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Supplements for Graves' Disease and an Overactive Thyroid: What to Avoid and What Trials Show

Supplements don't treat Graves' disease; your endocrinologist does, with antithyroid medicine, radioactive iodine or surgery. Avoid kelp and other iodine supplements, ashwagandha and "thyroid support" pills, which can make an overactive thyroid worse, and mention biotin before blood tests. Selenium has the best case: for mild Graves' eye disease it helped in a trial of 159 people (grade B), but it did not raise remission rates in a trial of 430 (grade B).

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Supplements don't treat Graves' disease; your endocrinologist does. Graves' disease is an autoimmune condition: the immune system makes antibodies that push the thyroid gland, at the front of the neck, to make too much thyroid hormone. It is the most common cause of a lasting overactive thyroid (hyperthyroidism) in adults (Burch 2015). Signs include a fast heartbeat, shaking hands, weight loss and heat intolerance, and many people also get eye problems (MedlinePlus).

The three treatments are antithyroid medicine (methimazole or carbimazole, or propylthiouracil), radioactive iodine and surgery. A 12- to 18-month course of antithyroid medicine leads to remission in about half of people (Burch 2015). This guide covers adults and gives no medicine doses. Keep taking your prescribed treatment; don't stop, skip or swap it for a supplement.

The short version

  • Kelp, iodine and "thyroid support" pills can make an overactive thyroid worse. Kelp products have set off hyperthyroidism in case reports, and 9 of 10 thyroid supplements tested held real thyroid hormone. Grade C (harm) (Kang 2013; Müssig 2006).
  • Ashwagandha has been linked to thyrotoxicosis (too much thyroid hormone in the blood) in case reports, and NCCIH does not recommend it for anyone with a thyroid disorder. Grade D (harm) (van der Hooft 2005; NCCIH).
  • Biotin in hair, skin and nail products can make thyroid blood tests look like Graves' disease when it isn't (Elston 2016).
  • Selenium for mild Graves' eye disease: in a trial of 159 people, those on selenium for 6 months rated their eye-related quality of life higher, and their eyes worsened less, than those on a dummy pill; later trials agree less. Grade B (Marcocci 2011; Kostadinov 2026).
  • Selenium for the overactive thyroid itself: blood hormone levels fell a little faster for a few months, but remission rates did not change in 430 people. Grade B (Zheng 2018; Cramon 2026).
  • Vitamin D did not help remission or bone density in people newly treated for Graves' disease, and muscle strength recovered less on it. Grade C (Grove-Laugesen 2023; Grove-Laugesen 2020).
SupplementWhat trials foundSize of effectGrade
Kelp and iodine supplementsCan set off or worsen an overactive thyroidCase reports and reviewsC (harm)
AshwagandhaLinked to thyrotoxicosisCase reportsD (harm)
Selenium, Graves' eye disease (vs dummy pill or no selenium)Better eye quality of life in one trial in mild disease; pooled trials of mixed severity show a small drop in eye inflammationActivity score about 1 point lower (5 trials, 303 people)B
Selenium added to antithyroid medicineHormone levels fell a little faster at 3 to 6 months; no more remissionsNo change in remission (430 people)B
L-carnitine (50 women on high-dose thyroid hormone tablets, vs dummy pill)Fewer overactive-thyroid symptomsNot given as one numberC
Vitamin D, newly treated Graves' (vs dummy pill)No help with remission or bone density; muscle strength recovered lessRemission not reached: 42% vs 32% (not statistically clear)C

Which supplements should you avoid with Graves' disease?

Kelp, seaweed and iodine supplements (grade C, harm). Iodine is the raw material for thyroid hormone, and a sudden large load can tip a susceptible thyroid into overdrive (Sohn 2024). A 39-year-old woman with a goiter (an enlarged thyroid) became hyperthyroid after 4 weeks of a herbal tea containing kelp (Müssig 2006), and a 45-year-old woman with no history of thyroid problems became hyperthyroid on a diet product containing kelp (Di Matola 2014). NIH says people with autoimmune thyroid disease can react to iodine amounts that are safe for others, and high iodine on top of antithyroid medicine can push thyroid levels too low (NIH ODS). Kelp and other seaweed products are the usual culprits, and many multivitamins also contain iodine, so show your endocrinologist the label.

