7 of the Best Supplements for an Underactive Thyroid

Natural Ways to Help Get a Slow-Moving Thyroid Back on Track

• Thyroid Results|
• 1. Probiotics|
• 2. Vitamin D|
• 3. Selenium|
• 4. Inositol|
• 5. Ginger|
• 6. Adrenal Supplements|
• 7. Hydrochloric acid|
• Gut–Thyroid Link|
• Iodine|
• Big Picture|

Given that you’re reading this, you’re probably looking for natural ways to relieve underactive thyroid symptoms, such as weight gain, brain fog, constipation, and fatigue.

This article will guide you through what I consider to be the 7 best supplements for treating underactive thyroid symptoms and supporting healthy thyroid function, based on research and my own clinical experience. 

However, before we jump too far ahead, I urge you to ask your healthcare provider to check and interpret your thyroid hormone levels. Your lab results will help determine if dietary supplements are the right course of action for your thyroid problem. Depending on your numbers, you may benefit from thyroid supplements, thyroid hormone medication, improving your gut health, or a combination of these.Let’s break this down a bit more before getting into the potential health benefits of thyroid supplements.

Using Thyroid Results to Guide Treatment 

A simple thyroid panel that measures thyroid-stimulating hormone (TSH) and free thyroxine hormone (free T4) can yield useful, actionable information, including whether supplements will be useful.

With TSH and free T4 levels at our fingertips, it is relatively straightforward to figure out which therapy will benefit which hypothyroid condition the most. 

For most adults (who aren’t pregnant, and who are under 60):

• A TSH level above 4.5 IU/mL with a free T4 level below 0.8 ng/dL indicates true or overt hypothyroidism, for which thyroid hormone medication is the best treatment [1, 2].
• A high TSH (4.5–10 IU/mL) with normal free T4 (0.8−1.8 ng/dL) suggests subclinical hypothyroidism, which can be treated with supplements and diet changes [2, 3].

Most thyroid panels also check for thyroid peroxidase (TPO) antibodies to look for the autoimmune condition, Hashimoto’s thyroiditis. Having Hashiomoto’s increases your risk of developing clinical or subclinical hypothyroidism in the future. True hypothyroidism with Hashimoto’s thyroiditis looks like:

• TSH above 4.5 IU/mL, free T4 below 0.8 ng/dL, and TPO antibodies over 500 IU/mL [1, 4, 5] 

Luckily, tackling the underlying autoimmunity with thyroid supplements can bring high TPO antibody levels down. A TPO result of less than 35 IU/mL is considered negative for these thyroid antibodies, which means you do not have Hashimoto’s.

Sometimes my clients have what appear to be thyroid symptoms (fatigue, brain fog, weight gain, and joint aches), but their TSH, free T4, and TPO antibodies are all within the normal ranges. When this happens, something else may be affecting their overall health and contributing to a “sluggish thyroid.” You guessed it: I’m talking about gut imbalances.

Here’s a quick summary of thyroid lab results, the conditions they suggest, and what treatments I often recommend to my clients with symptoms of hypothyroidism:

The bottom line is that supplements can be particularly useful in people with subclinical hypothyroidism. Supplements may also play a supportive, secondary role in Hashimoto’s thyroiditis and complement the effects of hormone therapy for clinical hypothyroidism. That said, improving the diet and gut health should be a top priority, no matter what.

With that in mind, let’s now delve into those 7 thyroid supplements, starting with arguably the most useful supplement to support thyroid health—probiotics. 

1. Probiotics

Because of the close link between the gut and the thyroid gland (more about this below), probiotics are a good supplement to help optimize thyroid function and thyroid hormone production.

This is more than just hypothetical: There’s growing evidence to link taking probiotics with improved outcomes for people with Hashimoto’s disease and hypothyroidism.

For example, a 2020 clinical trial involving patients with hypothyroidism found that supplementation with synbiotics (a combination of probiotics and prebiotics) appeared to improve fatigue and reduce TSH levels after 8 weeks. 

