Why Your Thyroid Hormone Levels May Be Fluctuating

8 Reasons You May Not Be Aware Of

Updated on October 30, 2023

Medically reviewed by Danielle Weiss, MD

If you have thyroid disease, your thyroid-stimulating hormone (TSH) levels can fluctuate from time to time. These fluctuations can occur as your thyroid disease progresses or from other factors such as your age, changes in weight, pregnancy, drug interactions, and even seasons.

This article describes eight different factors that can cause thyroid hormone fluctuations and what you can do about them.

why thyroid levels fluctuate — Verywell / Brianna Gilmartin

Thyroid Disease Progression

Fluctuations in TSH levels can occur as your thyroid disease progresses. The rate of progression is highly variable, with some people remaining stable for many years and others progressing relatively quickly. There may also be a pattern of worsening symptoms (exacerbations) followed by periods of low disease activity (remission).

This can occur in people with Hashimoto's disease, a form of hypothyroidism (underactive thyroid), and Grave's disease, a form of hyperthyroidism (overactive thyroid).

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How the Thyroid Gland Works

Hashimoto's Thyroiditis

Hashimoto's thyroiditis, the autoimmune form of hypothyroidism, tends to progress slowly over many years and often remains undiagnosed until the disease is advanced. Even when treatment is started, thyroid autoantibodies may continue to attack the thyroid gland.

In some cases, these attacks come in episodes known as flares. At other times, the assault may be persistent, progressively undermining the function of the thyroid gland.

If the latter happens and you maintain the same treatment dose, you might experience:

Falling thyroxine (T4) and triiodothyronine (T3) thyroid hormone levels
Rising TSH levels
Symptoms of hypothyroidism

Graves' Disease

Graves' disease (an autoimmune form of hyperthyroidism) can also progress, especially in the first few years following the diagnosis. Even with treatment, a low-level autoimmune assault on the thyroid gland may persist.

If the same treatment dose is maintained, the progressive damage to the gland can manifest with:

Rising T3 and T4 levels
Falling TSH levels
Symptoms of hyperthyroidism

The opposite can also happen. After years of taking antithyroid drugs, your condition can suddenly go into remission. When this happens, your T3 and T4 levels may drop while your TSH rises, leading to low thyroid symptoms.

Pregnancy

Pregnancy can affect thyroid hormones, whether you have thyroid disease or not. People who are pregnant often experience temporary thyroiditis (thyroid inflammation) that can cause T3 and T4 to increase and TSH levels to decrease.

Pregnancy can have the same effects on people with thyroid disease, albeit more extreme. Here is what commonly occurs in people with thyroid disease who become pregnant:

Hyperthyroidism: Increased T4 and T3 levels and decreased TSH levels
Hypothyroidism: Decreased T4 and T3 levels and increased TSH levels

The best way to deal with this is to ensure your thyroid hormones are regularly monitored during pregnancy. In this way, your medication doses can be adjusted to keep TSH levels within the optimal range.

Medication Potency

Sometimes when you are taking thyroid medications as directed, your hormone levels will change. This sometimes happens when you refill your thyroid medications and use a different pharmacy or receive a different generic.

Many people do not realize that within the U.S. Food and Drug Administration (FDA) guidelines, thyroid hormone replacement drugs can vary somewhat in their potency.

For example, with levothyroxine used in the treatment of hypothyroidism, the FDA allows the drug to be within 95% to 105% of the stated potency. What this means is that a 100-microgram (mcg) pill might actually deliver slightly higher or lower doses than advertised.

The best way to avoid this is to use the same pharmacy for all refills and to ensure the same brand of medication is dispensed with each visit.

Thyroid Disease Doctor Discussion Guide

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Dosing Problems

If you do not take your thyroid medications consistently or correctly, the therapeutic drug level—meaning the concentration of medication in your body needed for the drug to work—can quickly drop. Without a consistent therapeutic drug level, your thyroid hormone levels can fluctuate, sometimes precipitously.

There are three common mistakes people make when taking thyroid drugs:

Dosing with food: Thyroid medications need to be taken on an empty stomach. Food can delay or reduce drug absorption by changing the rate at which it dissolves or by exposing it to excess stomach acid during digestion.
Inconsistent dosing: This is one of the main reasons for TSH fluctuations. You need to take your medications consistently, typically in the morning on an empty stomach an hour before breakfast. Alternatively, you can take it at bedtime at least three hours after your last meal.
Dosing with supplements: Certain supplements can reduce drug absorption. To avoid this, you need to separate your thyroid medication dose from any fiber, calcium, biotin, tyrosine, or iron supplement you take by at least three to four hours.

Taking your thyroid medications at the same time every day is essential. By doing so, you can quickly establish a habit and ensure consistent therapeutic drug levels in your body.

Changes in Weight

Another factor that can influence therapeutic drug levels is weight. Simply put, the more weight you put on, the lower the overall concentration of the drug will be. Conversely, the more weight you lose, the higher the overall concentration will be.

This may be more of a long-term concern since people don't usually put on large amounts of weight all at once, but it can be an issue if you lose weight quickly (such as due to a rapid weight loss plan). In such cases, not only will your TSH levels fluctuate but so can estrogen levels which indirectly influence your thyroid hormones.

Drug Interactions

Some prescription drugs, over-the-counter medications, and herbal supplements can interact with your thyroid medications. In some cases, they can "compete" for the same enzymes used to break down your thyroid drug, causing levels of one drug to drop (reducing its effectiveness) and the other to rise (increasing the risk of side effects).

Drugs known to interact with thyroid medications include:

Aluminum-containing antacids
Beta-blockers
Cipro XR (ciprofloxacin)
Cholesterol-lowering drugs like cholestyramine
Corticosteroids (steroids)
Evista (raloxifene)
Human growth hormone (hGH)
Kelp supplements
Lithium
Pacerone (amiodarone)
Renvela (sevelamer)
Tyrosine
Xenical (orlistat)

To avoid interactions. advise your healthcare provider of any drugs you take or intend to take (including recreational drugs) if you are being treated for thyroid disease.

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 these seasonal variations. For example, they may prescribe slightly higher thyroid replacement doses during colder months and higher doses during warmer months.

Older Age

Older age affects the function of the thyroid gland whether you have thyroid disease or not. If you have thyroid disease, your healthcare provider may adjust your dose to compensate for expected changes in your TSH levels (as described below).

Age range	Normal TSH	High TSH
18-50 years	0.5–4.1 mU/L	Over 4.1 mU/L
51-70 years	0.5–4.5 mU/L	Over 4.5 mU/L
71 years and older	0.4–5.2 mU/L	Over 4.5 mU/L

If you are getting older and have a harder time keeping your TSH levels within the optimal range, ask your endocrinologist if a dose adjustment is feasible.

Summary

For people with thyroid disease, certain things can cause fluctuations in TSH levels. These include disease progression, medication changes, pregnancy, inadequate dosing, changes in weight, seasonal variations, and age.

If you notice a change in your symptoms, be sure to tell your healthcare provider who can have your thyroid hormone levels tested. Depending on the results, your medication dosage may be changed.

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