Headaches are so common that most people accept them as an ordinary part of life. But when they are frequent, severe, or simply unresponsive to the usual remedies, they deserve a closer look — and the thyroid is one explanation that is all too often overlooked. If you have been wondering whether an underactive thyroid can cause headaches, the evidence increasingly suggests it can. Research published across multiple peer-reviewed journals has identified a meaningful and potentially bidirectional relationship between hypothyroidism and headache disorders — including migraine — that warrants proper investigation rather than assumption.
What Does the Research Say?
The link between an underactive thyroid and headaches is better supported by evidence than many people — and indeed many clinicians — realise. A 2025 systematic literature review published in PMC, which analysed 29 relevant studies using PRISMA guidelines, concluded that migraine and disturbed thyroid function may influence one another, with a positive correlation between hypothyroidism — particularly Hashimoto’s thyroiditis — and migraine demonstrated across multiple studies.
One of the most compelling pieces of evidence comes from a large longitudinal study that followed over 8,400 participants for more than twenty years. The researchers found that people with pre-existing headache disorders had a 21% higher risk of developing new-onset hypothyroidism — and for those specifically with migraine, that elevated risk rose to 41%. A separate study of 102 patients with newly diagnosed hypothyroidism found that around 30% developed a new headache disorder within two months of their thyroid diagnosis.
Perhaps most striking is the treatment evidence. A study examining headache patterns in hypothyroid patients found that levothyroxine treatment — standard thyroid hormone replacement — relieved headaches in 78% of participants, directly implicating the thyroid hormone deficiency as the driving mechanism. This is clinically significant: it suggests that for a meaningful proportion of people with persistent headaches and an underactive thyroid, treating the thyroid is treating the headache.
A 2019 case-control study published in Cephalalgia found that the prevalence of migraine was substantially elevated in patients with subclinical hypothyroidism — where TSH is only mildly raised and many patients have no obvious symptoms — compared with healthy controls. This finding is particularly relevant because subclinical hypothyroidism is frequently missed on basic TSH testing, meaning the thyroid connection is never identified.
What Types of Headache Does Hypothyroidism Cause?
Not all thyroid-related headaches look the same. Research has identified two main patterns, and understanding the difference can help you recognise whether your headaches might fit the picture:
Headache Attributed to Hypothyroidism (HAH)
This is the headache type formally recognised by the International Classification of Headache Disorders (ICHD-3) as directly caused by hypothyroidism. It is typically described as bilateral — affecting both sides of the head — and non-pulsatile, meaning it presents as a pressure or tightening sensation rather than a throbbing pain. It tends to be diffuse rather than localised, and in some cases persists even after thyroid hormone levels are corrected, though its frequency and severity typically reduce with treatment.
Migraine
Research has also identified a significant association between hypothyroidism and migraine — a distinctly different type of headache characterised by unilateral (one-sided), pulsatile (throbbing) pain, often accompanied by nausea, vomiting, or sensitivity to light and sound. A study published in PMC found that 92% of headaches in hypothyroid patients were more consistent with migraine than with the classic HAH pattern — suggesting that the thyroid-headache connection may express itself as migraine far more commonly than previously understood.
A patient seen at our Birmingham clinic — a woman in her early thirties who had been managing increasingly frequent migraines for over a year — had tried three different preventive medications with only partial benefit. When we carried out a comprehensive private thyroid blood test including TSH, free T3, free T4, and thyroid antibodies, her results revealed elevated TPO antibodies and a TSH at the upper end of the normal range — consistent with early Hashimoto’s thyroiditis. Following initiation of appropriate treatment, her migraine frequency reduced considerably over the subsequent three months.
Why Does Hypothyroidism Cause Headaches? The Mechanisms
Several biological pathways are thought to connect an underactive thyroid with headache and migraine, and in most cases it is a combination of mechanisms rather than a single cause:
Vascular Dysregulation
Thyroid hormones help regulate the tone of blood vessels — the degree to which they contract and dilate. When thyroid hormone levels are low, this vascular regulation is disrupted. Blood vessels may dilate or constrict abnormally, in a pattern that resembles the vascular changes thought to contribute to migraine. Researchers believe this vascular dysregulation may be one of the primary mechanisms linking hypothyroidism to both tension-type headaches and migraine.
Serotonin Disruption
Serotonin — the neurotransmitter most closely linked to migraine pathophysiology — is directly regulated by thyroid hormones. Hypothyroidism reduces serotonin activity, which lowers the threshold at which the trigeminal nerve system — the pain pathway involved in migraine — becomes activated. This is why migraine in hypothyroid patients can become more frequent and more severe as thyroid function declines, and why restoring hormone levels often reduces migraine burden.
Fluid Retention and Tissue Swelling
Hypothyroidism causes fluid retention and a condition called myxoedema, in which tissues accumulate mucopolysaccharides — substances that draw water into the surrounding tissue. This swelling can affect tissues around the brain and cranial nerves, potentially contributing directly to headache symptoms. The improvement in headaches seen with levothyroxine treatment partly reflects the reduction in this fluid accumulation as hormone levels normalise.