People in the study also needed less of the thyroid medication, levothyroxine [6], perhaps because when probiotics improve gut health, the intestines can absorb and utilize the thyroid medication more effectively.

Other research has shown that probiotics can lift depression [7], which is so common with an underactive thyroid. And probiotics can fight infections like Helicobacter pylori and small intestinal bacterial overgrowth (SIBO), which are associated with thyroid dysfunction [8, 9, 10].

I have generally found the best results when my clients with underactive thyroid symptoms include microbial strains from the three main categories of probiotics, which are:

• A blend of Lactobacillus and Bifidobacterium strains
• Saccharomyces boulardii (a beneficial yeast)
• A soil-based probiotic

Typically, 2–3 months on these probiotics is enough to ensure maximum effectiveness. And we’ve made triple therapy easier by putting all three probiotic types in just one small packet.

2. Vitamin D

Vitamin D deficiency is common, and low levels of vitamin D are associated with hypothyroidism [11]. It therefore makes sense to increase your vitamin D levels if you have concerns about a lethargic thyroid.

Generally speaking, it’s better to boost your vitamin D levels through safe sun exposure. In fact, evidence suggests that sunshine is the optimal way to get most of our vitamin D requirements [12]. You can find more details on the right amount of sun exposure for different skin types in this article on vitamins for gut health.  

However, vitamin D supplements may be helpful if you have high TPO antibodies (remember, high TPO is a sign that you have thyroid autoimmunity that could lead to hypothyroidism). 

According to three meta-analyses:  

• Taking vitamin D supplements in the dosage range of 1,000–8,000 IU per day for 3–6 months can lower TPO antibodies by an average of 158 points [13, 14]. 
• It may take at least 3 months of supplementing to see benefits [15].

Typically, I recommend that my clinical and subclinical hypothyroid clients take Vitamin D with vitamin K for immune support. If their vitamin D is below 40, we use 10,000 IU per day. Once their levels are in the 40s, we use 4,000–6,000 IU per day.

To keep track of your vitamin D status, you can have your vitamin D levels tested easily and affordably. Getting tested every 6 months is about what it takes to arm my clients with the knowledge they need to adjust their sun exposure or supplements as needed.

3. Selenium

The mineral selenium may also be helpful when it comes to lowering TPO antibodies. 

For example, a meta-analysis of multiple studies found that TPO antibodies dropped an average of 271–512 points in those who took selenium supplements [16]. 

Another meta-analysis showed that selenium supplementation reduced thyroid antibodies for at least a year in patients who also took prescription thyroid medication. Selenium had a similar, though temporary, effect in patients who did not take medication [16].

While selenium appears to be great for reducing thyroid antibodies, another meta-analysis found that it doesn’t seem to affect thyroid hormone levels associated with an underactive thyroid [17].

So, when my clients have elevated TPO antibodies, I often recommend a trial of selenium (200 micrograms [mcg] every other day) before retesting their thyroid labs to see how they respond. I’ve also seen selenium help improve subclinical hypothyroidism. What’s great about selenium is that it isn’t expensive, and it’s generally safe to try. 

It’s also possible to get more benefit from selenium by combining it with the next supplement on our list: inositol. 

4. Inositol

Some studies have shown that a combination of inositol and selenium works better for hypothyroidism than selenium alone [18, 19]. You may have seen inositol referred to as vitamin B-8, but it’s not really a vitamin. Inositol (aka myoinositol) is a form of carbohydrate the body makes to help our cells interact with their environment [20]. Inositol is available in some foods (meat, fruits, corn, beans, grains, and legumes) and as a supplement. 

Inositol may be able to help the thyroid gland become more responsive to TSH, which could explain how, when combined with selenium, it can help to reduce both thyroid antibodies and TSH [18]. 

