graves’ disease medication

Methimazole is the first-line medication for Graves’ disease in most of the world, and it works by slowing down the thyroid’s ability to produce hormones. A second antithyroid drug, propylthiouracil (PTU), serves as the backup when methimazole cannot be used. Beyond these two, beta-blockers handle the racing heart and tremor while the antithyroid drugs take effect, and newer treatments are emerging for complications like thyroid eye disease. The medication landscape for Graves’ is broader and more nuanced than many people realize, with decisions shaped by how severe the disease is, whether you are pregnant, how old you are, and how your body responds over time.

How Antithyroid Drugs Work

Methimazole and PTU both target the thyroid gland, but they do it differently. Methimazole blocks the enzyme system inside thyroid cells that attaches iodine to the building blocks of thyroid hormone. By disrupting that step, it reduces the output of the hormones T3 and T4. PTU does the same thing but adds a second trick: it also blocks the conversion of T4 into the more active T3 in tissues outside the thyroid.¹ That extra action sounds like it would make PTU the stronger drug, but in practice methimazole is more potent, acts faster, and can be taken once daily, which makes it easier to stick with.

There is also a less-discussed dimension to how these drugs work. Research going back decades has shown that methimazole and its relative carbimazole appear to dampen the autoimmune process itself, not just the hormone output. In treated patients, levels of the antibodies that drive Graves’ disease tend to fall during therapy. Lab studies found that methimazole could inhibit thyroid-antibody production in cultured immune cells, and because the drug concentrates in thyroid tissue, it may act locally to suppress antibody synthesis right where the immune attack is happening.² Later work confirmed that methimazole therapy shifts the balance of immune cell subtypes in ways that favor suppression of autoantibody production.³ This immunomodulatory effect is part of why antithyroid drugs can sometimes produce lasting remission rather than just temporary hormone control.

Methimazole Versus PTU

Head-to-head comparisons consistently favor methimazole. In a trial of 240 patients, a standard dose of methimazole normalized thyroid hormone levels in about 97% of patients at 12 weeks, compared with roughly 78% on PTU. For people with mild or moderate disease, a lower dose of methimazole performed nearly as well, while PTU lagged behind, particularly in severe cases.⁴ Side effects were also more common with PTU, especially mild liver problems. The same study concluded that PTU is not recommended as initial treatment.

So why does PTU still exist? It fills two critical niches. During the first trimester of pregnancy, methimazole carries a somewhat higher risk of certain birth defects, so PTU is preferred for those early weeks. And in thyroid storm, the life-threatening extreme of hyperthyroidism, PTU’s ability to block T4-to-T3 conversion throughout the body provides an advantage when you need every possible brake applied at once. Outside those situations, methimazole is the standard choice.

Beta-Blockers for Symptom Relief

Antithyroid drugs take several weeks to bring hormone levels down. In the meantime, the symptoms of Graves’ can be miserable: a pounding heart, trembling hands, anxiety, heat intolerance, and insomnia. Beta-blockers step in to cover this gap. They do not affect hormone production at all. Instead, they block the receptors that adrenaline uses to speed up the heart and heighten the nervous system’s activity.

Propranolol is the most commonly prescribed beta-blocker for this purpose because it crosses into the brain more readily, helping with the anxiety and neuropsychiatric symptoms that bother many Graves’ patients. Other beta-blockers that act mainly on the heart are effective for controlling the fast pulse rate but do less for the mental symptoms.⁵ Beta-blockers are a temporary bridge, typically tapered off once antithyroid drugs bring hormone levels into the normal range.

Dose Titration Versus Block and Replace

There are two main strategies for giving antithyroid drugs. In dose titration, you start with enough medication to control the overactive thyroid and then gradually reduce the dose to the minimum that keeps hormones in the normal range. In block and replace, you give a high fixed dose that shuts down the thyroid entirely and then add a daily levothyroxine tablet to replace what the body needs. The logic of block and replace is that it avoids the seesaw of dose adjustments, but it means taking two drugs instead of one.

A Cochrane review pooling data from multiple trials found no meaningful difference in relapse rates between the two approaches: roughly half of patients relapsed with either strategy after stopping treatment.⁶ What did differ was the side-effect profile. Skin rashes were about three times more common with block and replace, and more patients in that group had to stop treatment because of adverse effects. A trial in young patients with thyrotoxicosis similarly found no advantage to block and replace over titration in keeping thyroid levels stable, and all serious drug reactions involving dangerously low white blood cell counts occurred in the block-and-replace arm.⁷ Dose titration is therefore the more widely recommended approach, though block and replace still has a role in patients whose hormone levels swing unpredictably.

