Smoking and Thyroid Disease: What Changes When You Quit

Thyroid problems and cigarettes interact in ways that surprise many people. If you have Graves’ disease, you may have been told that smoking puts your eyes at risk. If you have recently quit, you may have read that stopping can trigger an underactive thyroid and wondered whether that is a reason to worry. The relationship between smoking and thyroid health cuts both ways, and the details matter. This guide explains what the evidence says about smoking, Graves’ disease and thyroid eye disease, what happens to thyroid function after you quit, and when a thyroid blood test makes sense.

How Smoking Affects the Thyroid

The thyroid is a small, butterfly-shaped gland in your neck that makes hormones controlling how your body uses energy. Most common thyroid diseases are autoimmune, meaning the immune system attacks the gland. Graves’ disease makes the thyroid overactive, while Hashimoto’s disease, the main cause of an underactive thyroid in the UK according to the NHS, slows it down.

Smoking pushes these two conditions in opposite directions. A review in Clinical Endocrinology summarized the evidence (Wiersinga, 2013):

• Smoking is a dose-dependent risk factor for Graves’ hyperthyroidism, and especially for Graves’ eye disease.
• Smokers with Graves’ have a higher chance of the overactivity coming back after treatment.
• Current smoking is linked to a lower risk of thyroid antibodies and autoimmune hypothyroidism, but that effect disappears within about three years of quitting.
• In iodine-deficient areas, smokers are more likely to have an enlarged thyroid (goiter) and nodules.

The British Thyroid Foundation explains that chemicals in smoke can stimulate the immune system to react against the thyroid. Smoking also reduces oxygen in tissues, and low oxygen makes the tissue behind the eye more prone to inflammation. This fits the wider picture of how cigarettes disrupt immunity, covered in our article on smoking and the immune system. Thyroid disease is not the only immune-related condition where this matters, as our guide to smoking and Crohn’s disease shows.

Graves’ Disease and Thyroid Eye Disease in Smokers

Thyroid eye disease (TED), also called Graves’ orbitopathy, is an autoimmune condition in which the muscles, eyelids and fatty tissue around the eye become inflamed. The British Thyroid Foundation’s thyroid eye disease leaflet (revised 2024) describes red, swollen, uncomfortable eyes, eyes pushed forward, and sometimes double vision. Rarely, it can threaten sight.

The leaflet estimates that about 40% of people with Graves’ disease develop TED at some point. In most cases it is mild, and only 5% to 6% develop moderate to severe disease. Smoking changes those odds substantially:

The American Thyroid Association lists exposure to cigarette smoke, including secondhand smoke, as a factor that makes TED more likely to develop or get worse. It advises people with TED who smoke to try to quit and to avoid secondhand smoke too.

Smoking can also affect treatment of the thyroid itself. The British Thyroid Foundation says non-smokers and ex-smokers are more likely to be cured of an overactive thyroid after a course of the antithyroid drugs carbimazole or propylthiouracil than people who smoke. It also advises caution with radioactive iodine in active TED, especially in smokers.

This short scenario from the British and Irish Orthoptic Society shows how eye clinicians can support a smoker with thyroid eye disease to think about quitting.

Does Quitting Help Thyroid Eye Disease?

Yes, and the benefit appears to start early. The British Thyroid Foundation says the risk of TED seems to decline very rapidly after quitting. It also notes that people with TED who keep smoking respond less well to treatment, but that this disadvantage seems to disappear soon after giving up.

Quitting is not a treatment on its own, and TED needs care from both an eye specialist and a thyroid specialist. But smoking is a risk factor you can change. The British Thyroid Foundation lists smoking reduction, alongside keeping thyroid levels steady and avoiding radioactive iodine in active TED, as a core way to prevent TED from worsening.

What about vaping? The foundation says there is no research yet on vaping and TED, and that the safest option for your eyes and general health is to stop both. On nicotine replacement therapy (NRT), it says TED experts consider NRT as appropriate for smokers with TED as for anyone else.

Smoking harms the eyes in other ways too. Our guide to eye health after quitting covers cataracts, macular degeneration and more.

Hypothyroidism After Quitting: What the Studies Found

This is the part of the story that can sound alarming out of context. Because smoking seems to suppress the autoimmune process behind Hashimoto’s disease, stopping can remove that suppression for a while.

The clearest data come from Denmark. Researchers monitored thyroid tests across two regions and identified 140 people newly diagnosed with overt autoimmune hypothyroidism, comparing them with 560 matched people with normal thyroid function (Carlé et al., Clinical Endocrinology, 2012).

A Dutch study of women with a family history of autoimmune thyroid disease found a similar signal: stopping smoking was associated with a higher chance of developing thyroid antibodies (Effraimidis et al., Journal of Clinical Endocrinology and Metabolism, 2009).

Three points keep this in proportion:

• It is temporary. In the Danish data, the extra risk was concentrated in the first two years and was not seen after three years.
• It is a relative risk. The study needed more than 2 million person-years of observation to find 140 cases, so most people who quit will never develop it.
• It is treatable. The NHS says an underactive thyroid is usually treated with levothyroxine tablets and people can live a normal life.

The Danish authors were explicit: stopping smoking is vital to prevent death and severe disease. Their advice was not to keep smoking but for doctors to stay alert to hypothyroidism in people who have recently quit.

Withdrawal or Your Thyroid? Overlapping Symptoms

Nicotine withdrawal and thyroid problems share several symptoms, which can make the first months after quitting confusing. The NHS says withdrawal can cause irritability, restlessness, difficulty concentrating, trouble sleeping and low mood, usually easing over three to four weeks.

Symptom lists are from the NHS pages on underactive thyroid, overactive thyroid and nicotine withdrawal. The key difference is time. Withdrawal usually peaks in the first week and fades over weeks, while the NHS notes that underactive thyroid symptoms usually develop slowly and get worse over time.

Keeping a simple record helps. iQuit’s mood and craving journal lets you log energy and mood day by day, which gives your GP a clearer picture than memory alone.

Weight Changes: Thyroid, Metabolism or Appetite?

Most people who quit gain some weight, and it is easy to blame the thyroid. In a BMJ meta-analysis, people who quit without treatment gained an average of 2.85 kg by three months and 4.67 kg by 12 months, with wide variation (Aubin et al., BMJ, 2012). The NHS explains that nicotine suppresses appetite, so appetite often increases after you quit.

Our breakdown of metabolism after quitting explains what actually changes, and our guide to quitting without gaining weight has practical strategies.

Weight gain that keeps climbing beyond the usual pattern, especially alongside tiredness, feeling cold and constipation, is worth checking. So is unexpected weight loss with a racing heart or trembling, which can point to an overactive thyroid.

When to Ask for a Thyroid Test

A thyroid function test is a simple blood test that measures thyroid-stimulating hormone (TSH) and thyroxine (T4). The NHS says to see a GP if you think you might have an underactive thyroid. Given the Danish findings, it is reasonable to mention that you have recently quit smoking.

Consider asking about a test if:

• Tiredness, low mood or poor concentration are still getting worse more than a month or two after quitting, rather than easing
• You notice several signs of an underactive thyroid, such as feeling cold, constipation, dry skin or a hoarse voice
• You have signs of an overactive thyroid, such as palpitations, trembling, heat intolerance or weight loss
• You have a personal or family history of thyroid or autoimmune disease
• You have Graves’ disease and notice eye changes such as grittiness, redness, bulging or double vision; tell your doctor promptly

If you already take thyroid medicine or other regular medicines, tell your doctor or pharmacist that you are quitting. Some medicines need monitoring when smoking stops; see our guide to medication dose changes.

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