"Thyroid support" and glandular pills. When 10 "thyroid support" supplements were bought and tested, 9 held T3 (the active thyroid hormone) and 5 held T4; at the label dose, some delivered more thyroid hormone than common prescription doses (Kang 2013). With an overactive thyroid, that adds fuel.

Ashwagandha (grade D, harm). A 32-year-old woman developed thyrotoxicosis after raising her dose of ashwagandha capsules, and it cleared when she stopped (van der Hooft 2005). In another report, a woman aged 73 who had used it for 2 years for an underactive thyroid came to hospital with a racing heart rhythm (supraventricular tachycardia) (Kamal 2022). A man aged 47 developed painless thyroid inflammation 2 months after starting it (Hayashi 2024). NCCIH lists thyroid disorders among the conditions for which ashwagandha is not recommended, and says a number of cases, though rare, link it to liver injury (NCCIH). It turns up in many stress and sleep blends.

Shilajit. No studies have tested it in people with an overactive thyroid; check any blend's label for kelp, iodine or ashwagandha.

Biotin before blood tests. Biotin in moderate to high doses can make some lab tests read falsely high or falsely low. In one report a patient's thyroid results looked like Graves' disease, then went back to normal after biotin was stopped, far faster than real thyroid hormone could have cleared (Elston 2016). The FDA warns that biotin also affects other tests, most dangerously the troponin test used to spot heart attacks (FDA). Tell whoever orders your blood test if you take it; see does biotin affect thyroid tests?.

Does selenium help Graves' eye disease?

Grade B: probably a little, for mild disease, most clearly where people are short of selenium. Graves' eye disease (thyroid eye disease, or Graves' orbitopathy) causes gritty, swollen or bulging eyes. In a double-blind trial, people with mild eye disease (159 in all) took selenium (100 mcg twice a day by mouth), an anti-inflammatory drug or a dummy pill for 6 months. Only selenium beat the dummy pill: eye-related quality of life was better and the eye disease progressed less, results at 12 months agreed, and no side effects were seen (Marcocci 2011). For mild eye disease that is still active, Europe's thyroid eye disease guideline says that tackling risk factors, treating the eyes locally and taking selenium (in areas where people are short of it) are usually enough (EUGOGO 2021).

Later trials agree less. In an area where people get enough selenium, an open-label trial in 84 people with mild to moderate eye disease, with no dummy pill, that gave selenium together with B vitamins found quality of life no better than without them after 6 months, though more people felt better at 3 months (Ahn 2025). Pooling 5 trials (303 people) against a dummy pill or no selenium, in people with different selenium levels and disease severity (including that selenium plus B vitamin trial and a trial in inactive moderate to severe eye disease), a 2026 review found the eye inflammation score about 1 point lower, with no clear change in vision, eyelid opening or quality of life, and urged caution because the trials were few and small (Kostadinov 2026). Moderate to severe eye disease is treated with prescribed medicines, not supplements. Radioactive iodine has been linked to new or worse eye disease in about 15% to 20% of people treated with it (Burch 2015), so mention any eye symptoms before choosing a treatment.

Upper limit for adults: 400 mcg a day of selenium from all sources, because more can cause hair loss and brittle or lost nails; take more only with blood tests or your clinician's advice (NIH ODS; check your stack). Europe's food safety agency set a lower limit, 255 mcg. Harms can show up below the limit too: in long cancer-prevention trials, selenium tablets went with slightly more type 2 diabetes; the biggest of them also saw more hair loss and skin rashes (Vinceti 2018). Brazil nuts are very high in selenium, so count them.

Does selenium help an overactive thyroid?

Grade B: it nudges hormone levels for a few months but doesn't change remission. Across 10 trials (796 people) that added selenium to methimazole, free T4 and free T3 (the thyroid hormones in the blood) were a little lower at 3 and 6 months, but not at 9 months. Only 2 of those trials used a dummy pill; most compared selenium plus methimazole with methimazole alone (Zheng 2018). In the largest trial, 430 people with newly found Graves' disease took 200 mcg of selenium (half the upper limit) or a dummy pill a day alongside antithyroid medicine for 2 to 2.5 years: remission, quality of life and antibody levels were no different (Cramon 2026). A smaller blinded trial agreed: response and relapse rates were similar (Kahaly 2017).