How Long You Stay on Medication and the Relapse Problem

The traditional course of antithyroid drug therapy lasts about 12 to 18 months, after which you stop the medication and hope remission holds. Unfortunately, for many people it does not. A randomized trial found that among patients treated with a conventional course and then taken off methimazole, about 56% relapsed. In contrast, patients who stayed on long-term methimazole had a relapse rate of only 17%.⁸ Extending treatment with low-dose methimazole to five or even ten years has been shown to safely and effectively keep patients in remission far more often than the standard short course.⁹

Continuing a small daily dose of methimazole, typically 2.5 to 5 milligrams, in patients who have achieved stable normal thyroid levels is effective at preventing recurrence for as long as the medication is taken.¹⁰ This approach is gaining traction as doctors and patients weigh the inconvenience of a daily pill against the risks of radioactive iodine or surgery. A literature review concluded that long-term antithyroid drug therapy delivers stable thyroid function with minimal complications, low cost, and better quality-of-life outcomes compared with the permanent alternatives.¹¹

Predicting Who Will Relapse

Not everyone who stops antithyroid drugs relapses, and researchers have been working to figure out who is at highest risk. The antibodies that cause Graves’ disease, known as thyroid-stimulating antibodies or TRAb, are the best-studied predictor. One study found that patients who still tested positive for thyroid-stimulating antibodies at the time they stopped medication relapsed 67% of the time, compared with only 17% of those who had become negative.¹²

Antibody levels at the very start of treatment also matter. Patients who begin with high TRAb titers have about 1.7 times the odds of relapsing compared with those who start with low levels, even after accounting for other risk factors. Analysis suggests there is a threshold effect: above a certain antibody level at diagnosis, the risk of relapse climbs steeply and then levels off.¹³ In practical terms, if your antibody levels remain stubbornly elevated during treatment, your doctor may discuss either extending drug therapy or considering definitive treatment rather than stopping and gambling on remission.

Side Effects Worth Knowing About

Most people tolerate antithyroid drugs well. Minor side effects like skin rash, joint pain, and stomach upset affect a moderate fraction of patients and often resolve with a dose reduction or a switch between drugs. The side effects that genuinely worry doctors are rare but serious.

The most feared is agranulocytosis, a sudden and dangerous drop in white blood cells that leaves you vulnerable to overwhelming infection. It typically announces itself with high fever, severe sore throat, and sometimes diarrhea.¹⁴ It can occur with either methimazole or PTU, and if it happens with one drug, switching to the other is not guaranteed to be safe; in a case series, agranulocytosis persisted in patients who were switched from PTU to methimazole.¹⁵ Anyone on antithyroid drugs who develops a sudden fever or sore throat should have a blood count checked urgently.

Liver injury is the other major concern, and the pattern differs between the two drugs. A large population-based study found that methimazole (and its relative carbimazole) caused hepatitis-type liver inflammation at a higher rate than PTU. However, PTU was more likely to cause acute liver failure, which is far more dangerous. High-dose methimazole carried the greatest hepatitis risk, nearly five times that of PTU.¹⁶ In children specifically, PTU has been linked to severe liver injury at disproportionately high rates, while methimazole’s liver effects in younger patients are much milder.¹⁷ This is one reason PTU is now strongly discouraged in children.

Pregnancy and Graves’ Disease Medication

Managing Graves’ disease during pregnancy requires careful drug selection because both methimazole and PTU can cross the placenta and affect the developing baby. A large meta-analysis of observational studies found that methimazole or carbimazole use during pregnancy was associated with roughly 18 additional birth defects per 1,000 pregnancies compared with unexposed women, while PTU was linked to about 10 additional cases per 1,000. Exposure to both drugs sequentially during pregnancy carried the highest excess risk, about 33 extra cases per 1,000.¹⁸ Another meta-analysis confirmed that the odds of birth defects in the first trimester were higher with methimazole than with PTU.¹⁹

The current standard practice is to use PTU during the first trimester, when the risk of methimazole-related birth defects is highest, and then switch to methimazole for the remainder of pregnancy to avoid PTU’s liver toxicity with prolonged use. Some smaller studies have reported reassuring results with methimazole throughout pregnancy, with no increase in birth defects or miscarriage compared to the general population.²⁰ But the weight of evidence from larger studies supports the switch strategy, and most guidelines follow it. Untreated hyperthyroidism itself also raises the risk of birth defects, so stopping medication entirely is not the answer.

