Why Your Thyroid Hormone Levels May Be Fluctuating

If you have thyroid disease, you may experience some fluctuations in your thyroid hormone levels from time to time. These fluctuations can occur as your thyroid disease progresses.

But other factors, such as hormonal changes and medication variations, or significant weight gain or loss, can alter your thyroid hormone levels as well; in some cases progression of a thyroid condition (such as a nodule) may be responsible. These hormonal fluctuations can produce a variety of symptoms.

This article explains what things might contribute to thyroid hormone fluctuations and what you can do about it.

why thyroid levels fluctuate

Verywell / Brianna Gilmartin

Thyroid Disease Progression

Thyroid disease can remain stable or worsen as the years go on. These changes may occur for a couple of reasons:


How the Thyroid Gland Works

Hashimoto's Thyroiditis

Hashimoto's thyroiditis often progresses over the first 10 years. After you receive a diagnosis and treatment plan, thyroid antibodies may continue to attack the thyroid gland. These attacks make your thyroid less able to produce thyroid hormone on its own.

Therefore, if you maintain the same treatment dose, your thyroxine (T4) and triiodothyronine (T3) thyroid hormone levels can drop. These hormonal drops cause your thyroid-stimulating hormone (TSH) to rise in response.

Overall, you might feel the symptoms of hypothyroidism, which include:

  • Fatigue
  • Weight gain
  • Depression

Graves' Disease

Graves' disease can also progress, especially in the first few years after diagnosis. In many instances, even when your treatment is at the correct dose, you may notice the following effects of disease progression:

  • Rise in T3 and T4 levels
  • Falling TSH levels
  • Symptoms of hyperthyroidism, such as the inability to concentrate, insomnia, and weight loss

With Graves' disease, the opposite can happen, too. In some cases, after months or years of taking antithyroid medications, your condition can go into remission. However, when that happens, your T3 and T4 levels may decrease (while your TSH rises). In this situation, you can also develop symptoms of hypothyroidism.

Thyroiditis After Pregnancy

Some people develop thyroiditis after pregnancy. Usually, this is characterized by low thyroid hormone levels and high or low TSH. But high thyroid hormone levels with low or high TSH can develop as well.

Usually, postpartum thyroiditis will resolve itself. Often, over time, the thyroid hormones and TSH eventually return to normal.

However, during the period of thyroiditis, your doctor may prescribe thyroid hormone replacement or antithyroid medications. Often, people can decrease or discontinue these medications if and when the condition improves.


Pregnancy can affect thyroid hormones in many ways. However, the changes in these levels are more extreme if you already have a thyroid condition before becoming pregnant.

  • Without pre-pregnancy thyroid disease: T3 and T4 tend to increase while TSH decreases during pregnancy. These fluctuations happen because human chorionic gonadotropin (HCG), a hormone produced during pregnancy, stimulates the production of T3 and T4.
  • Hyperthyroid before pregnancy: In this case, the effect of HCG can increase your T4 and T3 and decrease your TSH even more than usual during your pregnancy.
  • Hypothyroid before pregnancy: The demand for thyroid hormone for fetal development increases in pregnancy. This increased demand may result in the need for your doctor to adjust the dose of medication.


Disease progression can impact thyroid hormone levels. How your hormones respond over time depends on which type of thyroid disease you have.

Medication Potency Differences

Sometimes when you are taking thyroid medication, your thyroid hormone blood levels may change. For example, this might happen if you've gotten a refill of your thyroid hormone replacement medication or used a different pharmacy.

Within the Food and Drug Administration (FDA) guidelines, thyroid hormone replacement medications can vary in their potency.

The federal guidelines say that levothyroxine drugs must be within 95% to 105% of the stated potency. That means a 100-mcg pill can be considered potent even though it delivers anywhere from 95 mcg to 105 mcg of the active ingredient.

Brands and Manufacturers

Potency tends to be reasonably stable within a particular brand name or generic manufacturer. However, medications can vary from one manufacturer to another. So, if you tend to switch brands or manufacturers, you might notice some swings in your levels.

Depending on your condition, these potency variations can cause mild increases or decreases in your T4, T3, or TSH. They can also contribute to related symptoms of hypothyroidism or hyperthyroidism.

Medication Errors

Also, keep in mind that prescription errors can occur. So one crucial tip is always to double-check your medication. Look at the label and the actual pills, and make sure you're getting the drug and the dosage your doctor prescribed.


Potencies can vary from different brands and manufacturers. If you are on generic medication, work with your pharmacist to ensure that you always get medicines from the same generic manufacturer. Alternately, you could consider switching to a brand name to avoid this issue.

