Hashimoto's and Anxiety: Is There a Link Between the Thyroid and Mental Health?

She had already been in psychiatric care for two years when she came to my office in Campinas. Generalized anxiety, a racing heart at rest, insomnia, a constant feeling of being "on edge" — all well documented, all treated with the right medication at the right dose. But the physical symptoms that came along with it — cold intolerance, dry skin, irregular menstrual cycles — had never been looked into in depth. Her anti-TPO, ordered for the first time at that visit, came back far above the reference range.

This kind of scenario isn't rare. And it raises a legitimate question that many patients ask and seldom get a complete answer to: is there really a link between the thyroid — especially Hashimoto's thyroiditis — and mental health? The answer, backed by scientific evidence, is yes, and it's worth understanding why.

When anxiety has a hidden thyroid piece

Anxiety has many causes, and it would be a mistake to blame every case of anxiety on the thyroid. But it's also a common — and frequent — mistake to exhaustively investigate the psychological and social side of an anxiety disorder without ever asking about the thyroid, especially when there are associated physical symptoms that anxiety alone doesn't explain well: intolerance to cold or heat, weight changes, hair loss, menstrual changes, disproportionate fatigue.

The thyroid regulates the metabolism of virtually every cell in the body, including the neurons and brain circuits involved in regulating mood and the stress response. That's why both hypothyroidism and hyperthyroidism have well-described psychiatric symptoms in the medical literature — but what more recent research has been highlighting is something more: it isn't only the hormone level that matters. The autoimmune process itself, present in Hashimoto's thyroiditis, appears to play an independent role.

What science shows about thyroid autoimmunity and psychiatric symptoms

A meta-analysis published in JAMA Psychiatry, led by Siegmann and colleagues, pooled a number of studies on the topic and found a significant association between autoimmune thyroiditis (the presence of thyroid antibodies) and a higher risk of anxiety and depressive disorders — including in people whose thyroid function was still within the range considered normal (biochemical euthyroidism).

This finding matters because it shifts the focus from "only TSH matters" to a broader question: is there an underlying inflammatory and autoimmune process that, on its own, can influence the brain circuits tied to mood and anxiety, regardless of whether the person already shows overt hypothyroidism on their labs?

Hashimoto's can cause symptoms even with "normal" hormones

This point ties directly into what we discussed in an earlier article in this series about a "normal" TSH and persistent symptoms. A study published in the journal Thyroid, led by Ott and colleagues, compared women with Hashimoto's thyroiditis to women without the disease and found a higher symptom burden — including psychological symptoms such as anxiety, as well as physical complaints — in the patients with Hashimoto's, even when their thyroid hormones were within the reference range.

In other words: the presence of the autoimmune disease, by itself, already seems to be associated with more symptoms experienced by the patient, regardless of the hormone status measured in the blood at that moment. This helps explain why so many women with Hashimoto's report anxiety, mood swings, and a vague sense of "not feeling well," even when their endocrinologist says their labs are under control.

Why thyroid-related anxiety is often treated as purely "psychological"

In clinical practice, this scenario is common: the patient seeks help for anxiety and is referred — appropriately — for psychological care and, when needed, psychiatric care. The treatment works partially, but residual physical symptoms persist. Rarely does anyone stop at that point to systematically ask about thyroid function and thyroid antibodies, because the initial complaint was categorized as "psychiatric" and followed that path in isolation.

Not all anxiety is "just anxiety" — sometimes it's the body signaling that an underlying inflammatory process needs to be investigated too.

This doesn't mean psychological or psychiatric treatment is wrong — on the contrary, it's usually necessary and effective. It means that when there are associated physical signs, it's worth adding a thyroid evaluation to the care already underway, instead of treating the two as completely separate compartments.

How functional clinical reasoning approaches this overlap

Functional Integrative Health aims for exactly this kind of integration: bringing together the patient's psychiatric and emotional history with a complete thyroid workup — TSH, free T3, thyroid antibodies — and other markers that may be contributing to the picture, such as low-grade inflammation, sleep, and chronic stress. The goal isn't to replace mental health care, but to add a piece that, when present, is usually left out of the equation.

This reasoning does not propose stopping or replacing psychiatric medication based on a thyroid test alone. It proposes investigating, methodically and carefully, whether a thyroid component is contributing to the picture, and managing that finding — once confirmed — together with whoever is already caring for the patient's mental health.

When it's worth checking the thyroid in anxiety

Some signs strengthen the case for checking the thyroid in patients with anxiety: associated physical symptoms (intolerance to cold or heat, weight changes, hair loss, menstrual changes), a family history of thyroid or autoimmune disease, only a partial response to well-managed psychiatric treatment, and worsening during periods of greater hormonal vulnerability, such as postpartum or perimenopause.

In these cases, the most effective path is to add — not substitute — a complete thyroid evaluation to the existing mental health care, so the full picture comes into view.

Individualization is the key

Anxiety is a complaint that calls for careful investigation, and it rarely has a single cause. Recognizing that the thyroid, especially in the autoimmune form of Hashimoto's thyroiditis, can be a relevant piece of this puzzle — even when hormone levels look normal — is an important step toward more complete care, without replacing the mental health support already in place.

In the next article in this series, we'll cover a more practical topic: how to choose a doctor to treat Hashimoto's and hypothyroidism, and what to look for to make sure you get a truly complete evaluation.