Last Chance - Mother's Day Sale

Last chance - Mother's Day Sale

For moms, thyroid health matters. Save $25 on our thyroid test kit or self-pay membership using code MOMDAY.

Going From Hypothyroid to Hyperthyroid – and Back Again!

What causes fluctuations between hypothyroidism and hyperthyroidism?
Going From Hypothyroid to Hyperthyroid – and Back Again!
Last updated:
Written by:
Medically Reviewed by:

In this article:

In a perfect world, when you’re hypothyroid, you’ve found a great healthcare provider, and you’re taking the right thyroid hormone replacement medication for you. You’ve optimized your thyroid levels, and, voila…life is good! You get retested every 3 to 6 months; ideally, your levels don’t change, so you stay on the same medication dosage. And you keep on feeling well!

Hold on! For some people with hypothyroidism, things aren’t quite this steady. You may go through periods when your thyroid fluctuates from hypothyroidism to hyperthyroidism and back to hypothyroidism – sometimes multiple times a year.

In this article, we explore some common reasons you may go from hypothyroidism to hyperthyroidism – and back again!


One of the most common causes of shifts from hypothyroidism to hyperthyroidism is taking too much thyroid hormone replacement medication. Several situations can cause overmedication: 

  1. Weight Loss: You’ve lost weight but stayed on the same dose of thyroid medication. (Weight loss frequently requires a reduction in your dosage.)
  2. Pharmacy Error: Pharmacies fill your prescription incorrectly with higher-dosage medication.
  3. Generic Refills: Different manufacturers’ potency of generic levothyroxine can fluctuate from 95 to 105% of the stated potency. That means if you’re stabilized on a prescription from one generic manufacturer and get a refill from your pharmacy, they can fill it with any generic levothyroxine. If you go from a lower potency to a higher potency, this can result in hyperthyroidism.


In the U.S., most hypothyroidism is caused by Hashimoto’s, an autoimmune disease. One unique characteristic of autoimmune diseases is the tendency to go through cycles of flare-ups – when autoimmune thyroid disease becomes more acute, and TSH levels can rise – followed by remission periods when hypothyroidism calms down and TSH levels drop. If you get your hypothyroidism optimized during a flare, remission could change your thyroid levels enough to cause a period of hyperthyroidism.


Thyroiditis – an inflammatory condition affecting your thyroid gland – can be triggered by a viral or bacterial infection or an autoimmune disease like Hashimoto’s Thyroiditis.

When you have thyroiditis, the hormonal output of your gland is frequently unstable. At times, your gland may produce more thyroid hormone, leading to periods of hyperthyroidism, followed by a return to thyroid levels in the reference range or back to hypothyroidism again. Apart from Hashimoto’s, thyroid function usually returns to normal after recovery from most forms of thyroiditis.

After childbirth, thyroiditis – with shifts between hypothyroidism and hyperthyroidism – is more common. This postpartum thyroiditis can occur up to 12 months after delivery, and frequently begins with an overactive thyroid, eventually shifting into hypothyroidism in most women. This hyperthyroid phase of postpartum thyroiditis can affect women who are already being treated for hypothyroidism.


The change of seasons can affect your thyroid function to the extent that it can shift you from normal levels into hypothyroidism or hyperthyroidism. Researchers have found that circulating TSH levels are frequently higher during the winter cold, and this effect is even more pronounced in women. The TSH levels then tend to decrease in spring and summer. Overall, the levels can vary from 10 to 15% between seasons. This means that if you’re well-regulated during the winter, you may shift into hyperthyroidism during spring or summer. (There are even anecdotal reports of thyroid patients taking a winter vacation in a sunny, tropical location who become temporarily hyperthyroid as a result!)


Your diet can affect your thyroid levels. For example, if you start overconsuming raw goitrogenic vegetables (like spinach, broccoli, and cabbage), this can slow your thyroid down. Similarly, if you cut those foods out of your diet, your thyroid function might improve, even to the extent that you could shift from normal thyroid levels to hyperthyroidism.

Dietary fiber is also a factor that can affect your thyroid levels while on thyroid hormone replacement medication. Going quickly from low-fiber to high-fiber intake can interfere with the absorption of your thyroid medication and worsen your hypothyroidism. Conversely, going from a high- to a low-fiber diet could shift you into hyperthyroidism.

When taken too closely to your medication, milk, coffee, and calcium- and iron-rich foods can all interfere with the absorption of thyroid drugs. For example, if you take your morning thyroid medication right before you drink coffee, you’ll likely need a higher dose to overcome the absorption problems caused by the coffee. If you started drinking your coffee an hour after taking your thyroid medication, you could better absorb the medication, which could make you slightly hyperthyroid. (Read “How and When to Take Your Thyroid Medication” for advice on the best way to ensure optimal absorption.)

Finally, changes in your dietary iodine intake – for example, from iodine-rich foods like seaweed salad or sushi – can affect your thyroid and trigger overactive or underactive thyroid function.


Thyroid function can fluctuate in people treated for cancer with chemotherapy drugs. Research has shown that hypothyroidism—sometimes preceded by a short phase of hyperthyroidism—develops in around 40% of patients taking tyrosine kinase inhibitor (TKI) cancer drugs. You may recognize the names of some of the more common TKI drugs, like erlotinib (Tarceva) and imatinib (Gleevec).

