Your Guide to Antithyroid Medication for Hyperthyroidism

Woman touching her neck

Key Points:

  • Antithyroid medications are safe and effective, even with long-term use.
  • After beginning treatment with medication, it’s important to look for the cause of your hyperthyroidism, which is often autoimmune-related. 
  • Working on gut health can not only improve thyroid health but may also allow you to reduce your antithyroid medication over time due to better absorption.
  • Supplements like selenium, L-carnitine, and vitamin D can also act as natural antithyroid medicines to complement or even replace prescription medications over time.

Antithyroid medications can safely and effectively help you manage short-term symptoms of an overactive thyroid so you can investigate what is causing your hyperthyroidism. 

In this article, we’ll discuss what hyperthyroidism is, the most common antithyroid medications, their possible side effects and safety profiles, and some alternative and complementary treatment options that could potentially replace or support pharmaceutical treatment. 

What Is Hyperthyroidism?

Hyperthyroidism occurs when the thyroid gland, a butterfly shaped gland near your throat, overproduces thyroid hormones. As an important part of the endocrine system, your thyroid regulates your metabolism, energy levels, digestion, and more. When you have too much thyroid hormone, these systems can become dysregulated. Over time, the thyroid gland itself can deteriorate. 

Hyperthyroidism is conventionally managed with either Radioactive Iodine Therapy (RAI), or with medications collectively called thionamide therapy (antithyroid drug therapy). However, there are also alternative treatment options, including L-carnitine, vitamin D, and selenium.

In the short term, it’s best to begin looking for the cause of hyperthyroidism while managing the symptoms (typically using medications). Whether one does this with pharmaceuticals or naturally is not of great concern. The important thing is to do what works. In the long term, it’s important to figure out what’s causing the hyperthyroidism. Often it’s autoimmune in nature, so finding the source of autoimmunity and treating that (the cause) is critical when it comes to achieving wellness.

Graves’ Disease

Graves’ disease, an autoimmune attack on the thyroid, is the most common cause of hyperthyroidism. One in 200 Americans has it. This makes hyperthyroidism much less common than hypothyroidism, an underactive thyroid. However, hyperthyroidism, and thyroid disease in general, is much more prevalent in women than men [1, 2]. Graves’ disease accounts for 60-80% of hyperthyroid cases [3].

Graves’ disease is caused by thyroid stimulating antibody (TSAb), which binds with thyroid stimulating hormone (TSH) receptors on thyroid cells and stimulates hormone production and growth of the thyroid gland.

Graves’ hyperthyroidism can also cause an eye disease called Graves’ ophthalmopathy [4], which affects about 25% of Graves’ disease patients [5].


Hyperthyroid symptoms include [4]:

  • Heart palpitations 
  • Nervousness or anxiety
  • Tremors 
  • Difficulty breathing 
  • Becoming easily fatigued 
  • Weight loss despite a higher appetite 
  • Diarrhea or increased GI motility 
  • Muscle weakness 
  • Heat intolerance 
  • Sweating more than usual
  • Sore throat
  • Possibly enlarged thyroid gland (goiter) 
  • Possibly tender thyroid gland.

If left untreated, hyperthyroidism can lead to a life-threatening complication called thyrotoxicosis, also called a thyrotoxic crisis or a thyroid storm. This is a pretty rare outcome, but one possible cause of thyrotoxicosis is suddenly stopping antithyroid medication, so it’s important to work with your doctor when making any adjustments to your medication regimen. 

Potential Causes Behind Hyperthyroidism

There are a few possible causes of hyperthyroidism, including: 

  • Autoimmunity, as with Graves’ disease. 
  • Acute infection, such as an upper respiratory infection that can cause inflammation in the thyroid gland [4]
  • Iodine-induced hyperthyroidism, which can be caused by iodine-containing medications [4]
  • Postpartum thyroiditis, where the thyroid becomes inflamed after birth, sending a lot of thyroid hormones into the bloodstream [6]

Especially in young people, autoimmunity is the most likely culprit. Autoimmunity in general has numerous different causes, such as gut infections, nutrient deficiencies, psychological stress, among others. It’s important to work with your doctor to investigate these potential causes for long-term hyperthyroid treatment, even if you take antithyroid medication. 

Antithyroid medication: pills and capsules

What Are the Different Kinds of Antithyroid Medications?

There are two conventional medication options for hyperthyroidism, which are: 

  • Methimazole (MMI)
  • Propylthiouracil (PTU)

Methimazole and propylthiouracil are the two main drugs in the thionamide class. These medications are typically used for 18-24 months, after which they are discontinued in the hope of achieving remission [7].

However, research has shown that these medications can be used long-term, and may be more effective when used for 5-10 years [7, 8, 9, 10].