Does L-carnitine help hyperthyroid symptoms?

Grade C: one small trial, not in Graves' disease. L-carnitine is a nutrient that may stop thyroid hormone from reaching the nucleus of cells, where it acts. In a 6-month double-blind trial, 50 women kept on high doses of thyroid hormone tablets took 2 or 4 g of L-carnitine a day or a dummy pill for parts of the trial; carnitine reversed or prevented the rise in nine overactive-thyroid symptoms, and bone density tended to rise (Benvenga 2001). Because it works against thyroid hormone, ask your endocrinologist first if you later take levothyroxine after radioactive iodine or surgery. A 2025 open-label trial in 60 people newly diagnosed with Graves' disease, with no dummy pill, added a carnitine and selenium combination to methimazole: hormone levels returned to normal no faster and overall symptoms were similar, though antibodies cleared sooner, less methimazole was needed and more people went into remission. The maker supplied the product, and the combination makes it impossible to say which ingredient did what (Rossi 2025). Carnitine has no set upper limit, but about 3 g a day can cause nausea, vomiting, belly cramps, diarrhoea and a fishy body odour (NIH ODS).

Should you take vitamin D with Graves' disease?

Grade C: not to help the Graves' disease. In DAGMAR, a double-blind trial in 278 adults newly diagnosed with Graves' disease and taking antithyroid medicine, vitamin D (70 mcg, or 2,800 IU, a day) did not improve remission: 42% failed to reach or keep remission against 32% on a dummy pill, a gap that was not statistically clear (Grove-Laugesen 2023). In people newly diagnosed with Graves' disease, given the same vitamin D dose or a dummy pill alongside antithyroid medicine, muscle strength recovered less on vitamin D over 9 months, and thyroid-related quality of life improved significantly less (Grove-Laugesen 2020), and bone density did not improve, though it recovered with antithyroid treatment itself (Grove-Laugesen 2024). If testing shows your vitamin D is low, your clinician can treat that. Upper limit for adults: 4,000 IU (100 mcg) a day of vitamin D, since more can cause high blood calcium; take more only with blood tests or your clinician's advice (NIH ODS).

Does calcium help before thyroid surgery?

Grade C: it may cut tingling from low calcium afterwards; your surgical team decides. Removing the thyroid can disturb the nearby glands that control calcium. In a study of 83 people with Graves' disease having their thyroid removed, numbness and tingling afterwards affected 9% of those given calcium beforehand against 26% of an earlier group who were not; the groups were not randomized (Oltmann 2015). A review found 9 trials that gave calcium, vitamin D or the two together before thyroid removal for any reason; 7 of them found less low calcium after surgery (Khatiwada 2021). Take it only as your surgical team directs.

What we'd skip

  • Bugleweed (Lycopus). Its main study was open (everyone knew what they were taking) in people with mild overactive-thyroid symptoms, not a blinded trial with a dummy pill (Beer 2008).
  • Chinese herbal mixtures. A Cochrane review found 13 trials (1,770 people), all of low quality, and could not recommend any preparation (Zen 2007).

Safety and interactions

  • Antithyroid medicine: high-dose iodine adds to its effect and can make thyroid levels fall too low (NIH ODS). No studies have tested selenium, carnitine or vitamin D for interactions with methimazole, but in the trials above they were taken alongside it.
  • Radioactive iodine or surgery: tell the team every supplement you take, especially kelp, iodine and biotin, before you start.
  • Thyroid blood tests: biotin can distort them (Elston 2016). Mention it every time.
  • Selenium: count every source, including multivitamins and Brazil nuts, and check your stack against the upper limits.
  • Smoking makes Graves' eye disease worse, even after the thyroid is treated (MedlinePlus), and the European guideline lists it first among the risk factors to control (EUGOGO 2021).
  • Pregnancy: Graves' medicines change in pregnancy (the methimazole label warns of birth defects with first-trimester use, and propylthiouracil carries a liver-failure warning), so every medicine and supplement, including the iodine in prenatal vitamins, should be as advised by your endocrinologist and your midwife or obstetric team (DailyMed methimazole; DailyMed propylthiouracil).
  • Breastfeeding? Ask your midwife, doctor or a lactation specialist, who can check what passes into breast milk.
  • Under 18? A clinician should advise you.