Children and Adolescents

Graves’ disease in children is less common than in adults but harder to manage with medication alone. Methimazole is the only antithyroid drug recommended for children because of PTU’s severe liver toxicity in younger patients. Remission rates after a standard two-year course are lower than in adults: a systematic review of nearly 3,000 pediatric patients found an overall remission rate of about 29%.²¹ Longer treatment courses appear to help. The same review found remission rates climbed from about 24% after two years of treatment to roughly 44% after five to six years, and a single long-duration study reported 75% remission after nine years. Side effects in the reviewed studies occurred in about 18% of patients, though serious reactions were rare at around 1%.

These numbers mean that the majority of children treated for two years will relapse and eventually need either extended medication or definitive treatment with surgery. Radioactive iodine is used less often in young children due to concerns about radiation exposure in growing tissue, so thyroidectomy tends to be the preferred definitive option when drugs fail.

When Medication Alone Is Not Enough

Antithyroid drugs are not the only option for Graves’ disease. Radioactive iodine (RAI) and thyroid surgery are the two “definitive” treatments, meaning they aim to permanently resolve the overactive thyroid, usually by destroying or removing it. A nationwide population study found that the success rate of antithyroid drugs was about 50%, compared with 93% for RAI and 99% for surgery. Among patients who stayed on antithyroid drugs for at least a year before being evaluated, the failure rate dropped to about 25%.²² Side effects were most common with surgery (about 24% of patients) but were largely transient, while RAI had the lowest adverse-event rate. In a direct comparison, RAI achieved an overall success rate of about 90% including repeat doses, and no surgical patients had Graves’ recurrence, though operative complications were higher.²³

The trade-off with both definitive treatments is that most patients become permanently hypothyroid and need daily levothyroxine for the rest of their lives. Some patients and doctors now view long-term low-dose methimazole as preferable to this outcome, especially when the disease is well-controlled and side effects are absent.

Iodine Intake and Drug Effectiveness

What you eat can influence how well antithyroid drugs work, specifically how much iodine is in your diet. A systematic review found that adequate iodine intake, not too little and not too much, was associated with lower relapse rates and better drug effectiveness compared with iodine deficiency or excess.²⁴ A clinical study specifically testing iodine supplementation versus iodine restriction during antithyroid drug therapy found that the group with adequate iodine supplementation had a recurrence rate of about 36%, compared with roughly 46% in the iodine-restricted group.²⁵

This runs counter to the common advice patients receive to avoid iodine entirely. While large amounts of iodine, from kelp supplements or iodine-containing contrast dyes, can worsen hyperthyroidism, moderate daily iodine from an ordinary diet may actually support better outcomes. Strict iodine restriction does not help and might hurt. The evidence here is still evolving, but it suggests that the old blanket recommendation to slash dietary iodine may have been too aggressive.

Thyroid Eye Disease and Teprotumumab

Thyroid eye disease, the bulging eyes and double vision that can accompany Graves’, has historically been one of the more frustrating complications to treat medically. Antithyroid drugs help by stabilizing thyroid function, and radioactive iodine can sometimes worsen eye symptoms. The landscape changed significantly with the approval of teprotumumab, a biologic drug that targets a growth factor receptor involved in the inflammation and tissue expansion behind the eyes.

In its pivotal trial, about 83% of patients treated with teprotumumab had a meaningful reduction in eye bulging at 24 weeks, compared with 10% on placebo. The benefit extended to double vision, inflammation scores, and quality of life, all significantly better than placebo.²⁶ An earlier phase 2 trial had already shown that about 69% of teprotumumab patients responded versus 20% on placebo, with effects visible as early as six weeks into treatment.²⁷ Teprotumumab is expensive and given by intravenous infusion, but it represents the first medication to directly address the underlying mechanism of thyroid eye disease rather than just suppressing inflammation with steroids.

Thyroid Storm

At the extreme end of the severity spectrum, thyroid storm is a medical emergency where the body is overwhelmed by thyroid hormones. Without treatment, mortality has been estimated at 80% to 100%; with aggressive treatment it drops to between 10% and 50%.²⁸ Treatment typically involves high-dose PTU (for its dual mechanism of blocking hormone synthesis and peripheral T4-to-T3 conversion), intravenous beta-blockers, corticosteroids, and iodine solutions given in a specific sequence to shut down hormone release. Thyroid storm is rare, but it underscores why Graves’ disease requires ongoing monitoring and why medication adherence matters: most cases are triggered by stopping antithyroid drugs abruptly, untreated infection, or surgery in an uncontrolled hyperthyroid patient.