Reduced Cerebral Metabolism
The brain is an extraordinarily metabolically active organ, and it is highly sensitive to reductions in thyroid hormone availability. When thyroid hormone levels fall, cerebral energy metabolism slows, affecting neuronal function and potentially contributing to the neurological sensitivity that underlies both migraine and tension-type headache. Brain fog, cognitive slowing, and headaches in hypothyroidism may therefore share a common metabolic root.
Sleep Disruption
Hypothyroidism is associated with significantly higher rates of obstructive sleep apnoea and poor sleep quality — both of which are well-established triggers for headache and migraine. Where poor sleep is both a symptom of the thyroid condition and a driver of headache, the two problems reinforce each other in a cycle that only effective thyroid treatment can fully interrupt.
Could It Be Subclinical Hypothyroidism?
One of the most important — and underappreciated — aspects of the thyroid-headache connection is that it appears to operate even at the subclinical level. Subclinical hypothyroidism, where TSH is mildly elevated but T3 and T4 remain within the normal range, is a condition that many patients are told requires no treatment. Yet the 2019 Cephalalgia case-control study found that migraine prevalence was substantially higher in subclinical hypothyroid patients compared with matched controls — suggesting that even mild thyroid insufficiency carries real neurological consequences.
This is precisely why a basic TSH test alone may not tell the full story for someone experiencing persistent headaches. A comprehensive private thyroid blood test covering TSH, free T3, free T4, and thyroid antibodies provides a much more complete picture — and may identify a subclinical thyroid issue that a standard check would miss entirely.
Other Thyroid Symptoms to Look Out For
Headaches rarely appear in isolation when the thyroid is involved. If your persistent headaches are accompanied by any of the following, thyroid assessment is strongly worth considering:
- Persistent fatigue or exhaustion that does not improve with sleep
- Unexplained weight gain or difficulty losing weight
- Feeling cold when others around you are comfortable
- Dry skin, brittle nails, or thinning hair
- Low mood, brain fog, or difficulty concentrating
- Constipation or slowed digestion
- Puffiness around the eyes or face
- A slow heart rate or low blood pressure
- Heavy, irregular, or more painful periods
The more of these features accompany your headaches, the stronger the case for thyroid investigation. At The Private GP in Birmingham, our GMC-registered doctors can assess your full clinical picture and arrange same-day blood testing where appropriate. If you would like to get to the bottom of what is driving your headaches, a face-to-face GP consultation is the most thorough and efficient way to start.
Will Thyroid Treatment Improve My Headaches?
For many people, yes — and the evidence behind this is encouraging. The study demonstrating levothyroxine relieved headaches in 78% of hypothyroid patients is one of the most clinically meaningful findings in this area, suggesting that treating the underlying thyroid condition can be one of the most effective headache interventions available — particularly for those who have not responded well to conventional headache management.
It is worth noting that the full benefit of thyroid treatment on headache frequency and severity may take several months to become apparent, as hormone levels gradually stabilise and the underlying biological disruptions begin to resolve. For some people — particularly those with a longstanding pattern of migraine that preceded the thyroid diagnosis — additional headache management may be needed alongside thyroid treatment. However, the combination is typically more effective than either approach in isolation.
Frequently Asked Questions
- How do I know if my headaches are caused by my thyroid?
There is no single defining feature that distinguishes thyroid headaches from other types — which is precisely why proper testing matters. The strongest indicators are headaches that are persistent, have worsened over time, do not respond well to standard treatments, and are accompanied by other hypothyroid symptoms such as fatigue, weight gain, cold intolerance, or hair thinning. A comprehensive thyroid blood test including TSH, free T3, free T4, and thyroid antibodies is the most reliable first step towards an answer.
- Can subclinical hypothyroidism cause migraines?
Research suggests it can. A case-control study published in Cephalalgia found that migraine prevalence was significantly higher in patients with subclinical hypothyroidism — where TSH is mildly elevated but hormone levels appear normal — compared with matched healthy controls. This underlines the importance of a comprehensive thyroid panel rather than a basic TSH check alone when investigating headache disorders.
- What type of headache does hypothyroidism cause?
Hypothyroidism can produce two main types of headache: headache attributed to hypothyroidism (HAH), which is typically bilateral, non-pulsatile, and diffuse — often described as a pressure sensation; and migraine, which is unilateral, throbbing, and may be accompanied by nausea and light sensitivity. Research has found that migraine-type headaches are more common in hypothyroid patients than the classical HAH pattern, accounting for the majority of thyroid-associated headaches in some study populations.
- Will levothyroxine help my headaches?
For those whose headaches are linked to hypothyroidism, evidence suggests it can. A study of hypothyroid patients found that levothyroxine treatment relieved headaches in 78% of participants. Improvement may take several weeks to months as thyroid hormone levels stabilise. It is important not to adjust thyroid medication independently in an attempt to manage headaches — any dose changes should be guided by a GP based on blood test results and clinical assessment.
- Do I need a GP referral to get a thyroid blood test in Birmingham?
No. At The Private GP, you can access a private thyroid test without a referral, with same-day results and full GP interpretation included. A comprehensive panel covering TSH, free T3, free T4, and thyroid antibodies gives a far more complete picture than a standard TSH check — and is the most reliable way to identify whether your thyroid is contributing to your headaches.