Hyperthyroidism and Graves' Disease: Why Is My Heart Racing While I Lose Weight?

A racing heart with weight loss, even when you are eating normally, is a classic pattern of hyperthyroidism, in which the thyroid makes more hormone than your body needs. Graves' disease, an autoimmune condition, is a common cause. Treatment is available and outcomes are often good, but chest pain, fainting, or confusion with a high fever needs emergency care. This article covers hyperthyroidism and Graves' disease: why the heart speeds up, how it is tested, treatment options, eye and pregnancy concerns, and when to get help.

Hyperthyroidism and Graves' disease: what is happening in your body

Your thyroid is a small gland at the front of your neck. It releases hormones that help set the pace of many body systems, including heart rate, body temperature, digestion and how quickly you use energy. According to MedlinePlus from the National Institutes of Health, hyperthyroidism is the condition in which the thyroid makes too much of these hormones.

Graves' disease is an autoimmune cause. The immune system makes antibodies that act on the thyroid like a switch stuck in the on position, so the gland keeps producing hormone without the usual feedback signals. Why some people develop these antibodies is not fully understood. Several factors, including genetics and other autoimmune conditions, are thought to contribute.

Graves' disease is not the only reason for an overactive thyroid. Other causes include one or more overactive thyroid nodules (sometimes called toxic nodular goiter), inflammation of the thyroid that releases stored hormone (thyroiditis), and taking too much thyroid hormone medication or excess iodine. A clinician has to sort out which one applies, because the right treatment differs.

Why your heart races while you lose weight

Thyroid hormone acts on the heart and on the body's energy use at the same time, which is why these two symptoms often appear together.

The heart

Excess thyroid hormone can make the heart beat faster and more forcefully. You may notice a pounding pulse, a fluttering in your chest, or a heartbeat you can feel while resting or lying in bed. Some people develop an irregular rhythm called atrial fibrillation. MedlinePlus describes atrial fibrillation as a common type of irregular heartbeat that can raise the risk of blood clots and stroke. We cover that rhythm in its own article on atrial fibrillation, so here the point is only that an overactive thyroid is one of the conditions clinicians look for when it appears.

Over a long period, untreated hyperthyroidism can also strain the heart muscle. A published case report in the National Institutes of Health PubMed Central archive, Graves' disease presenting as bi-ventricular heart failure in a pregnant patient, shows how heart failure can be the first sign in uncommon cases. That is not the usual story, and one case does not predict your course, but it is a reason to take a persistent racing heart seriously.

The weight

Weight loss with hyperthyroidism is linked to a faster metabolism, so the body uses energy more quickly. Appetite often rises too, which is why some people lose weight even while eating more. The full mechanism is not completely understood, and research on the metabolic changes in Graves' disease, including shifts in fat and energy-handling molecules, is ongoing, as in this National Institutes of Health PubMed Central study of acylcarnitine and lipid profiles. Muscle can be lost along with fat, which may leave you feeling weak, especially in the thighs and upper arms.

Other symptoms that can travel with it

Hyperthyroidism can affect many systems, and not everyone has every symptom. Common ones include:

• Feeling hot, sweating more, or being unable to tolerate warm rooms
• Nervousness, irritability, anxiety or trouble sleeping
• A fine shake of the hands (see MedlinePlus on tremor)
• More frequent bowel movements or loose stools
• Lighter or less frequent periods
• Thinning hair and warm, moist skin
• Swelling at the front of the neck (a goiter)

A goiter that grows slowly, with hoarseness or mild trouble swallowing, deserves a same-day or next-available appointment. Trouble breathing, noisy or high-pitched breathing, or neck swelling or swallowing difficulty that is worsening rapidly can mean the airway is being squeezed, and that needs 911 or the emergency room.

Older adults can look different. They may have fewer of the classic complaints and more fatigue, weight loss, low mood, or heart rhythm problems. Because these symptoms overlap with anxiety, menopause and other illnesses, a blood test is how clinicians tell them apart. If weight loss is your main concern, our separate article on causes of unexplained weight loss covers the wider list.

Graves' disease signs beyond an overactive thyroid

Graves' disease can cause problems that other forms of hyperthyroidism do not. The same antibodies may affect tissue around the eyes, a condition often called Graves' eye disease or thyroid eye disease. It can cause gritty or dry eyes, redness, swelling of the eyelids, a staring look, bulging of the eyes, light sensitivity or double vision. A smaller number of people develop thickened skin over the shins.

Eye symptoms can appear before, during or after the thyroid itself is treated, and they do not always track with how high thyroid hormone is. Smoking is associated with a higher chance of eye disease and with worse eye disease, as described in the National Institutes of Health PubMed Central review of Graves' disease, so tell your clinician if you smoke so they can discuss support. That review also describes how much these eye and quality-of-life effects can matter.

Some eye changes are more urgent than others. Sudden vision loss, colors that look faded or dim, or severe eye pain can signal pressure on the optic nerve, a complication of Graves' eye disease that may cause permanent vision loss if it is not treated. These are emergencies: go to the emergency room for same-day eye evaluation. Bulging, grittiness, redness and double vision that is mild or slowly getting worse still deserve a prompt appointment.