One clinical trial looked at 48 patients who were positive for thyroid antibodies and had TSH levels between 4 and 10. The patients were randomized to take either selenium plus inositol, or selenium alone. 

• After 6 months, both the selenium group and the selenium plus inositol group had a similar drop (42–44%) in TPO antibodies. 
• However, only the group taking selenium and inositol in combination saw a 31% drop in their TSH levels, too [18]. 

A 2020 study also found that people who took a combo of inositol and selenium for 12 months had their TSH levels drop from 4.7 to 2.9, on average [19].

The daily doses used were 83 mcg of selenium (in the form of selenomethionine) and 600 mg of inositol. For my clients with Hashimoto’s and subclinical hypothyroidism, I often recommend 200 mcg of selenium and 600 mg of inositol per day. 

5. Ginger

Ginger supplementation may help some hypothyroid patients who still have symptoms even though their hormone medication has normalized their TSH. Its anti-inflammatory properties may pave the way for ginger to benefit those with stubborn symptoms of an underactive thyroid.

For example, in a randomized controlled clinical trial of hypothyroid patients with persistent symptoms, those who took ginger supplements had significant reductions in [21]: 

• Weight gain
• Cold intolerance
• Constipation 
• Dry skin
• Appetite loss
• Memory loss 
• Poor concentration 
• Body weight
• Waist circumference
• TSH levels

I typically recommend that all of my hypothyroid clients take 550 mg of ginger per day to help reduce inflammation and persistent symptoms.

6. Adrenal Supplements

Certain herbal treatments that target adrenal function may also help with thyroid function or symptoms of low thyroid, particularly fatigue. 

The adrenal glands produce numerous hormones—including cortisol, epinephrine, and norepinephrine—that can impact energy levels.

Herbal supplements that studies have shown can improve thyroid health or hypothyroid-like symptoms include:

• Ashwagandha: A 2018 randomized controlled trial found that patients with subclinical hypothyroidism who took 600 mg of ashwagandha daily had improved TSH, T3, and T4 levels after 8 weeks compared to those taking a placebo [22]. 
• Ginseng: A 2018 systematic review of 10 studies found that ginseng improved fatigue, a symptom often associated with thyroid dysfunction [23]. 
• Rhodiola: A 2009 randomized controlled trial found that rhodiola improved stress-related symptoms and thinking ability [24]. 

For my hypothyroid clients with lingering fatigue, I might recommend adrenal support for 2–3 weeks. If they don’t have noticeable improvements in energy, mood, and sleep, then they probably don’t need adrenal support.

7. Hydrochloric Acid (HCl)

The effect of hydrochloric acid supplements like betaine HCl isn’t well documented, but I find that some clients do find hydrochloric acid really helpful for underactive thyroid issues.

Typically, I’ll have my clients consider HCl if they’re older than 65 and have a history of anemia, autoimmunity, or upper GI symptoms like heartburn, belching, and/or excess fullness after meals.

HCl can correct low stomach acidity, and people with low stomach acid are more likely to have thyroid symptoms or abnormal thyroid lab results.

For example, one study showed that 40% of patients with atrophic gastritis (inflammation of the stomach, which leads to low HCl) also had autoimmune thyroid disease [25]. Similarly, people with stomach cell autoimmunity (which also causes low HCl) often have TPO antibodies [26]. 

And a recent study found that patients with low stomach acidity required 23% higher doses of levothyroxine to achieve the same thyroid hormone levels as levothyroxine users with normal stomach acidity [27]. 

However, it can be hard to determine whether HCl is beneficial when other gastrointestinal symptoms or imbalances are present.

For this reason, I always suggest that my clients take steps to improve their general gut health first. Often, a rebalanced gut can normalize stomach acid without the need for supplements. Hydrochloric acid is still an option after the functional gut work (diet, probiotics, etc.) is complete.

You Can’t Separate Gut and Thyroid Health 

Significant research backs a connection between gut health and thyroid health [28], yet healthcare professionals often overlook it.

