Understanding the 4 Main Thyroid Hormones and How They Affect Your Health

The thyroid is a small, butterfly-shaped gland at the base of your neck, it plays a starring role in regulating nearly every system in your body. Through the hormones it releases, the thyroid controls energy, metabolism, heart rate, body temperature, digestion, mood, and more.

In this article, we’ll dive into the four main thyroid hormones, explain what they do, share what happens when they go off balance, and give practical guidance on when and why to consult a specialist.

Read more Thyroid Problem: Symptoms, Testing & Treatment in Michigan

What Are the “4 Main” Thyroid Hormones?

When we speak about “thyroid hormones,” we mostly refer to four key players:

• Thyroxine (T4)
• Triiodothyronine (T3)
• Thyroid‑Stimulating Hormone (TSH)
• Calcitonin

Although not all of these directly influence metabolism in the same way, they all play essential roles in thyroid function and overall health.

T4 (Thyroxine)

T4 (Thyroxine) is the main hormone your thyroid gland produces. It’s called T4 because each molecule has four iodine atoms. T4 works like a “storage” hormone, it doesn’t do very much on its own. Instead, your body converts T4 into T3, the more active hormone that drives metabolism, energy, and many other functions.

Because T4 stays in your bloodstream longer (about a week), it acts like a steady reservoir. This gives your body a reliable supply it can turn into T3 whenever extra support or energy is needed.

T3 (Triiodothyronine)

T3 is the more active hormone. It contains three iodine atoms, which allows it to more powerfully influence cells throughout the body.

While some T3 is produced directly by the thyroid, most T3 (about 80–85%) arises when T4 is converted into T3 by enzymes (deiodinases) in tissues like the liver, kidneys, and brain. 

Because of this conversion, T3 is often called the “active” thyroid hormone.

TSH (Thyroid-Stimulating Hormone)

TSH is not produced by the thyroid itself, it’s made by the pituitary gland, a small gland at the base of your brain. But it plays a crucial regulatory role. TSH tells the thyroid how much T4 and T3 to produce, based on feedback from existing hormone levels. 

If T3 and T4 levels drop too low, TSH increases to stimulate more production. If T3 and T4 are too high, TSH decreases to slow production. This feedback loop, the so-called hypothalamic-pituitary-thyroid axis, keeps hormone levels balanced. 

Calcitonin

Calcitonin is another hormone produced by the thyroid, but unlike T3/T4, it doesn’t directly regulate metabolism. Instead, it helps manage calcium levels in the blood by lowering them when they get too high.

Because its effects differ significantly from T3/T4, calcitonin is often discussed separately. But for a full picture of thyroid output, it's worth noting.

Read more Top 3 Signs You Might Have a Thyroid Problem

How Thyroid Hormones Influence Your Body

Together, T3, T4, TSH, and calcitonin orchestrate a wide range of vital processes. Here’s how:

Metabolism & Energy

• T3 (and to a lesser extent T4) influences basal metabolic rate, that is, how quickly your body burns energy at rest.
  
  
• They affect how your body processes carbohydrates, fats, and proteins; how quickly it uses oxygen; and how efficiently it burns calories.
  
  
• That’s why a healthy thyroid supports stable energy levels, appropriate body weight, and efficient digestion.
  
  

Heart Rate, Temperature & Circulation

Thyroid hormones influence your heart rate, appetite, and even how warm (or cold) you feel.

Someone with a hyperactive thyroid (excess hormones) might feel hot, have a faster or irregular heartbeat, or experience shakiness and tremors. 

Growth, Development & Brain Function

Especially in children, sufficient thyroid hormone is crucial for proper growth, bone development, and brain maturation. 

In adults, proper thyroid balance helps maintain cognitive function, mood stability, and overall vitality.

Digestion, Skin, Hair, and More

Thyroid hormones also affect gut motility (how quickly your digestive system moves), absorption of nutrients, and tissue maintenance, including skin, hair, and nails. 

Calcitonin, meanwhile, helps regulate calcium, important for bone health and more. Because the influence of thyroid hormones is so widespread, even small imbalances can ripple through many aspects of health.

What Happens When Thyroid Hormone Levels Are Too High or Too Low

Because thyroid hormones impact so many bodily functions, imbalance can lead to a wide spectrum of symptoms, sometimes subtle, sometimes dramatic.

Too Much Thyroid Hormone: Overactive Thyroid / Hyperthyroidism / Thyrotoxicosis

When T3 and/or T4 levels are too high, your body goes into overdrive. Some common signs and symptoms:

• Rapid or irregular heartbeat, palpitations, or arrhythmia
• Unexplained weight loss despite normal or increased appetite
• Nervousness, irritability, trembling hands or muscle weakness, shaky hands
• Heat intolerance, excessive sweating, sensitivity to high temperature
• Increased bowel movements or loose stools
• Sleep disturbances, restlessness, difficulty sleeping
• Possible changes in menstrual cycle in women, fertility issues, eye changes or swelling of the neck (goiter)

Medical conditions associated with excess thyroid hormone include Hyperthyroidism (overactive thyroid), and sometimes Thyrotoxicosis, a broader term referring to high thyroid hormone activity in the body. 

According to standard blood tests, high “free” T4 or T3 combined with low TSH is commonly used to diagnose hyperthyroidism. 