Experimental Therapies on the Horizon

The medications available today are all variations on the same basic approaches: suppress hormone production, manage symptoms, or destroy the gland. None of them directly fix the autoimmune error that causes Graves’ disease. Researchers are now working on therapies that could do exactly that. One promising avenue involves blocking a receptor called FcRn, which extends the lifespan of antibodies in the bloodstream. Blocking FcRn would accelerate the clearance of the thyroid-stimulating antibodies that drive the disease, potentially shutting it down at its source.²⁹ Other strategies are targeting the TSH receptor itself or specific immune pathways upstream of antibody production.³⁰ None of these have reached routine clinical use yet, but the field is moving closer to treatments that address the root cause rather than mopping up its downstream effects.

1
PubMed Central. The efficiency and safety of methimazole and propylthiouracil in hyperthyroidism: A meta-analysis of randomized controlled trials ↩︎
2
PubMed. Carbimazole and the autoimmune response in Graves’ disease ↩︎
3
PubMed. Induction of circulating activated suppressor-like T cells by methimazole therapy for Graves’ disease ↩︎
4
PubMed. Comparison of methimazole and propylthiouracil in patients with hyperthyroidism caused by Graves’ disease ↩︎
5
PubMed Central. The Therapeutic Potential of Propranolol and Other Beta-Blockers in Hyperthyroidism ↩︎
6
Cochrane Database of Systematic Reviews. Dose, regimen and duration of antithyroid drug therapy for Graves’ disease hyperthyroidism ↩︎
7
European Journal of Endocrinology. Randomised trial of block and replace vs dose titration thionamide in young people with thyrotoxicosis ↩︎
8
PubMed. Risk of recurrence at the time of withdrawal of short- or long-term methimazole therapy in patients with Graves’ hyperthyroidism: a randomized trial and a risk-scoring model ↩︎
9
PubMed. Increased Remission Rates After Long-Term Methimazole Therapy in Patients with Graves’ Disease: Results of a Randomized Clinical Trial ↩︎
10
PubMed Central. Benefits of Long-Term Continuation of Low-Dose Methimazole Therapy in the Prevention of Recurrent Hyperthyroidism in Graves’ Hyperthyroid Patients: A Randomized Prospective Controlled Study ↩︎
11
PubMed. Comparison of long-term antithyroid drugs versus radioactive iodine or surgery for Graves’ disease: A review of the literature ↩︎
12
PubMed Central. Usefulness of Measuring Thyroid Stimulating Antibody at the Time of Antithyroid Drug Withdrawal for Predicting Relapse of Graves Disease ↩︎
13
Endocrinology and Metabolism. High TRAb Titer at Diagnosis Predicts Persistent Positivity and Relapse in Graves’ Disease after Prolonged Antithyroid Therapy ↩︎
14
PubMed Central. Antithyroid Drug-Induced Agranulocytosis: State of the Art on Diagnosis and Management ↩︎
15
PubMed. Antithyroid drug-induced agranulocytosis ↩︎
16
PubMed Central. Antithyroid drug-related hepatotoxicity in hyperthyroidism patients: a population-based cohort study ↩︎
17
The Journal of Clinical Endocrinology & Metabolism. Dissimilar Hepatotoxicity Profiles of Propylthiouracil and Methimazole in Children ↩︎
18
PubMed Central. Antithyroid drug use during pregnancy and the risk of birth defects in offspring: systematic review and meta-analysis of observational studies with methodological considerations ↩︎
19
Endocrine Practice. Side Effects of PTU and MMI in the Treatment of Hyperthyroidism: A Systematic Review and Meta-Analysis ↩︎
20
PubMed. Pregnancy outcome in women treated with methimazole or propylthiouracil during pregnancy ↩︎
21
PubMed. Methimazole-induced remission rates in pediatric Graves’ disease: a systematic review ↩︎
22
PubMed. Patterns of Use, Efficacy, and Safety of Treatment Options for Patients with Graves’ Disease: A Nationwide Population-Based Study ↩︎
23
PubMed Central. Comparative analysis of radioactive iodine versus thyroidectomy for definitive treatment of Graves disease ↩︎
24
PubMed Central. Effect of iodine nutritional status on the recurrence of hyperthyroidism and antithyroid drug efficacy in adult patients with Graves’ disease: a systemic review ↩︎
25
PubMed. Optimal iodine supplementation during antithyroid drug therapy for Graves’ disease is associated with lower recurrence rates than iodine restriction ↩︎
26
PubMed. Teprotumumab for the Treatment of Active Thyroid Eye Disease ↩︎
27
PubMed Central. Teprotumumab for Thyroid-Associated Ophthalmopathy ↩︎
28
PubMed Central. Acute and emergency care for thyrotoxicosis and thyroid storm ↩︎
29
Endocrine Reviews. New Therapeutic Horizons for Graves’ Hyperthyroidism ↩︎
30
PubMed Central. Graves’ Disease: Is It Time for Targeted Therapy? A Narrative Review ↩︎