When to see a doctor

  • Call 911 or your local emergency number if you have an overactive thyroid with fever, confusion or drowsiness, a racing or irregular heartbeat, or sudden shortness of breath: these can be signs of thyroid storm, an emergency (MedlinePlus Graves disease; MedlinePlus thyroid storm).
  • On methimazole, carbimazole or propylthiouracil: fever or a sore throat needs an urgent call to your doctor, because these medicines can rarely wipe out infection-fighting white blood cells (agranulocytosis) (DailyMed methimazole; Burch 2015).
  • Yellowing skin or eyes, itching, dark urine, pale stools or pain in the upper right belly on propylthiouracil can mean liver injury: its label says to stop it and call your doctor right away (DailyMed propylthiouracil).
  • Eye problems that get worse, such as new double vision, blurred sight or more painful, bulging eyes: contact your doctor promptly (MedlinePlus).
  • Symptoms that come back after treatment, such as a fast heartbeat, weight loss or shaking: ask for a thyroid test.

Never stop or change a prescribed medicine by yourself; check with your endocrinologist or pharmacist first.

FAQ

What supplements should I avoid with Graves' disease? Kelp and other iodine supplements, "thyroid support" pills (most tested held real thyroid hormone) and ashwagandha, which has been linked to thyrotoxicosis in case reports. Tell your doctor about biotin before blood tests, because it can make results look like Graves' disease.

Does selenium help Graves' disease? For mild Graves' eye disease, selenium improved eye-related quality of life in a trial of 159 people, and the European guideline lists it where people are short of selenium (grade B); later trials agree less, and pooled trials showed no clear quality-of-life gain. For the overactive thyroid itself, it did not change remission in a trial of 430 people (grade B).

Can I take ashwagandha with hyperthyroidism? It is best avoided. Case reports link it to thyrotoxicosis (grade D), and NCCIH says it is not recommended for people with thyroid disorders.

Is kelp good for an overactive thyroid? No. Kelp is rich in iodine, and kelp tea and diet products have set off hyperthyroidism in case reports (grade C). Iodine on top of antithyroid medicine can also push thyroid levels too low.

Can I take shilajit with hyperthyroidism? No studies have tested it in people with an overactive thyroid. Check the label for kelp, iodine or ashwagandha, and ask your endocrinologist.