At the clinic, we’re used to meeting people with hypothyroid symptoms that clear up after they improve their gut health. In fact, we published a case series and literature review to alert other functional and integrative practitioners to the observation that gut and thyroid health are often intertwined.

To be more specific, depression, brain fog, fatigue, and a general lack of well-being can be symptoms of an underactive thyroid disorder. But these are also symptoms that can stem from poor gut health. 

When these symptoms occur along with thyroid labs that are in the suboptimal range of normal, some practitioners call it “sluggish thyroid.” But it’s not a true thyroid condition. It’s usually a case of a dysregulated gut.

The Gut-Thyroid Axis 

When things go wrong in both the gut and thyroid, an unbalanced gut microbiome (dysbiosis) is often the common thread [28]. Dysbiosis is known to cause or be connected with [29, 30]:

• Inflammation, increased intestinal permeability (leaky gut), and altered immune system responses (remember: Hashimoto’s thyroiditis is an autoimmune disease)
• Altered activity of enzymes that impact thyroid hormone levels
• Reduced absorption of minerals that are important for the thyroid gland
• Brain fog, depression, and other cognitive issues that are similar to hypothyroid symptoms 

A Gut-Friendly Plan 

Regardless of the diagnosed hypothyroid condition, working on gut health can help improve thyroid symptoms tremendously. Probiotics, which we’ve covered already, are an important part of this, but a gut-healthy diet is vital.

There’s no single gut-health diet that is perfect for everybody, but a gut-healthy diet should generally: 

• Be anti-inflammatory
• Help keep your blood sugar balanced
• Exclude any foods that trigger gut reactions (which will be unique to each person)

Many of my hypothyroid clients do well using a Paleo diet framework, as it checks the above boxes without being overly restrictive.

Some people find that cutting down on gluten and lactose helps their hypothyroid symptoms, though the research isn’t clear one way or the other. If these or other food sensitivities are playing a significant role in gut or thyroid symptoms, a low-FODMAP diet is an evidence-based diet that may be worth trying.

Are Iodine Supplements Helpful?

Iodine is a trace mineral that we only need in tiny amounts to produce thyroid hormones [31]. When iodine levels are low in the soils used to grow crops, people can easily develop iodine deficiency, the leading cause of hypothyroid conditions. In the U.S., people are unlikely to be deficient nowadays because, even though a lot of the country has low amounts of iodine in the soil, most of us use enough iodized salt to make up for it [32].

Though it may feel right to assume that iodine would be an appropriate treatment for an underactive thyroid or symptoms that suggest it, I wouldn’t leap to supplementing with iodine supplements, like kelp. 

In fact, too much iodine can be as bad as too little. Many studies have shown that excess iodine may cause side effects and ultimately increase the overall incidence of thyroid conditions, including goiter and autoimmunity [33, 34]. And perhaps surprisingly, studies have shown that restricting iodine may actually improve thyroid function in people with hypothyroidism resulting from Hashimoto’s [35] and in those with subclinical hypothyroidism [36]. 

In short, to optimize thyroid function, food sources of iodine, like fish and dairy (or at most a low-dose iodine supplement), are probably the best way to go. And for those who already have Hashimoto’s or hypothyroidism, check with your health practitioner before increasing your iodine intake.

Thyroid Supplements Are Just One Part of the Plan

Supplements are called supplements for a reason: They are extras to the more fundamental work we all need to do to achieve or maintain good health. 

In the case of thyroid health, particularly for conditions like subclinical hypothyroidism and Hashiomoto’s, supplements can be helpful. But we can’t expect them to have much impact unless we’re also working on underlying gut health.

If, after reading this article, you still have questions about the best thyroid supplements for a specific condition or symptoms, feel free to reach out for a consultation at our clinic. My colleagues and I have also formulated a complete thyroid course that many people with lingering thyroid issues have found extremely useful. You can follow this yourself at home without needing a practitioner’s support.

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