In one study, about 53% of women developed subclinical or overt hypothyroidism after treatment with TKI drugs, compared to 34% of men.

Medications and Supplements

A number of medications can interfere with your thyroid hormone levels and trigger shifts to hypothyroidism or hyperthyroidism. These include:

  • Metformin, the most commonly prescribed drug used to treat type 2 diabetes
  • Amiodarone, a drug for heart arrhythmias
  • Lithium, used to treat bipolar disorder
  • Steroid (glucocorticoid) drugs, like prednisone
  • Iodine supplements, including potassium iodide, Lugol’s Solution, kelp, and bladderwrack
  • Supplements that contain soy, calcium, iron, or biotin
  • Over-the-counter thyroid glandular supplements, which can contain undisclosed amounts of actual thyroid hormone

Estrogen – found in birth control pills and hormone replacement therapy (HRT) – has a well-known effect on the thyroid. This hormone increases the need for thyroid hormone in women with hypothyroidism. This means that if a woman takes both thyroid hormone replacement and estrogen and stops taking the estrogen drug, she could become hyperthyroid on her current dose of thyroid medication.

Experts recommend that women on thyroid hormone replacement therapy for hypothyroidism have a complete thyroid panel done 12 weeks after starting or stopping an estrogen drug.

A note from Paloma

If you are being treated for hypothyroidism and notice that you’ve developed symptoms of hyperthyroidism or symptoms of hypothyroidism, an essential first step is to quickly evaluate your thyroid hormone levels. The process can be inconvenient, expensive, and even painful, especially when you need a doctor’s appointment for a blood draw or a time-consuming trip to the testing lab. Paloma Health’s Complete Thyroid Home Test kit makes the process simple and affordable. Your Paloma test kit lets you conveniently test at home with painless and accurate fingerstick testing. The test panel includes Thyroid Stimulating Hormone (TSH), Free Thyroxine (Free T4), Free Triiodothyronine (Free T3), and Thyroid Peroxidase Antibodies (TPOAb). You also have the option at checkout to add Reverse T3 (RT3) and Vitamin D tests to your panel. Testing is easy: just order your kit online, follow the simple instructions to take your samples, and send your test kit back in the prepaid mailer to our certified lab, where your tests will be quickly processed.  Your results will quickly be available in your secure online portal!


Thomson RJ, Moshirfar M, Ronquillo Y. Tyrosine Kinase Inhibitors. PubMed. Published 2021.

‌Razvi S, Bhana S, Mrabeti S. Challenges in Interpreting Thyroid Stimulating Hormone Results in the Diagnosis of Thyroid Dysfunction. Journal of Thyroid Research. Published September 22, 2019.

McMillan, K. S. Rotenberg, K. Vora et al., “Comorbidities, concomitant medications, and diet as factors affecting levothyroxine therapy: results of the CONTROL surveillance project,” Drugs in R&D, vol. 16, no. 1, pp. 53–68, 2016.

D. Faix and L. M. Thienpoint, Thyroid-Stimulating Hormone. Why Efforts to Harmonize Testing are Critical to Patient Care, American Association of Clinical Chemists, Washington, DC, USA, 2013,

Koulouri O, Moran C, Halsall D, Chatterjee K, Gurnell M. Pitfalls in the measurement and interpretation of thyroid function tests. Best Pract Res Clin Endocrinol Metab. 2013;27(6):745-62. doi:10.1016/j.beem.2013.10.003

Arafah B.M. Increased Need for Thyroxine in Women with Hypothyroidism during Estrogen Therapy. New England Journal of Medicine. 2001;344(23):1743-1749. doi:10.1056/nejm200106073442302

‌Kuzmenko NV, Tsyrlin VA, Pliss MG, Galagudza MM. Seasonal variations in levels of human thyroid-stimulating hormone and thyroid hormones: a meta-analysis. Chronobiology International. 2021;38(3):301-317. doi:10.1080/07420528.2020.1865394

De Grande LA, Goossens K, Van Uytfanghe K, Halsall I, Yoshimura Noh J, Hens K, et al. Using “Big Data” to Describe the Effect of Seasonal Variation in Thyroid-Stimulating Hormone. Clin Chem Lab Med (2017) 55(2):e34–6. doi: 10.1515/cclm-2016-0500

Fariduddin MM, Singh G. Thyroiditis. PubMed. Published 2021.

Share article:

Mary Shomon

Patient Advocate

Mary Shomon is an internationally-recognized writer, award-winning patient advocate, health coach, and activist, and the New York Times bestselling author of 15 books on health and wellness, including the Thyroid Diet Revolution and Living Well With Hypothyroidism. On social media, Mary empowers and informs a community of more than a quarter million patients who have thyroid and hormonal health challenges.

Read more

Is Paloma Right For Me?

Hypothyroidism is a long-term commitment and we’re committed to you. Schedule a free, no-obligation phone consultation with one of our intake specialists to find out more.

Schedule a call
thyroid hormone for hypothyroidism

Find out if Paloma is right for you. Schedule a free call with one of our health care advisors.

Schedule a Call