Other Medical Treatment Options for Hyperthyroidism

Radioactive iodine therapy (RAI) destroys the thyroid tissue to decrease production of thyroid hormones and is considered the preferred treatment method for Graves’ patients in the U.S. This is usually a single-dose treatment administered orally (as a pill or liquid). It requires patients to avoid close contact with others in the few days following the treatment due to radiation exposure. After the therapy is administered, endocrinologists will follow up with patients every 4-6 weeks to evaluate hyperthyroid symptoms and hormone levels. 

RAI is generally well tolerated but can be problematic for people with heart disease. It’s also contraindicated for nursing or pregnant women [4].

There is also a thyroid surgery option, a subtotal thyroidectomy, or removal of part of the thyroid gland. This requires a substantial decrease in thyroid hormone levels first to avoid complications during surgery. Ultimately, it reduces T4 hormone secretion to treat hyperthyroidism, but this can also lead to hypothyroidism. 

Although subtotal thyroidectomy is a generally safe procedure, possible complications include accidental removal of parathyroid gland(s) and accidental injury to the recurrent laryngeal nerve. As with any surgery, this is a last resort for treatment of hyperthyroidism.. 

Antithyroid Drug Side Effects

There are many possible side effects with antithyroid medications, but they are typically manageable and low risk. 

Methimazole (brand names: Northyx, Tapazole) side effects include: 

  • Agranulocytosis: a type of white blood cell deficiency causing increased susceptibility to infection
    • Symptoms include fever, chills, rapidly progressive infection, and sore throat
  • Aplastic anemia (occurs when the body can’t produce enough red blood cells)
  • Skin reactions including rash and pigmentation
  • Hepatotoxicity 
  • Salivary gland swelling
  • Neuritis (nerve inflammation)
  • Vertigo [11]

Propylthiouracil (brand name: Propacil) side effects include: 

  • Agranulocytosis
  • Aplastic anemia
  • Skin reactions
  • Hepatitis
  • Drowsiness
  • Fever
  • Headache
  • Goiter (an enlargement of the thyroid gland)
  • Weight gain
  • Constipation
  • Loss of taste [12]

Are Antithyroid Medications Safe? 

When taking any medication, it’s important to be mindful of potential side effects, but there usually isn’t cause for alarm. Research shows that antithyroid medication is generally safe and effective for symptom relief, even with long term use.

A systematic review and meta-analysis of six clinical trials found evidence that long-term antithyroid drug treatment induced remission in 61% of adults and 53% of children with hyperthyroidism. Although other potential causes for remission were not explored in the studies analyzed, the study concluded that long-term use of antithyroid medications is effective and safe, especially in adults [8].

A randomized clinical trial including 302 Graves’ disease patients found that low-dose methimazole taken long term both safely and effectively treated Graves’ hyperthyroidism. Specifically, those who took low-dose methimazole for 5-10 years had only a 15% relapse rate [7].

In contrast, those who took methimazole for 18-24 months and then discontinued had a relapse rate of 53%. Some adverse effects occurred in the first 18 months of treatment and then subsided thereafter. They included skin rash in 14 (4.6% of) patients and elevated liver enzymes in 2 (0.7% of) patients [7].

Comparing RAI and Antithyroid Drug Safety

When we compare RAI to long-term low-dose methimazole drug therapy, the research supports methimazole as a lower risk and more effective treatment option than RAI. 

One randomized clinical trial of 239 patients with diffuse toxic goiter and recurrent hyperthyroidism found that, after 14 years of followup, “Long-term MMI [methimazole] 

treatment was superior to RAI [radioactive iodine] therapy in patients with diffuse toxic goiter when mood, cognition, cardiac function, and occurrence of thyroid dysfunction were compared” [10].

Another randomized clinical trial including 107 patients with toxic multinodular goiter in Iran found that long-term low-dose methimazole for 5-8 years was safe and effective for treating TMNG and better than radioactive iodine (RAI) therapy [13].

Improving Gut Health for Better Thyroid Function

We know that gut health is intricately linked to the outcome of any autoimmune condition, and this includes thyroid conditions like Hashimoto’s disease and Graves’ disease. 

When the gut is inflamed, the microbiome is imbalanced, and the gut lining can’t absorb nutrients properly, inflammation becomes systemic. It can trigger the immune system to attack the body’s own tissues, which is also called an autoimmune attack. For example, one systematic review and meta-analysis found that there was a significant association between H. pylori infection and Graves’ disease [14].

We also know that the gut and the thyroid are connected, and many thyroid disease symptoms can also be gut-related symptoms. Thyroid hormones also help control gut function and motility, so an impaired thyroid can in turn impair gut health and vice versa in a vicious cycle.

