Yes, thyroid problems can trigger seizures, though the risk varies dramatically depending on whether your thyroid is overactive or underactive. When thyroid hormone levels become imbalanced, they disrupt the electrical stability of your brain by lowering your "seizure threshold," the level of resistance your brain has against abnormal electrical discharges. This connection is particularly strong in hyperthyroidism and in a rare autoimmune condition called Hashimoto's encephalopathy, where the immune system attacks thyroid tissue and simultaneously triggers neurological symptoms.

How Does Your Thyroid Control Brain Electrical Activity?

Your thyroid gland acts as your body's master thermostat, producing two primary hormones: Thyroxine (T4) and Triiodothyronine (T3). These hormones tell every cell in your body how much energy to use and how fast to work. Your brain is one of the most energy-demanding organs, relying on a precise balance of thyroid hormones to maintain stable electrical function. When thyroid hormone levels swing too high or too low, the brain's neurons become either overstimulated or undersupported, making seizures more likely to occur.

To understand this connection, it helps to know what the key thyroid markers mean. When you get a thyroid blood test, you'll see several measurements that paint a picture of your thyroid health:

• TSH (Thyroid Stimulating Hormone): This is the signal your brain's pituitary gland sends to your thyroid. High TSH means your thyroid is underperforming and your brain is "shouting" for more hormone. Low TSH means your thyroid is overactive and your brain is telling it to slow down.
• Free T4 (Thyroxine): This is the storage form of thyroid hormone circulating in your blood, waiting to be converted into the active form your cells can use.
• Free T3 (Triiodothyronine): This is the active fuel that your cells actually use to create energy and maintain electrical stability in the brain.

Why Does an Overactive Thyroid Increase Seizure Risk?

Hyperthyroidism, or an overactive thyroid, poses a much greater seizure risk than an underactive thyroid. When your thyroid gland pumps out excessive hormone, a state called thyrotoxicosis, your entire nervous system goes into overdrive. Excessive Free T3 acts as a stimulant to your central nervous system, increasing the "excitability" of your brain's neurons. If neurons become too excited and fire off electrical signals in an uncontrolled burst, a seizure can occur.

Clinical research shows that people with hyperthyroidism have a nearly twofold increased risk of developing epilepsy compared to those with healthy thyroid function. While seizures are not a common everyday symptom of hyperthyroidism, they are a documented neurological complication that becomes more likely as hormone levels climb.

In the most severe cases, hyperthyroidism can escalate into a life-threatening emergency called a thyroid storm or thyrotoxic crisis. This happens when thyroid hormone levels become dangerously high, often triggered by major stressors like surgery, infection, or trauma in someone with an already overactive thyroid. During a thyroid storm, the brain is essentially flooded with T3, which can lead to delirium, coma, and seizures. This is why managing thyroid health is critical; it ensures hormone levels stay within a safe range and prevents these extreme escalations.

What About an Underactive Thyroid and Seizures?

An underactive thyroid, or hypothyroidism, can also play a role in seizures, but only in extreme circumstances. In hypothyroidism, your body slows down dramatically. You might feel heavy, cold, and mentally sluggish. In very severe, untreated cases, this can lead to myxoedema coma, a state of extreme metabolic depression where electrolyte imbalances, such as low sodium, or reduced oxygen to the brain can trigger seizure activity.

For the average person with mild hypothyroidism, seizures are highly unlikely. However, the brain fog and cognitive slowing associated with low thyroid levels can sometimes be mistaken for the confusion that follows a seizure, known as the post-ictal state. This is why a thorough clinical review with a doctor is essential to distinguish between different types of neurological and metabolic symptoms.

What Is Hashimoto's Encephalopathy and How Does It Cause Seizures?

Perhaps the most direct link between thyroid markers and seizures is a rare condition called Hashimoto's encephalopathy. Despite its name, this condition is not actually caused by an underactive thyroid itself, but rather by the immune system's confusion. In Hashimoto's thyroiditis, your body produces antibodies that attack the thyroid gland. In Hashimoto's encephalopathy, these same antibodies are found in high levels alongside neurological symptoms like confusion, memory loss, and seizures.

The two key antibodies involved in Hashimoto's encephalopathy are Thyroid Peroxidase Antibodies (TPOAb) and Thyroglobulin Antibodies (TgAb). TPOAb indicates that your immune system is targeting an enzyme used to make thyroid hormones, while TgAb targets the protein where thyroid hormones are stored. When these antibodies reach high levels, they can trigger inflammation and electrical instability in the brain, leading to seizures and other neurological symptoms.

How to Clarify Your Thyroid Status and Neurological Symptoms

• Consult Your GP First: Before pursuing specialized testing, speak with your primary care doctor to rule out other common causes of seizures or neurological symptoms. Your doctor can assess your medical history and determine whether thyroid testing is appropriate.
• Track Your Symptoms and Lifestyle: Keep a detailed log of when symptoms occur, what you were doing, what you ate, and how you felt. Note any patterns related to stress, sleep, exercise, or other lifestyle factors that might influence seizure threshold or thyroid function.
• Request Comprehensive Thyroid Testing: Ask your doctor for a full thyroid panel that includes TSH, Free T4, Free T3, and thyroid antibody tests (TPOAb and TgAb). This comprehensive approach provides a clearer picture than TSH alone and can help identify autoimmune thyroid conditions like Hashimoto's.
• Discuss Results With Your Doctor: Once you have your results, review them with your healthcare provider to understand what your specific numbers mean and whether they explain your neurological symptoms.

The key takeaway is that thyroid dysfunction and seizures are connected through the brain's electrical stability. Hyperthyroidism poses the greatest risk, increasing seizure likelihood through excessive neural stimulation. Hashimoto's encephalopathy, though rare, creates a direct autoimmune link between thyroid antibodies and seizure activity. If you're experiencing unexplained seizures or neurological symptoms alongside signs of thyroid dysfunction, comprehensive thyroid testing and a conversation with your doctor can provide the clarity needed to address the underlying cause.