Why Do I Have Thyroid Symptoms If My TSH Is Normal?

Some people treated for hypothyroidism may still experience symptoms even if blood tests show that their thyroid stimulating hormone (TSH) levels are well within the normal range. The reasons for this are complex, but the bottom line is that having a normal TSH value doesn't necessarily mean that all of your symptoms will go away.

In fact, your TSH blood tests may say that you are clinically euthyroid (normal), but you may still experience many of the same problems you had prior to treatment, including:

  • Chronic fatigue
  • Weight gain despite no change in diet
  • Feeling cold all the time
  • Muscle and joint aches
  • Itchy and dry skin
  • Hair loss
  • Depression
  • Difficulty concentrating
  • Chronic constipation
  • Heavy or irregular periods

Causes

Evidence suggests that situations like this are not as uncommon as one may think. Even when placed on levothyroxine—the drug considered the gold standard of hypothyroid treatment—many people fail to reap the physical benefits of treatment.

A 2016 study from Rush University reported that people on levothyroxine alone were an average of 10 pounds heavier than people without thyroid disease, despite eating less, and were more likely to be on antidepressants, beta blockers, and statin drugs.

What this tells us is that having "healthy" blood results doesn't necessarily mean you will feel healthy. This is because the normalization of TSH levels only paints a part of the picture of what "normal" thyroid function is all about.

Mechanisms of Thyroid Function

Many people assume that TSH is a thyroid hormone, but it's actually not. It is a hormone produced by the pituitary gland, the organ that detects whether thyroid hormone levels in the blood are high or low. If the latter, the pituitary gland will secrete TSH to spur the thyroid gland into action.

The thyroid gland will produce several different hormones. The role of these hormones is to regulate body metabolism (the conversion of oxygen and calories into energy). The main hormone is thyroxine (T4), which only has a moderate effect on metabolism.

However, when thyroxine loses a molecule of iodine in a process called monodeiodination, it is converted into triiodothyronine (T3), the "active" thyroid hormone able to exert four times the hormonal strength of T4.

Possible Explanations

While the mechanisms of thyroid function may seem clear and simple, they can vary from one person to the next. And, oftentimes, the tests used to monitor thyroid function provide only a glimpse of a person's true clinical picture.

Levothyroxine therapy is typically monitored with TSH and T4 blood tests. The presumption is that if T4 levels are restored to the normal range, T4 will naturally convert to T3 and deliver more of the active hormone the body needs. Experts are finding that is not always the case.

The Rush University study found that people on levothyroxine alone tended to have a lower ratio of T3 to T4 hormones compared to the general population, meaning that T3 may be deficient despite achieving the diagnostic goals for hypothyroidism.

While the reasons for this could be many, including a genetic resistance to levothyroxine or chromosomal defects like deiodinase polymorphism (which impede T3 conversion), the bottom line is that levothyroxine "success" can often be measured in labs but not be felt in real life.

What to Do If Symptoms Persist

In the past, people who felt unwell despite normal TSH and T4 levels were faced with a certain skepticism by doctors and others. In some cases, they would be referred for psychological counseling or assumed to be cheating on a diet if their weight continued to increase.

While doctors today better understand the variability of thyroid hormone replacement therapy, you may still need to advocate for yourself if there is any suggestion that your symptoms are "in your head."

Ask Your Doctor if a New TSH Target Is Appropriate

When assessing your response to treatment, many doctors will aim to get your TSH level to around 1 to 2 mU/L—the lower end of the normal range.

While you may be told that TSH levels of 1 to 2 mU/L are "fine" if you have mild hypothyroidism, it is possible to still have symptoms, especially if your levels tend to fluctuate.

To this end, some endocrinologists have lowered the TSH threshold from the standard normal range of 0.5 to 5 mU/L to a revised normal range of 0.3 to 3.0 mU/L. By tightening your hormonal controls to the lower end of the revised range, you may be less prone to symptoms.

Consider Other Levothyroxine Brands

Levothyroxine is the generic name of the drug marketed under many different brand names. The majority of people first starting treatment will be prescribed the Synthroid brand. Other available brands include Levoxyl, Levothroid, and Unithroid.

While the U.S. Food and Drug Administration (FDA) tightly regulates the type, purity, and amount of key active and inactive ingredients in a drug, different manufacturers (particularly generics manufacturers) may use different fillers and binding ingredients, some of which may affect drug absorption or trigger adverse symptoms. Changing brands may potentially alleviate unintended side effects. Talk to your doctor about whether this might be right for you.

Avoid Generics or Get a Stable, Multiple-Month Batch

Some HMOs and insurance companies will automatically override your doctor's requested brand and supply you with a generic levothyroxine made by one of many different manufacturers.

There is nothing inherently wrong with generic drugs. The problem with this practice, however, is that you may be switched from one generic brand to the next every month without even knowing it. And, each time you are, you may receive a product that has a slightly different potency or is closer to the expiration date that you might otherwise prefer.

To ensure medication consistency, ask your doctor to write "no generic substitution" or "DAW" (dispense as written) on the prescription. If your insurer threatens a higher drug copay, ask your doctor to write a motivation outlining why the specific brand is necessary.

If your insurer denies your request, ask your doctor to write a prescription for a six-month drug supply, which most companies will agree to. Once received, check to ensure the drugs are all from the same manufacturer and are within the expiration date for at least the next six months.

Inquire About a T3 Drug

There are many doctors who consider the addition of a T3 hormone, in the form of Cytomel (liothyronine), wholly unnecessary and problematic. They will point to the fact that it is prone to rapid uptake in the intestines and may quickly turn a hypothyroid problem into a hyperthyroid problem. T3 hormones can also interfere with T4 blood test results and complicate the monitoring of your disease. All of these things are true, but to a degree.

If you are able to maintain control of your TSH and T4 but are feeling unwell, the addition of Cytomel may improve your symptoms, according to research from Spain and the National Institute of Diabetes and Digestive and Kidney Diseases.

The same research suggests that the combination of Cytomel and levothyroxine may improve symptoms without any additional side effects compared to levothyroxine alone.

Ask Your Doctor About Natural Desiccated Thyroid (NDT)

In recent years, an increasing number of people are embracing a century-old treatment called natural desiccated thyroid (NDT), which is derived from the dried thyroid gland of pigs or cows. NDT delivers T4, T3, and other thyroid hormones in a tablet form and is today used by the likes of Hillary Rodham Clinton and others to manage their hypothyroid symptoms.

While NDT is not officially approved for the treatment of hypothyroidism, it is regulated by the FDA and allowed to be sold by prescription, having been "grandfathered" in as a standard of care since the 1950s.

NDT is marketed under many different brand names, including Armour Thyroid, Nature-Throid, WP Thyroid, and others.

A Word From Verywell

Treatment guidelines issued by the American Association of Clinical Endocrinologists (AACE) and American Thyroid Association (ATA) provide doctors a valuable roadmap for the treatment of hypothyroidism. Despite this, there remains significant contention among clinicians about facets of the guidelines, including how to treat subclinical (non-symptomatic) hypothyroidism and the appropriate use of Cytomel.

To this end, you need to take steps to find an experienced endocrinologist who is able to work with you as a partner in your care. You should be able to freely discuss complementary and alternative options without constraint and work together to weigh the pros and cons of treatment so that you can make a fully informed choice.

If you are uncertain about the care you are receiving, do not hesitate to seek a second opinion or to ask that your medical records be forwarded to another doctor.

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