5 Supplements That Interfere With Thyroid Medication

Over 100 million people will fill a prescription for levothyroxine this year and most of these people have no idea how many things interfere with its function. 

Why does it matter? 

Because if you aren’t taking it correctly then there’s a good chance it’s not going to help you feel better. 

Most people know they shouldn’t take their thyroid medication with obvious things like food and coffee, but few understand this applies to supplements as well!

Which is exactly why today we’re going to talk about supplements that interfere with your thyroid medication so you can be sure you aren’t taking any. 

#1. Biotin

Biotin has a bad reputation among thyroid patients, but most people don’t really understand how or why it can cause problems. 

So let’s set the record straight: 

Biotin does NOT have any impact on thyroid function, but it can interfere with the accuracy of your thyroid lab test results. 

If biotin is taken in high doses before you get your labs tested, it can interfere with the thyroid testing assay and make it look like you have MORE thyroid hormone in your system than you really do (1). 

This means your thyroid lab tests will look hyperthyroid or like you’re taking too much medication. 

But remember:

It’s not actually impacting your thyroid, but it can become a problem if your doctor uses your inaccurate thyroid lab tests to adjust your medication. 

If they do this, then you may end up having your dose reduced unnecessarily leading to more symptoms which is why it’s included on this list. 

If you are someone taking thyroid medication then you must be aware of this interaction or you’re setting yourself up for a bad time! 

The simple solution to the biotin problem is to just avoid taking your biotin dose 2-3 days before you get your labs drawn. 

And this completely solves the problem. 

There’s no need to avoid it, but you do need to make sure you’re using it correctly. 

Use this opportunity to double-check the back of any supplements you’re taking to see if they contain biotin and take that into account when you get your labs drawn next. 

#2. Caffeine 

And let me take the unpopular position here and just say that if you’re taking thyroid medication then you should probably be avoiding caffeine 100%.

This includes coffee, energy drinks, sodas, and pretty much anything else that contains caffeine (2). 

How come? For two main reasons: 

The first is that caffeine speeds up the movement of your intestinal tract which means your thyroid medication spends less time in your gut and less of it gets absorbed. 

And because caffeine has a half-life of 5 hours (meaning each dose stays in your system for 25 total hours (3)), this effect occurs pretty much no matter what time of day you consume it. 

But there’s another reason…

Caffeine has a stimulatory effect on adrenal function and cortisol which can make thyroid-related fatigue even worse. 

And If you’re not careful, you can get into a cycle whereby you are reliant upon caffeine for energy but each dose you take only serves to cause more fatigue in the long run. 

This makes managing your dose of thyroid medication far more complicated than it needs to be. 

#3. Iron and Calcium

For #3, I’ve combined both iron and calcium together because they cause the same issue: 

If taken within 4 hours of your thyroid medication, they can bind to and inactive it. 

Depending on how much iron or calcium you are taking, they can bind up to 25% of your total dose of thyroid hormone (4). 

Higher doses cause higher binding. 

This nasty effect also occurs if you eat foods that are high in iron or calcium which is one of the reasons you’re told to take your thyroid medication on an empty stomach. 

Luckily, the solution is simple: 

Just be sure to take your thyroid medication 4 hours away from any supplements or foods that contain calcium or iron. 

But don’t make the mistake of thinking that iron or calcium are somehow harmful to your thyroid health because they aren’t. 

In fact, your body requires iron to make thyroid hormone! 

And if you are deficient, your body will have a difficult time making what it needs which means you’ll be even more reliant on thyroid medication. 

But as long as you take it 4 hours away from whenever you take your thyroid medication, you’ll be good to go. 

#4. Glucomannan (and other fiber supplements)

Thyroid patients are big fans of glucomannan because of its beneficial effects on weight, appetite, blood sugar, and cholesterol (5). 

These, of course, happen to be some of the biggest and most concerning symptoms that thyroid patients have to deal with. 

But the reason it works so well is also the reason that it interferes with thyroid medication: 

By acting as a sticky glue in your intestinal tract. 

Not only does it slow down the absorption of sugar, thereby positively impacting insulin and appetite, it also slows down the absorption of thyroid medication if taken too close together. 

And if this happens, it will interfere with your thyroid medication and may make your hypothyroid symptoms worse. 

But much like iron and calcium, just because it can cause issues doesn’t mean it has to. 

And you can completely solve this problem by taking glucomannan 4 hours away from whenever you take your thyroid medication. 

So if you like taking your thyroid meds in the morning, you’ll be safe to take glucomannan with lunch which means you can enjoy its effects on appetite pretty much throughout the entire day. 

What about fiber? 

Glucomannan is a soluble fiber, but there are plenty of other types of fiber out there like metamucil, citrucel, benefiber, and so on, which are often used to treat constipation. 

And these fiber supplements can also delay the absorption of thyroid medication, but not quite to the same degree. 

Studies have shown that if you were to take levothyroxine at the same time as metamucil, you’d see a drop in levothyroxine absorption by about 9% (6). 

Not huge, but still enough to cause problems which is why you shouldn’t do it. 

#5. Estrogen enhancing supplements

These are supplements that support and enhance the effects of estrogen and include things like (7): 

• Soy
• Wild yam
• Black cohosh
• Chaste berry
• Flaxseed
• Maca
• Grape
• Ginseng
• Estriol

Many of these are found in supplements targeted toward women’s health and menopause so if you are taking something that is specifically marketed toward women, there’s a good chance that one or more of these might be included. 

It isn’t necessarily a problem if you are on them, because it’s actually critical for women, especially those with thyroid problems, to have a balanced ratio of estrogen to progesterone. 

But you should be aware of their impact on your thyroid. 

Anything that you’re taking that increases estrogen will increase an enzyme known as thyroid-binding globulin. 

And this enzyme is responsible for carrying thyroid hormone throughout your body. 

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Here’s how it works: 

Thyroid hormone is too powerful to just float around in your body so more than 99% of it is bound and unavailable for use by proteins like thyroid-binding globulin (8). 

This leaves a measly 1% of thyroid hormone available for your body to use. 

When you increase estrogen, you increase thyroid-binding globulin, which reduces that 1% even further. 

And if not accounted for with adjustments in your medication, you may inadvertently make your thyroid function worse. 

By the way, even though we’re talking about supplements today, you should know that this same thing occurs if you’re taking an estrogen medication or birth control (9). 

Now, when it comes to supplements, it’s totally worth it to accept this change in thyroid function by increasing estrogen because of how beneficial having a normal estrogen level is. 

But it must be accounted for, usually with an increase in your dose of thyroid medication. 

And the only way to identify that this is happening, is by checking your free thyroid hormones which most doctors don’t do. 

If they are only looking at the TSH, then they will not see these effects. 

This is yet another reason why getting a complete set of thyroid lab tests is so important. 

And if you want to learn which tests every thyroid patient should get, I would recommend checking out this article next.