t be identified later.

Because of this, talk with your doctor or pharmacist before taking any of these products during your Synthroid treatment.

Synthroid and vitamins and minerals

Synthroid may interact with several minerals that are available as supplements, including:

• calcium
• chromium
• iron
• magnesium

Taking any of these mineral supplements with Synthroid can make Synthroid less effective. This interaction occurs because these minerals can decrease how well your body absorbs Synthroid. If you take any of these mineral supplements while taking Synthroid, you should separate the doses by at least 4 hours.

Synthroid can also interact with biotin supplements. Biotin supplements may interact with tests used to check your thyroid hormone levels. These tests help your doctor determine how well Synthroid is working to treat your condition. For accurate test results, you should not take biotin supplements for at least 2 days before getting thyroid hormone tests. If you’re taking biotin supplements, tell your doctor before having lab tests.

Synthroid and food

It’s important to follow special instructions to avoid food interactions with Synthroid, as taking Synthroid with food makes this medication less effective. You should take Synthroid on an empty stomach with only plain water.

After taking Synthroid, you should wait at least 30 to 60 minutes before drinking coffee or beverages other than plain water or consuming food.

Talk with your doctor or pharmacist if you have more questions about possible food interactions with Synthroid.

Synthroid and vaccines

Synthroid isn’t known to interact with vaccines. But this doesn’t mean interactions with vaccines can’t happen or won’t be identified later.

Because of this, talk with your doctor or pharmacist before receiving any vaccines during treatment with Synthroid.

Synthroid and lab tests

Synthroid isn’t known to interact with lab tests. But this doesn’t mean interactions with lab tests can’t happen or won’t be identified later.

Because of this, talk with your doctor or pharmacist before having any tests while taking Synthroid.

Synthroid and cannabis or CBD

Studies of cannabis (commonly called marijuana) and cannabis products have been shown to interact with Synthroid. Cannabidiol (CBD) is an example of a cannabis product.

Cannabis can increase or decrease the amount of Synthroid in your system. This could make the drug less effective, or increase your risk for side effects.

Before you take Synthroid, tell your doctor and pharmacist if you use cannabis. Doing so may help prevent possible interactions.

Note: Cannabis is illegal at a federal level but is legal in many states to varying degrees.

When to avoid Synthroid

Certain health conditions or other factors could increase some risks with Synthroid. Because of this, doctors may not prescribe Synthroid in these cases. These health conditions or other factors are called contraindications.

Here’s a contraindication for Synthroid:

• Adrenal insufficiency that isn’t managed: If you have adrenal insufficiency that isn’t treated, taking Synthroid may cause an adrenal crisis. Typically, doctors will treat adrenal insufficiency using a corticosteroid before prescribing Synthroid to treat your thyroid condition.

Before you start taking Synthroid, talk with your doctor about the drug’s contraindications. They can recommend whether you should take Synthroid.

Alcohol and Synthroid

Synthroid is not known to interact with alcohol. If you drink alcohol, talk with your doctor about whether it’s safe to consume it during treatment with Synthroid.

Health factors and Synthroid

Certain medical conditions or other health factors may increase the risk of interactions with Synthroid. Keep in mind that interactions could lead to side effects or affect how well the drug works. Before taking Synthroid, tell your doctor about your health history. They’ll determine whether Synthroid is right for you.

These health conditions or other factors might interact with Synthroid:

• adrenal gland problem, such as adrenal insufficiency
• problem with blood clotting, such as hemophilia
• heart condition, such as atrial fibrillation
• osteopenia, osteoporosis, or another condition that causes weak bones
• type 1 or 2 diabetes
• pregnancy or breastfeeding
• past allergic reaction to Synthroid

Preventing Synthroid interactions

You may be able to help avoid certain interactions with Synthroid. Before taking this drug, you may want to discuss possible interactions with your doctor and pharmacist.

Things to consider include:

• Whether you drink alcohol or use cannabis.
• Other medications and herbs you take, as well as vitamins and supplements. Your doctor or pharmacist can help you fill out a medication list.
• What to do if you’re prescribed a new drug while taking Synthroid.

Taking Synthroid exactly as prescribed can also help prevent interactions.

Boxed warning for Synthroid

Synthroid has a boxed warning stating that the drug should not be used for weight loss purposes or to treat obesity. A boxed warning is the most serious warning from the Food and Drug Administration (FDA).

Synthroid should not be used to treat obesity or to help with weight loss. In people with a healthy thyroid, Synthroid and other thyroid hormone replacements do not work for weight loss. Additionally, Synthroid and other thyroid hormones can cause serious or life threatening side effects when taken in large doses.

This risk is further increased if the medications are combined with other drugs, such as phentermine, which may be prescribed for weight loss.

To learn more, talk with your doctor.

Disclaimer: Optum Perks has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.