It stands to reason that improving your gut health can both reduce inflammation that may be contributing to hyperthyroidism and improve the gut’s ability to absorb medications, perhaps allowing you to reduce your dose of antithyroid medication.

Antithyroid Medication Alternatives and Complementary Treatments

Woman holding a heart cutout

Although antithyroid medications are generally safe and have a low risk of severe side effects, there are natural remedies that may be able to either replace or complement antithyroid drug therapy ​for the treatment of Graves’ disease or hyperthyroidism.


There is some evidence suggesting that a gluten-free diet may be helpful for hyperthyroidism if it is autoimmune in nature (Graves’ disease). A 2019 nonrandomized controlled trial with 34 women with Hashimoto’s disease (autoimmune hypothyroidism) found that a gluten-free diet reduced their thyroid antibodies [15]. A gene associated with Graves’ disease (CTLA-4) [16] is also associated with celiac disease [17, 18], indicating that gluten sensitivity may be a factor for some Graves’ patients.

More generally, it’s likely that an anti-inflammatory diet that is high in antioxidants will be helpful in addressing hyperthyroidism [19].

A 2020 observational study including 324 patients with normal thyroid hormones and obesity found that those who more closely followed a Mediterranean diet had lower T3 and T4 levels. Those who ate at least four spoonfuls of extra-virgin olive oil daily had lower free T4 levels, and if they also ate two servings of vegetables per day, they had lower free T3 levels, too. 

Overall, in overweight/obese people with normal thyroid levels, closely following a Mediterranean diet was associated with slightly reduced thyroid function, but still within reference range [20]. This is not conclusive evidence for the Mediterranean diet in treating hyperthyroidism, but using a general anti-inflammatory diet (such as a Mediterranean or Paleo diet) is likely to be helpful as a foundational health strategy.

Antithyroid medication: raw sea bass surrounded by vegetables


L-Carnitine, an amino acid, has been shown to prevent or reduce symptoms of hyperthyroidism. It works quickly, has very low risk of side effects, and is safe for pregnant women to take [21].

A randomized clinical trial including 50 women with temporarily induced hyperthyroidism found that L-Carnitine supplementation improved hyperthyroid symptoms like weakness and fatigue, nervousness, shortness of breath, tremors and insomnia. Comparatively, a placebo worsened these symptoms [21]. 

This research suggests that L-Carnitine may be a valuable replacement or adjunct therapy to antithyroid medications. 


Selenium, a trace mineral integral for normal thyroid function, may be beneficial as an adjunct treatment to antithyroid medications, including methimazole. Multiple studies have shown that selenium supplementation alongside MMI and radioactive iodine therapy improved treatment outcomes for hyperthyroid patients [22, 23].

Other studies have shown that patients with Graves’ disease were more likely to have lower selenium levels [24] and hyperthyroid patients with higher levels of serum selenium were less likely to relapse after treatment [25].

However, some studies did not show decreased thyroid antibodies after selenium supplementation [26, 27]. So, work with your doctor to check your selenium levels and decide whether supplementation is a good option for you. 

Vitamin D

A systematic review and meta-analysis including 3,716 participants found evidence that patients with Graves’ disease were more likely than healthy controls to have vitamin D deficiency. This indicates that low vitamin D status may increase the risk of Graves’ disease [28].

Another SR/MA of six randomized clinical trials found moderate quality evidence that vitamin D supplementation may reduce antibodies to thyroid peroxidase (TPO) and thyroglobulin (Tg), both of which are possible markers of autoimmune thyroiditis (hyper or hypothyroidism) [29].

Again, vitamin D supplementation has a very low risk of side effects, so it’s worth looking into as a hyperthyroid therapy. 


Though the evidence is still limited when it comes to probiotics for hyperthyroidism specifically, probiotics may help to improve thyroid health, seal up a leaky gut, and lower inflammation. 

A 2020 literature review explained that gut dysbiosis has been found in autoimmune thyroid disorders, and the composition of gut microbes can affect the availability of nutrients, such as iodine, iron, copper, selenium, zinc, and vitamin D, for thyroid function. Limited research suggests that probiotics may help stabilize thyroid function, hormone levels, and trace element levels, such as selenium, zinc, and copper [30].

Antithyroid medication: little girl hugging her mom

The Bottom Line on Antithyroid Medication

It’s important to get hyperthyroid symptoms under control quickly, and antithyroid medications are a relatively safe and effective way to do so. Thionamide medications like methimazole have a low side-effect profile and are often more effective when used long term. You don’t have to fear these medications, and they can be an effective solution while you investigate the root cause of your hyperthyroid symptoms. 

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