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January 03, 2023 6 min read

Grapefruit has long been a popular addition to breakfast plates and diets alike, with many claiming it can help you lose weight. Some people even swear by "the Grapefruit Diet," which is believed to speed up the body's natural metabolism and help you lose weight quickly. It's tasty and healthy – what's not to like? But did you know that grapefruit may actually interfere with the effectiveness of your thyroid medication? That's right - if you're taking thyroid medication, consuming grapefruit could be doing more harm than good. So, should you try a grapefruit diet to combat weight gain due to hypothyroidism? Keep reading to find the answer!

What you need to know about thyroid medications

Your thyroid is an incredibly important gland in your body. It helps to regulate your metabolism and keep everything running smoothly. Your thyroid produces and releases thyroid hormones, including thyroxine (T4) and triiodothyronine (T3). These hormones help control many functions in the body, like temperature regulation, digestion, and energy levels.

The production of these hormones is controlled by a hormone known as Thyroid Stimulating Hormone (TSH). This hormone is released from the pituitary gland, which acts as a kind of "command center" for the entire endocrine system.

If your thyroid doesn't produce enough hormones, you have a condition called hypothyroidism. This condition can make life uncomfortable since it causes symptoms like cold intolerance, fatigue, and weight gain.

The two common medications used to treat hypothyroidism are levothyroxine and natural desiccated thyroid (NDT). Levothyroxine is a synthetic form of the T4 hormone. Some of the most popular brands of levothyroxine are Synthroid and Unithroid. NDT, on the other hand, is made from dried pig or cow thyroids, which contain both T4 and T3 hormones. Some popular brands of NDT medications are Armour Thyroid and WP Thyroid. There are also NDT supplements, like VitaliThy, which contain the same ingredients as NDT medications.

Although both meds have been proven effective when it comes to managing hypothyroidism symptoms like weight gain, NDT is the preferred option for many hypothyroid patients.

What are the benefits of grapefruit?

Known for its sweet yet slightly tart flavor with notes of bitterness and a high water content, grapefruit has a lot to offer. Aside from its delicious and refreshing taste, this citrus fruit is packed with nutrients, vitamins, and minerals. They're also low in calories but loaded with antioxidants. That's why grapefruit is known as one of the healthiest fruits with endless benefits - from helping improve digestion to boosting immunity and even weight loss.

Among the most sought-after benefits of grapefruit is weight loss because it's a rich source of dietary fiber - half of a medium-sized grapefruit contains 2 grams of fiber. This means that it can help make you feel fuller longer, so you can reduce your calorie intake.

In addition to dietary fiber, grapefruit has more than 15 beneficial vitamins and minerals, such as vitamins C and A, as well as folic acid, protein, potassium, thiamine, folate, and magnesium. Therefore, grapefruit consumption may help lower your blood pressure, promote heart health, benefit your immune system, help with digestion, and protect your skin from aging and sun damage. It may also decrease your risk of stroke, cancer, and diabetes.

levothyroxine and grapefruit

What about grapefruit juice?

It may seem more convenient to drink grapefruit juice than to eat the whole fruit. But while you can get some of the vitamins and minerals by drinking grapefruit juice, you can't really use it as a substitute for whole fruit.

Just like any fruit juice, grapefruit juice tends to deliver higher concentrations of sugar, and this can drive up your blood glucose levels quite quickly. That's why drinking grapefruit juice can be counterproductive – instead of reaping the benefits, you may face a health problem.

What is the grapefruit diet?

If you're trying to lose weight due to hypothyroidism, you might have heard about the grapefruit diet.

Dating back to the 1930s, the grapefruit diet has been around for a long time. It was one of the first fad diets to burst onto the health and wellness scene that gained major popularity. Also known as the Hollywood Diet, it promises rapid weight loss due to claims that the fruit contains enzymes that can help burn fat. Supporters of this fad diet believe that the diet may help you lose up to 10 pounds in just 12 days.

Obviously, you'll be chowing on a lot of grapefruits, but you don't have to limit yourself to eating nothing but grapefruits. Instead, you can create a protein-rich meal plan that incorporates grapefruits or grapefruit juice. Most versions of this diet also cut calories; some suggest limiting yourself to as low as 800 calories a day.