How clinicians test for an overactive thyroid

Clinicians combine your history, a physical exam and blood tests. According to MedlinePlus on thyroid tests, the common tests measure thyroid-stimulating hormone (TSH) and thyroid hormones such as free T4 and T3. In hyperthyroidism, TSH is typically low while thyroid hormone is high, though patterns can vary.

To find the cause, your clinician may add one or more of these:

• Blood tests for thyroid-stimulating antibodies, which support Graves' disease
• A radioactive iodine uptake test and scan, which show how the gland takes up iodine
• A thyroid ultrasound, which can look at nodules and gland size
• An electrocardiogram (ECG) if you have palpitations, to check your heart rhythm

Some medicines and supplements can affect test results. Biotin, a common ingredient in hair and nail supplements, is one example, so tell your clinician what you take before blood is drawn.

Treatment options for hyperthyroidism and Graves' disease

The choice depends on the cause, your age, other health conditions, whether you are pregnant or planning pregnancy, and whether you have eye disease. Your clinician, often an endocrinologist, will talk through the tradeoffs with you.

Medicines that lower hormone production

According to MedlinePlus, antithyroid drugs, mainly methimazole and propylthiouracil, reduce how much hormone the thyroid makes. They can bring levels down over weeks to months, and some people reach remission after a course of treatment, though outcomes vary and the condition can return. Both drugs can, uncommonly, lower white blood cell counts (agranulocytosis) or affect the liver. The prescribing label for propylthiouracil carries a boxed warning for serious liver injury, and clinicians often reserve that drug for particular situations, such as early pregnancy. Your care team chooses between the two drugs, so ask your prescriber or pharmacist about the cautions that apply to you.

Fever, sore throat or mouth sores while taking one of these drugs can be a sign of a dangerously low white blood cell count. Drug labels advise stopping the medicine and reporting these symptoms right away, and a blood count is usually needed the same day. Stop the antithyroid drug and call your prescriber right away. If you cannot reach them promptly, go to urgent care or the emergency room for a blood count rather than waiting for a callback. Yellow skin or eyes or dark urine can signal liver injury, so the same approach applies: stop the drug, call your prescriber, and get same-day liver testing through your prescriber, urgent care or the emergency room. Severe abdominal pain, repeated vomiting or confusion, especially with yellow skin, needs emergency care. In other situations, do not change your dose on your own; ask your prescriber.

Beta blockers for symptoms

Beta blockers can slow a racing pulse and ease shaking and anxiety while other treatment takes effect. They do not treat the thyroid itself. They are not appropriate for everyone, for example some people with asthma, so your clinician decides whether one fits you.

Radioactive iodine

Radioactive iodine is taken by mouth and gradually shrinks overactive thyroid tissue. Many people later develop an underactive thyroid and need daily thyroid hormone replacement. Our article on hypothyroidism explains that condition. Radioactive iodine is generally not used during pregnancy, and it can worsen eye disease in some people, so eye health is part of the decision.

Surgery

Removing all or part of the thyroid is another option, for example when the gland is very large, when nodules are a concern, or when other treatments are not suitable. A review of thyroid surgery for Graves' disease and Graves' ophthalmopathy in the National Institutes of Health PubMed Central archive discusses benefits and risks. Surgery carries risks such as effects on the nearby parathyroid glands and voice nerves, and most people need lifelong thyroid hormone afterward.

Pregnancy, older age and other situations that change the plan

If you are pregnant or could become pregnant, tell your clinician before starting or stopping any thyroid medicine. Uncontrolled hyperthyroidism in pregnancy is associated with complications for both parent and baby, and the choice of antithyroid drug is often different in early pregnancy because of safety concerns. Treatment is individualized, and decisions should come from your care team.

Older adults and people with existing heart disease deserve prompt attention, because a fast or irregular rhythm is more likely to cause trouble. If your racing heart wakes you at night, our article on waking up with a racing heart looks at other explanations, and our article on why the heart skips or flutters covers palpitations in general.

Thyroid storm: the rare emergency

Thyroid storm is a severe, life-threatening worsening of hyperthyroidism. It is much less common than ordinary hyperthyroidism, and having an overactive thyroid does not mean you will develop it. It can occur in people with a known overactive thyroid and, less often, as the first presentation of one. It can be set off by illness, infection, surgery, or missed treatment. Features can include a very fast heartbeat, high fever, agitation or confusion, vomiting or diarrhea, and extreme weakness. This needs emergency care and can progress quickly, so do not wait to see whether it improves at home.

What you can do while you wait for your appointment

• Write down your symptoms, when they began, and any weight change.
• Bring a full list of medicines and supplements, including biotin and any iodine-containing products such as kelp.
• Note your resting pulse if you have a way to check it, and any episodes of fluttering or dizziness.
• Limit caffeine and stimulants if they make palpitations worse, and mention it to your clinician.
• Tell your clinician about a family history of thyroid or autoimmune disease.

For an overview of thyroid conditions in general, see MedlinePlus on thyroid diseases.

When to Seek Medical Care