Thyroid Disease Doctor Discussion Guide

Get our printable guide for your next doctor's appointment to help you ask the right questions.

Doctor Discussion Guide Old Woman

When and How You Take Your Pill

Taking your medication at the same time every day is essential. Not only does it help you establish a habit and make it less likely for you to miss a dose, but it also ensures that you always take it in the same way. In addition, there are some other things to keep in mind when taking thyroid medication.

Take It On An Empty Stomach

You should take thyroid replacement or antithyroid medication on an empty stomach. That's because food may delay or reduce the drug's absorption by changing the rate at which it dissolves or by changing acid levels in the stomach. Ultimately, this can affect your thyroid hormone levels, your symptoms, and your test results.

Take It Consistently

If you want to ensure the best possible absorption of your medication, take your thyroid medication consistently. Ideally, you should take your thyroid medicine in the morning, on an empty stomach, about one hour before eating breakfast and drinking coffee. Alternately, you could take it at bedtime (at least three hours after your last meal).

Spread Out Other Supplements

Make sure to wait for at least three to four hours between taking thyroid medication and any fiber, calcium, biotin, or iron supplements. These nutrients can prevent you from absorbing your full dose of medication.

Ultimately, when it comes to taking your thyroid hormone drug, consistency is essential. If you plan to change how you take your thyroid medication, make sure you clear it with your healthcare provider first. 

Other Medications and Herbs

Some herbal supplements and medications can have an impact on thyroid hormone levels. They may affect your hormones by:

  • Competing with the body's thyroid hormone activity
  • Increasing the effects of thyroid hormones
  • Altering medication absorption and activity


Starting or stopping prescription drugs that you take for other conditions can affect your thyroid levels and symptoms. Some medications that may affect thyroid levels include:

  • Certain cholesterol-lowering drugs
  • Corticosteroids
  • Growth hormone
  • Lithium
  • Amiodarone
  • Beta blockers


Certain herbs are known to increase or decrease thyroid function, alter test results, and produce various thyroid-related symptoms. These herbs include:

  • The Ayurvedic herb guggul
  • Supplements such as tyrosine and bladderwrack
  • Products like kelp that contain iodine

It is best to ask your pharmacist and healthcare provider about potential interactions with any herbs or supplements you plan to take.

Change of Seasons

Thyroid levels and TSH, in particular, can change along with the seasons. For example, TSH naturally rises somewhat during colder months and drops back down in the warmest months.

Some healthcare providers adjust for this. For example, they may prescribe slightly increased thyroid replacement dosages during colder months and reduced dosages during warm periods. 


For people with thyroid disease, certain things can cause fluctuations in thyroid hormone levels. These may include disease progression, medication changes, other herbs and supplements, and the change of seasons.

Things that may help keep your thyroid levels stable include taking your thyroid medication at the same time every day and on an empty stomach; sticking with the same brand or manufacturer of your thyroid medication; talking to your doctor about other medicines, herbs, and supplements you currently take; and asking your doctor about adjusting your medication dose with the change of seasons.

A Word From Verywell

Careful management of your thyroid levels is an essential part of your thyroid treatment. Several factors can alter your symptoms and thyroid test results. Addressing these issues can help keep your thyroid levels stable.

If you notice a change in your symptoms, be sure to tell your healthcare provider, who might want you to have your thyroid hormone levels retested. Depending on the results, they may adjust your medication dosing.

8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Jonklaas J, Bianco AC, Bauer AJ, et al. Guidelines for the treatment of hypothyroidism: prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement. Thyroid. 2014;24(12):1670-751. doi:10.1089/thy.2014.0028

  2. U.S. Department of Health and Human Services, Office on Women's Health. Hashimoto's disease.

  3. Wong M, Inder WJ. Alternating hyperthyroidism and hypothyroidism in Graves' disease. Clin Case Rep. 2018;6(9):1684-1688. doi:10.1002/ccr3.1700

  4. Cleveland Clinic. Thyroiditis.

  5. Cleveland Clinic. Postpartum thyroiditis: management and treatment.

  6. U.S. Department of Health and Human Services, National Institute of Diabetes and Digestive and Kidney Diseases. Thyroid disease and pregnancy.

  7. Harvard Health Publishing. Drugs that interact with thyroid medication.

  8. Wang D, Cheng X, Yu S, et al. Data mining: seasonal and temperature fluctuations in thyroid-stimulating hormone. Clin Biochem. 2018;60:59-63. doi:10.1016/j.clinbiochem.2018.08.008

Additional Reading

By Mary Shomon
Mary Shomon is a writer and hormonal health and thyroid advocate. She is the author of "The Thyroid Diet Revolution."