Too Little Thyroid Hormone: Underactive Thyroid / Hypothyroidism

When T3 and T4 are too low, the body slows down, metabolism drops, energy diminishes, and many systems feel sluggish. Typical signs include:

• Fatigue, low energy, sluggishness
• Weight gain, even if eating habits haven’t changed
• Sensitivity to cold, feeling cold when others feel fine
• Slower heart rate, reduced appetite, constipation, digestive issues
• Mood disturbances: depression, brain fog, memory issues, slowed thinking
• Changes to hair, skin, nails; brittle nails, dry skin, hair thinning or loss

Often, low T3/T4 will lead to elevated TSH, because the pituitary tries to stimulate more thyroid production.

If untreated or if ignored, hypothyroidism can lead to complications including slowed growth (in children), poor bone health, cognitive decline, and systemic metabolic sluggishness.

Read more: Digestion & Thyroid Function: How Your Gut Affects Thyroid Health

Why Doctors Check TSH, T3 & T4: Understanding Thyroid Lab Tests

Diagnosing or evaluating thyroid health almost always involves lab tests. Here's why each marker matters:

• TSH: Often the first screen. Because of the feedback loop, changes in TSH frequently show up before noticeable changes in T3/T4.
• T4 (Total and Free): Measures how much thyroxine is in your blood. Free T4 is considered more accurate because it’s the portion that is active/unbound.
• T3 (Sometimes Free T3): Because T3 is the active hormone, measuring it can give better insight into how much hormonal “power” your body actually has, especially if symptoms exist but TSH and T4 look “normal.”
• Other factors: Sometimes conversion of T4 to T3 is impaired (for example, due to illness, stress, nutrient deficiencies like selenium), so a “normal” T4 might not translate to enough active T3.

Because of these dynamics, thyroid panels are often more informative than single tests. Endocrinologists and functional medicine practitioners use combinations of TSH, free T4, free T3 (and sometimes reverse T3) to get a full picture. 

When to Seek Help or When to Consult a Specialist

Thyroid problems can sneak in slowly. Because thyroid hormones influence so many systems, subtle symptoms might be attributed to stress, diet, or aging. But these signs deserve attention:

• Sudden, unexplained weight loss or gain
• Persistent fatigue, cold intolerance, or inability to stay warm
• Palpitations, irregular heartbeat, tremors, anxiety, mood swings
• Hair loss, brittle nails, dry skin, changes in skin texture
• Digestive issues — constipation, frequent bowel movements, changes in appetite
• Sleep disturbances (insomnia, restless sleep, insomnia)
• Changes in menstrual cycle (for women), fertility problems, mood instability

If you experience a combination of these or if symptoms persist despite healthy lifestyle choices, consider getting a thyroid panel (TSH, free T4, free T3) and consult an endocrinologist or integrative medicine specialist like Integrative Wellness Centers.

If you suspect thyroid issues or if you’ve had lab tests but still feel unwell, our team can help make sense of the bigger picture and craft a personalized plan for restoring balance.

Ready to take control of your thyroid health? 👉 Schedule an appointment with Integrative Wellness Centers today.

📞 Take Action: When & Why to See a Specialist

If you recognize several of the red-flag symptoms above, or if you suspect hormonal or metabolic imbalance, don’t wait. Early detection and intervention can restore balance before long-term complications arise.

At Integrative Wellness Centers, we take a complete-body, root-cause approach: assessing thyroid function, hormonal balance, gut health, nutrient status, and lifestyle factors, to tailor a plan that supports your unique needs. Book a comprehensive thyroid & wellness consultation today.

Common Questions & Misconceptions About Thyroid Hormones

1. What are the 4 hormones of the thyroid gland?
As outlined above: T4, T3, TSH (from pituitary), and calcitonin.

2. What is the main difference between T3 and T4?
T4 is a prohormone — relatively inactive and longer-lasting. T3 is active and much more potent, influencing metabolism, energy, heart rate, and more.

3. Which is more important, T3, T4 or TSH?
They all matter. TSH regulates the system. T4 is the main product and reserve. T3 is the active hormone. A full thyroid panel (TSH + free T4 + free T3) is often needed for accurate assessment.

4. What happens if T4 is too high?
Elevated T4 (especially free T4) may lead to thyrotoxicosis — symptoms include rapid heartbeat, weight loss, increased bowel movements, tremors, anxiety, heat intolerance.

5. Does high T4 cause weight gain?
Unlikely. High T4 generally increases metabolism — leading more often to weight loss despite increased appetite. 

6. How do T3 and T4 affect the body?
They regulate metabolism, energy production, heart rate, body temperature, digestive speed, mood, skin/hair/nail health — virtually every major system.

7. Can stress affect T3, T4 and TSH levels?
Yes. Stress (along with illness, severe diet changes, nutrient deficiencies) can interfere with T4-to-T3 conversion, altering active hormone levels despite “normal” lab values. 

8. What should I avoid if my T4 is high?
While diet alone won’t “cure” hyperthyroidism, excessive iodine intake may worsen overactive thyroid (since iodine is raw material for hormone production). It’s best to follow a healthcare provider’s guidance.

9. Does thyroid imbalance affect sleep, mood, or digestion?
Absolutely. Overactive thyroid may lead to insomnia, anxiety, restlessness, and frequent bowel movements. Underactive thyroid may cause fatigue, depression, constipation, sluggish digestion, cold intolerance.

10. How often should you get your thyroid checked?
If you’re symptomatic or have risk factors (family history, autoimmune conditions, other endocrine disorders), yearly — or as advised by your healthcare provider. If on therapy (e.g., thyroid hormone replacement), follow-up may be more frequent.