6 Foods to Avoid If You’re Taking Levothyroxine (Synthroid)

Levothyroxine (Synthroid) is one of the most commonly prescribed medications in the U.S. It replaces thyroid hormone in people with hypothyroidism. It’s also used as part of treatment for some types of thyroid cancer.

Taking levothyroxine at the right time is an important part of making sure it works as intended. That’s why you need to take it with water on an empty stomach, either 30 to 60 minutes before breakfast or several hours after your last meal.

There aren’t any foods or drinks you need to completely avoid while taking levothyroxine. But certain foods and drinks can interact with levothyroxine and reduce how much of the medication your body absorbs. This can make your treatment less effective and lead to changes in your thyroid hormone levels.

1. Soy

Soy can block how well your body absorbs levothyroxine. Researchers think soy proteins can bind to levothyroxine in your digestive tract. This lowers the amount of medication available for your body to absorb. 

This effect is most noticeable in infants with congenital hypothyroidism who are fed soy formula. But experts think soy may also reduce levothyroxine absorption in adults as well.

It’s reasonable to wait at least 1 hour after taking your thyroid medication before eating soy products. Examples of soy products include:

• Tofu

• Edamame

• Soy milk

• Miso

• Tempeh

• Natto

• Soy supplements

2. Cow’s milk

Calcium supplements can reduce how much levothyroxine your body absorbs by binding to the medication in your stomach. That’s why experts recommend waiting at least 4 hours after taking levothyroxine before taking a calcium supplement.

Calcium-rich foods, like cow’s milk, may have a similar effect. But there isn’t strong evidence showing that these foods significantly interfere with levothyroxine absorption. You don’t need to avoid or limit calcium-rich foods while taking levothyroxine. But it’s reasonable to wait at least 1 hour after taking your thyroid medication before eating them.

In addition to cow’s milk, examples of calcium-rich foods include:

• Yogurt

• Cheese

• Fortified plant-based milks

• Calcium-fortified orange juice

• Cottage cheese

• Ice cream and frozen yogurt

3. Fruit juice

Some fruits and their juices may reduce how much levothyroxine your body absorbs. Researchers think these juices interfere with transport proteins that help move levothyroxine from your digestive tract into your bloodstream.

Fruit juices that have been linked to lower levothyroxine absorption include:

• Grapefruit 

• Papaya

• Orange 

• Grape

But not all studies have found a strong effect. It’s also not clear exactly how much juice a person needs to drink to trigger this interaction. 

To be safe, it’s best to take levothyroxine with water instead of juice. If you enjoy juice with breakfast, wait at least 1 hour after taking your medication before drinking it.

4. Walnuts

Walnuts may reduce how much levothyroxine your body absorbs. Researchers think this happens because compounds in walnuts can bind to levothyroxine in your gut. This keeps the medication from being absorbed.

There isn’t a lot of evidence around this interaction. So it’s not clear how many walnuts someone needs to eat to see this effect. 

To help your body absorb levothyroxine, wait at least 1 hour after taking your medication before eating walnuts. If you regularly eat a lot of walnuts and your thyroid levels are unexpectedly high, tell your healthcare team. They may ask you to change your walnut intake to see if that helps bring your thyroid levels into a healthy range.

5. Coffee

Coffee can lower how much levothyroxine your body absorbs. Researchers think this happens because compounds in coffee can bind to the medication, speed up digestion, and affect stomach acid levels.

The good news is that you don’t have to give up coffee. And if you take a liquid or soft-gel form of levothyroxine, coffee appears to have much less of an effect on absorption. For most people, it’s a good idea to wait at least 1 hour after taking levothyroxine before drinking coffee.

6. Fiber-rich foods

High-fiber foods may bind to the levothyroxine in your gut, keeping some of it from reaching your bloodstream.

Most of the research has focused on wheat bran. But experts think other high-fiber foods may have a similar effect. This interaction appears to be most important for people who eat a very high-fiber diet or regularly take fiber supplements.

Examples of high-fiber foods include:

• Wheat bran and bran cereals

• Lentils

• Black beans

• Chickpeas

• Split peas

• Oats

• High-fiber fruits and vegetables, such as raspberries and pears

This doesn’t mean you need to avoid fiber. In fact, fiber has many health benefits. But it’s best to wait at least 1 hour after taking levothyroxine before eating high-fiber foods or taking fiber supplements.

Let your healthcare team know if you regularly eat a high-fiber diet. They may review your diet, adjust the timing of when you take your medication, or change your levothyroxine dose if your thyroid levels aren’t in a healthy range.

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Written by:

Brian Clista, MD

Dr. Clista is a board-certified pediatrician who works in private practice in Pittsburgh, Pennsylvania. He previously served as a National Health Service Corporation Scholar in the inner city of Pittsburgh for 11 years.

Edited by:

Patricia Pinto-Garcia, MD, MPH

Patricia Pinto-Garcia, MD, MPH, is a medical editor at GoodRx. She is a licensed, board-certified pediatrician with more than a decade of experience in academic medicine.

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