Quick Answer
Hypothyroidism causes brain fog, depression and memory problems; hyperthyroidism causes anxiety and tremor. A simple blood test reveals thyroid problems.
Medically reviewed by Dr. Jitendra Prasad Yadav • NMC 8029 • Kathmandu Neurology Clinic & Cognitive Center
Your thyroid — a butterfly-shaped gland in your neck — produces hormones that regulate metabolism throughout your body, including the brain. Thyroid disorders are common and frequently cause neurological and psychiatric symptoms that are mistaken for primary brain or mood disorders.
How thyroid hormones affect the brain
Thyroid hormones (T3 and T4) regulate brain development, neurotransmitter function, and neuronal metabolism. The brain has high concentrations of thyroid hormone receptors. When thyroid function is abnormal, brain function is affected — causing symptoms that range from subtle cognitive slowing to severe mood disorders.
Hypothyroidism — underactive thyroid
When the thyroid produces too little hormone, everything slows down:
- Fatigue and lethargy
- Depression and low mood
- Memory problems and 'brain fog'
- Cold intolerance
- Weight gain
- Constipation
- Dry skin and hair loss
- Slow heart rate
- Muscle weakness and cramps
- Heavy menstrual periods
Hyperthyroidism — overactive thyroid
When the thyroid produces too much hormone, everything speeds up:
- Anxiety and irritability
- Insomnia
- Tremor (especially of hands)
- Rapid heartbeat and palpitations
- Weight loss despite increased appetite
- Heat intolerance
- Frequent bowel movements
- Muscle weakness (especially thighs)
- Eye changes (bulging, irritation)
Diagnosis and treatment
Diagnosis is a simple blood test measuring TSH (thyroid stimulating hormone), with T3 and T4 for confirmation. Hypothyroidism is treated with levothyroxine (synthetic T4) — usually a daily pill, well-tolerated with proper dosing. Hyperthyroidism is treated with antithyroid medications, radioactive iodine or surgery. Both conditions are highly treatable — but symptoms may take weeks to months to fully resolve.
When to get tested
If you have unexplained fatigue, mood changes, cognitive problems, tremor, weight changes, or any combination of symptoms above — ask your doctor for a thyroid test. At Kathmandu Neurology Clinic, thyroid function is checked when symptoms suggest it, because thyroid disorders can mimic or worsen neurological and psychiatric conditions.
When to seek professional evaluation
Thyroid testing is simple and inexpensive — if you have neurological or psychiatric symptoms, it's worth checking.
This guide is educational and does not replace individual medical advice.
Frequently asked questions
Answers reviewed by Dr. Jitendra Prasad Yadav • MBBS, MD (Internal Medicine), FICN (Neurology), FCNV, FIHM • NMC 8029
Brief slips without functional impact are often benign; persistent, progressive interference with daily tasks warrants assessment.
Yes, anxiety, depression, and poor sleep frequently impair attention and recall and improve when treated.
Normal worry is proportional, time-limited, and about specific issues. In GAD, worry is excessive, persistent, and about multiple topics, and it causes significant distress or functional impairment.
Yes. CBT and SSRIs/SNRIs are effective treatments with response rates of 50-70%. Many individuals achieve substantial symptom reduction with appropriate care.
More: All FAQs → · Ask Dr. Jitendra →
Related articles
Probiotics and Mental Health: What the Evidence Actually Shows
Do probiotics really improve mood and anxiety? An honest review of the evidence, which strains have data, and when probiotics are actually useful.
Vitamin B12 Deficiency and Nerve Health: Symptoms, Causes and Treatment
B12 deficiency causes tingling, numbness, fatigue and cognitive problems — and it's easily treatable when caught early. Learn the symptoms, who is at risk and how it's diagnosed.
Understanding Lab Tests: B12, Thyroid and What Your Numbers Mean
A plain-language guide to common blood tests — B12, thyroid function, HbA1c, vitamin D — what they measure and what abnormal results mean.
Medical Disclaimer
Content on this website is for general educational purposes only and does not constitute medical advice, diagnosis, or treatment. It is not a substitute for evaluation by a qualified healthcare professional. Always seek the advice of your physician or other qualified provider with any questions regarding a medical condition. Never disregard professional medical advice or delay seeking it because of something you have read on this website. In case of a medical emergency, contact emergency services immediately. No doctor–patient relationship is established by use of this site or by contacting the clinic through the site.
References & Review
Reviewed by Dr. Jitendra Prasad Yadav • Last reviewed: 2026-11-10
- International Classification of Headache Disorders, 3rd edition (ICHD-3).
- Harrison's Principles of Internal Medicine — Neurology sections.
- American Academy of Neurology guidelines for selected conditions (where applicable).
Content is educational and aligns with standard medical references; individual evaluation may vary. External links provide context and do not imply endorsement.