Thyroid: Hypothyroidism and Hyperthyroidism Explained
This small gland that regulates everything.
Dr. Marc Dufresne
Endocrinologist
In simple terms
Thyroid dysfunctions affect 10% of the population, with a female predominance. Symptoms, diagnosis, and treatments.
What you need to remember
- Hyperthyroidism (overactive thyroid) — Weight loss despite preserved appetite
The thyroid is a butterfly-shaped gland located at the base of the neck. It produces T3 and T4 hormones, which regulate the metabolism of almost all body cells.
Hypothyroidism (underactive thyroid)
Symptoms
- Persistent fatigue
- Weight gain despite normal eating
- Excessive sensitivity to cold
- Constipation
- Dry skin, brittle hair
- Intellectual slowdown, memory problems
- Depression
Most frequent cause
Hashimoto's thyroiditis: an autoimmune disease where the immune system attacks the thyroid.
Treatment
Levothyroxine (synthetic thyroid hormone) for life, with dose adjustment according to TSH.
Hyperthyroidism (overactive thyroid)
Symptoms
- Weight loss despite preserved appetite
- Palpitations, tachycardia
- Nervousness, irritability, tremors
- Heat intolerance, excessive sweating
- Diarrhea
- Insomnia
Most frequent cause
Graves' disease: an autoimmune disease stimulating the thyroid.
Treatments
- Antithyroid drugs (carbimazole, propylthiouracil)
- Radioactive iodine
- Surgery (thyroidectomy)
When to check your thyroid?
- Persistent unexplained fatigue
- Weight variation without lifestyle change
- Mood disorders resistant to treatment
- Family history of thyroid disease
- Postpartum (postpartum thyroiditis)
A simple TSH test is enough to screen for thyroid dysfunction. It is an inexpensive and very informative routine examination.
The words explained
Medical terms used above, in everyday language.
- Symptom
- A sign you can feel or see that something is wrong, like pain, tiredness or a rash.
- Hormone
- A chemical messenger made by your body that tells organs what to do.
- Metabolism
- How your body turns food into energy and builds or repairs itself.
- Immune system
- Your body's defence team: cells that fight germs and repair damage.
When should you see a doctor?
- Your symptoms last more than a few weeks or keep coming back.
- They get worse quickly, or stop you doing everyday things.
- You notice sudden pain, breathing trouble, fainting or bleeding — seek urgent care.
- You already take medication and want to change anything about it.
This article explains general health information. It does not replace advice from your own doctor.
Frequently asked questions
- What is Thyroid: Hypothyroidism and Hyperthyroidism Explained?
- Thyroid dysfunctions affect 10% of the population, with a female predominance. Symptoms, diagnosis, and treatments.
- What are the main symptoms or signs of Thyroid: Hypothyroidism and Hyperthyroidism Explained?
- Common signs vary from person to person. The article above lists the symptoms to watch for, how they progress, and when they need medical attention.
- When should you see a doctor for Thyroid: Hypothyroidism and Hyperthyroidism Explained?
- See a doctor if symptoms last more than a few weeks, get worse quickly, stop you doing everyday things, or if you notice sudden pain, breathing trouble, fainting or bleeding.
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