One small gland, two directions it can go wrong.
The National Library of Medicine describes the thyroid as a small, butterfly-shaped gland in the front of the neck making hormones that control how the body uses energy. Those hormones reach nearly every organ, affecting breathing, heart rate, weight, digestion, and mood.
Trouble runs in two directions. The National Institute of Diabetes and Digestive and Kidney Diseases defines hypothyroidism as the thyroid not making enough hormone for the body's needs, which slows things down: fatigue, weight gain, feeling cold, aching joints and muscles, dry skin or thinning hair, irregular periods, a slowed heart rate, depression. Hyperthyroidism is the opposite, and the same institute lists nervousness, irritability, trouble sleeping, fatigue, shaky hands, and muscle weakness.
Notice that fatigue sits on both lists. The direction is not something you can read off your symptoms.
Where these conditions usually come from.
In the United States, NIDDK names Hashimoto's disease — an autoimmune disorder — as the most common cause of hypothyroidism. It has its own guide here, because it deserves more than a paragraph. Other causes include thyroiditis, congenital hypothyroidism, surgical removal of thyroid tissue, radiation treatment, and certain medicines for heart conditions, bipolar disorder, and cancer. Iodine deficiency and pituitary disorders are less common.
Graves' disease is the most common cause of hyperthyroidism and is also autoimmune; NIDDK notes it is more common in women and in people older than 30. Overactive nodules, thyroiditis, too much iodine, and too much thyroid hormone medicine can also push levels high.
The Office on Women's Health reports that women are more likely than men to have thyroid disease, and that one in eight women will develop thyroid problems during her lifetime. It notes these diseases are especially prevalent right after pregnancy and after menopause, and that the symptoms are sometimes mistaken for menopause.
The part that gets mistaken for something else.
NIDDK makes a pointed observation about older adults: hyperthyroidism is sometimes mistaken for depression or dementia. That is worth sitting with. A treatable hormone problem can wear the face of a neurological one.
The research on hypothyroidism and thinking is real but more measured than the internet suggests. A 2021 integrative review in the Journal of Neuroendocrinology found impaired verbal memory to be the most consistently reported cognitive difficulty in overt hypothyroidism, and reported that cognitive and behavioural symptoms can improve with thyroid hormone treatment, though some studies found difficulties that remained. Where levels are only mildly off, the same review calls the evidence conflicting: large population studies show no impairment, smaller studies using sensitive tools do, and the authors ask for long-term research rather than declaring it settled.
A link exists, it is documented, and it is not a formula. Cognitive symptoms do not confirm a thyroid cause, and a thyroid diagnosis does not explain every cognitive symptom you have.
How clinicians actually check, and who steers treatment.
NIDDK is blunt that a hypothyroidism diagnosis cannot be based on symptoms alone; it comes from history, a physical exam, and testing. The blood tests it describes: TSH, the pituitary hormone that tells the thyroid how much T4 and T3 to make; T4, where many professionals prefer the free T4 measure; T3, used when T4 reads normal but hyperthyroidism is still suspected; and antibody tests, which may help diagnose an autoimmune thyroid disorder such as Hashimoto's or Graves'. Imaging may also be part of the evaluation.
If you feel unwell and were told your thyroid is normal, ask which of those tests were run and which were not — antibody testing and T3 are not always part of a basic panel. That is a fair question to put to the clinician managing your thyroid.
Treatment stays with a prescriber. NIDDK describes levothyroxine for hypothyroidism, dosing adjusted by blood tests around six to eight weeks and yearly once stable, and antithyroid medicines, radioiodine therapy, or surgery for hyperthyroidism. Untreated, it warns, hyperthyroidism can cause serious problems including an irregular heartbeat that can lead to blood clots, stroke, and heart failure. No diet or supplement described anywhere substitutes for that care.
- Which thyroid tests have I had — TSH only, or T4, T3, and antibodies as well?
- Have thyroid antibodies ever been checked, and what did they show?
- Could any medicine I take be affecting my thyroid or my test results?
- If my levels are being treated and I still feel foggy, what else are we looking at?
If you want to ask about care here.
Gates Brain Health is a functional neurology practice in Reno, Nevada, led by Dr. Randall Gates, D.C., DACNB, and its published focus includes Hashimoto's thyroiditis alongside other chronic neurological concerns. Your thyroid hormone stays with the clinician who prescribes it. Nothing here replaces that relationship, your primary care provider, an endocrinologist, or emergency care, and whether this practice fits your situation is settled by an evaluation, not by a web page.
The practice publishes a free consultation as a first step; what an examination involves lives on the treatment page rather than here. To ask about one, call (775) 507-2000, Monday through Friday, 8:00 AM to 5:00 PM, or use the secure contact form for a general, non-medical message or callback request. Online scheduling is not available.
One emergency note, because of the heart risk above: MedlinePlus says that if you think you or someone else is having a stroke — face drooping, arm weakness, slurred speech, sudden numbness or confusion — call 911 right away.