Sources

  1. Burch HB, et al. Management of Graves Disease: A Review. JAMA. 2015. PubMed 26670972 · doi:10.1001/jama.2015.16535
  2. Kang GY, et al. Thyroxine and triiodothyronine content in commercially available thyroid health supplements. Thyroid. 2013. PubMed 23758055 · doi:10.1089/thy.2013.0101
  3. Müssig K, et al. Iodine-induced thyrotoxicosis after ingestion of kelp-containing tea. J Gen Intern Med. 2006. PubMed 16808731 · doi:10.1111/j.1525-1497.2006.00416.x
  4. van der Hooft CS, et al. [Thyrotoxicosis following the use of ashwagandha]. Ned Tijdschr Geneeskd. 2005. PubMed 16355578
  5. Elston MS, et al. Factitious Graves' Disease Due to Biotin Immunoassay Interference-A Case and Review of the Literature. J Clin Endocrinol Metab. 2016. PubMed 27362288 · doi:10.1210/jc.2016-1971
  6. Marcocci C, et al. Selenium and the course of mild Graves' orbitopathy. N Engl J Med. 2011. PubMed 21591944 · doi:10.1056/NEJMoa1012985
  7. Kostadinov N, et al. Efficacy of Selenium Supplementation in Graves' Orbitopathy: A Systematic Review and Meta-Analysis of Randomized Controlled Trials with Trial Sequential Analysis. J Clin Med. 2026. PubMed 42355878 · doi:10.3390/jcm15124710
  8. Zheng H, et al. Effects of Selenium Supplementation on Graves' Disease: A Systematic Review and Meta-Analysis. Evid Based Complement Alternat Med. 2018. PubMed 30356415 · doi:10.1155/2018/3763565
  9. Cramon PK, et al. Selenium supplementation in individuals with newly diagnosed Graves' hyperthyroidism: a double-blind, multi-centre RCT. Eur Thyroid J. 2026. PubMed 41384622 · doi:10.1530/ETJ-25-0264
  10. Grove-Laugesen D, et al. Effect of Vitamin D Supplementation on Graves' Disease: The DAGMAR Trial. Thyroid. 2023. PubMed 37218433 · doi:10.1089/thy.2023.0111
  11. Grove-Laugesen D, et al. Effects of Supplemental Vitamin D on Muscle Performance and Quality of Life in Graves' Disease: A Randomized Clinical Trial. Thyroid. 2020. PubMed 31910101 · doi:10.1089/thy.2019.0634
  12. Sohn SY, et al. Risks of Iodine Excess. Endocr Rev. 2024. PubMed 38870258 · doi:10.1210/endrev/bnae019
  13. Di Matola T, et al. Thyroid dysfunction following a kelp-containing marketed diet. BMJ Case Rep. 2014. PubMed 25355748 · doi:10.1136/bcr-2014-206330
  14. Kamal HI, et al. Ashwagandha as a Unique Cause of Thyrotoxicosis Presenting With Supraventricular Tachycardia. Cureus. 2022. PubMed 35475098 · doi:10.7759/cureus.23494
  15. Hayashi M, et al. Painless Thyroiditis by Withania somnifera (Ashwagandha). Cureus. 2024. PubMed 38559552 · doi:10.7759/cureus.55352
  16. Bartalena L, et al. The 2021 European Group on Graves' orbitopathy (EUGOGO) clinical practice guidelines for the medical management of Graves' orbitopathy. Eur J Endocrinol. 2021. PubMed 34297684 · doi:10.1530/EJE-21-0479
  17. Ahn HY, et al. Selenium vs Control for Graves Ophthalmopathy in a Selenium-Sufficient Area: A Randomized Clinical Trial. JAMA Ophthalmol. 2025. PubMed 40014353 · doi:10.1001/jamaophthalmol.2024.6337
  18. Vinceti M, et al. Selenium for preventing cancer. Cochrane Database Syst Rev. 2018. PubMed 29376219 · doi:10.1002/14651858.CD005195.pub4
  19. Kahaly GJ, et al. Double-Blind, Placebo-Controlled, Randomized Trial of Selenium in Graves Hyperthyroidism. J Clin Endocrinol Metab. 2017. PubMed 29092078 · doi:10.1210/jc.2017-01736
  20. Benvenga S, et al. Usefulness of L-carnitine, a naturally occurring peripheral antagonist of thyroid hormone action, in iatrogenic hyperthyroidism: a randomized, double-blind, placebo-controlled clinical trial. J Clin Endocrinol Metab. 2001. PubMed 11502782 · doi:10.1210/jcem.86.8.7747
  21. Rossi M, et al. Adding L-Carnitine and Selenium to Methimazole in Graves' Disease: A Prospective Randomized Trial on Thyroid Markers and Quality of Life. Nutrients. 2025. PubMed 40871722 · doi:10.3390/nu17162693
  22. Grove-Laugesen D, et al. Changes in bone density and microarchitecture following treatment of Graves' disease and the effects of vitamin D supplementation. A randomized clinical trial. Osteoporos Int. 2024. PubMed 39264438 · doi:10.1007/s00198-024-07241-y
  23. Oltmann SC, et al. Preventing postoperative hypocalcemia in patients with Graves disease: a prospective study. Ann Surg Oncol. 2015. PubMed 25212835 · doi:10.1245/s10434-014-4077-8
  24. Khatiwada AS, et al. Use of pre-operative calcium and vitamin D supplementation to prevent post-operative hypocalcaemia in patients undergoing thyroidectomy: a systematic review. J Laryngol Otol. 2021. PubMed 34120662 · doi:10.1017/S0022215121001523
  25. Beer AM, et al. Lycopus europaeus (Gypsywort): effects on the thyroidal parameters and symptoms associated with thyroid function. Phytomedicine. 2008. PubMed 18083505 · doi:10.1016/j.phymed.2007.11.001
  26. Zen XX, et al. Chinese herbal medicines for hyperthyroidism. Cochrane Database Syst Rev. 2007. PubMed 17443591 · doi:10.1002/14651858.CD005450.pub2