But despite the many claims that grapefruit has a special fat-burning enzyme, there's no scientific research to back up these assertions. It's true that the dietary fiber in grapefruit can help you feel fuller faster and for a longer period of time, but it doesn't burn or melt your fat.

Plus, eating an excessive amount of grapefruit when you have hypothyroidism and taking thyroid medication may cause more harm than good. It can lead to dangerous drug interactions.

How does grapefruit affect thyroid medications?

Eating or drinking grapefruit while taking thyroid hormone replacement medication can reduce the amount of medication that enters your bloodstream. This means that the medication won't work as effectively, so your thyroid hormone levels will stay low, and you'll still experience hypothyroidism symptoms.

So how does grapefruit interfere with the absorption of thyroid medications?

Here's why - grapefruit contains furanocoumarins, organic compounds that affect an enzyme called CYP3A4. This enzyme plays an important role in breaking down certain medications in your body so that they can be absorbed. Consuming large amounts of grapefruit may also interfere with the activity of CYP3A4 in the liver. When this enzyme is inhibited, your thyroid medication may not be metabolized as quickly and absorbed as properly, reducing its benefits.

In a case study published in the British Journal of Clinical Pharmacology, it was described how the levels of thyroid hormone in a 36-year-old woman using levothyroxine fell below therapeutic levels due to extensive consumption of the citrus fruit. This really shows how grapefruit and levothyroxine interaction can really reduce the absorption of levothyroxine.

Most studies are for levothyroxine and grapefruit. However, grapefruit may also interact with NDT.

Can I still eat grapefruit?

Absolutely! While grapefruit may interfere with your thyroid medication, you can still enjoy it – as long as you know how to do it right.

The first rule is to separate your NDT or levothyroxine dose and grapefruit intake by at least 4 hours. This will ensure that your thyroid medication has been fully absorbed by your body. The second rule is to avoid eating this citrus fruit excessively. You can enjoy it once in a while, but not with every meal you have each day.

What other medications are affected by grapefruit?

In addition to hypothyroid medications, grapefruit juice also affects a few other drugs. Other medications that rely on the CYP3A4 enzyme for metabolization and absorption, such as cyclosporin and felodipine, may also be affected by grapefruit.

Furthermore, grapefruit juice can also decrease the plasma concentrations of some drugs by inhibiting intestinal uptake transporters. These medications include levothyroxine, fexofenadine, and celiprolol.

What other things interact with thyroid medication?

Aside from grapefruit, many foods and beverages can also influence the effectiveness of your thyroid medication. These include (but are not limited to):


Calcium supplements and calcium found in food can interfere with the absorption of your thyroid medication in the gastrointestinal tract. Since calcium is important, you shouldn't avoid them. Instead, make sure that you get your calcium intake at least 4 hours away from your thyroid medication.

Caffeinated products

You should never drink coffee or other caffeinated beverages like green tea together with your thyroid hormone replacement medication. Ideally, you need to wait at least an hour after taking your meds.

What's the best way to take your thyroid medication?

Besides grapefruit juice - levothyroxine interaction or grapefruit juice - NDT interaction, you need to keep in mind that all kinds of foods and drinks, except water, can affect your thyroid hormone replacement medication in different ways. Therefore, always take your medication on an empty stomach. The recommended time is as soon as you wake up in the morning, an hour before breakfast.

What's the best diet to help you lose weight with hypothyroidism?

There is no "best" diet to help you lose weight with hypothyroidism. Some diets, like the grapefruit diet, can be dangerous for your thyroid health.

The best way to lose weight if you have low levels of thyroid hormone is to fix the underlying problem by taking thyroid hormone replacement medication. While levothyroxine is well-tolerated by most people, you might want to consider taking NDT if your main goal is to lose the weight you've gained due to hypothyroidism. A study of 70 hypothyroid patients found that after 16 weeks on levothyroxine and 16 weeks on NDT, people lose 4 pounds effortlessly on NDT.

There are many NDT brands available on the market, such as VitaliThy, a natural desiccated thyroid you can buy online. This NDT supplement contains Thyroid (USP) and has a complex composition that'll help you combat weight gain due to an underactive thyroid gland.

Wojciech Majda
Wojciech Majda

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