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Can You Smoke While Taking Levothyroxine?

Learn how and why a smoking habit may impact your thyroid health in this article.
Can You Smoke While Taking Levothyroxine?
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No organ system in your body benefits from cigarettes, the thyroid included. Most people think of the heart and lungs as most affected by cigarette smoke, but the thyroid can be just as damaged. Smoking not only worsens symptoms of hypothyroidism (underactive thyroid), but it can also increase a person's risk for thyroid disorders like Graves' disease. It can also prevent thyroid medications from doing what they need to do to keep your thyroid hormone levels healthy.


Smoking and thyroid function


The thyroid gland is a small, butterfly-shaped gland at the base of the neck that makes hormones that control the body's metabolic functions. Ahead, how smoking impacts your thyroid function.



The toxins inhaled from cigarette smoke (including second-hand smoke) interfere with thyroid functions. Tobacco contains cyanide, which converts to thiocyanate when inhaled into the body. Thiocyanate has three primary effects on your thyroid gland:


  • It prevents the absorption of iodine into the thyroid. Iodine is necessary for producing T4 and T3 in the thyroid. When iodine is not available in sufficient quantities, it can inhibit the thyroid's ability to make thyroid hormones.
  • It interferes with the synthesis of thyroid hormone within the thyroid gland. 
  • It forces the kidneys to excrete more iodine, leading to thyroid-specific issues like inflammation and systemic concerns like fever and nausea. 


People who have hypothyroidism will be further compromised by smoking, as their already decreased T4 and T3 levels will become even lower. Thus, smoking worsens your hypothyroid symptoms like fatigue, depression, muscle slowness, and weight gain. 



Nicotine is the primary ingredient that causes addiction to tobacco products. Intriguingly, nicotine has the opposite effect on the thyroid gland. Nicotine has been shown to activate thyroid function and may even inhibit the actions of thiocyanate in the thyroid gland. However, the presence of nicotine does not equally outweigh the harmful effects of thiocyanate. 


Cigarettes contain other harmful substances as well, including carbon monoxide and tar. Each of these ingredients plays a role in causing damage to all organs in the body, including the heart, vascular system, digestive system, reproductive system, bones and muscles, and the immune system. 


Autoimmune thyroiditis and cigarettes


Two primary autoimmune disorders can affect the thyroid: Hashimoto's disease and Graves' disease


Hashimoto's Disease

Hashimoto's is a condition where the immune system attacks the thyroid gland, making it unable to produce enough thyroid hormones. This disease is the leading cause of hypothyroidism in the United States. Unfortunately, there is little research about how smoking affects Hashimoto's. However, it is not uncommon for people with the disease who smoke to develop goiters, especially when they are iodine-deficient.



Smoking may increase the risk of a goiter regardless of the number of cigarettes smoked. Research suggests that the association between smoking and developing a goiter is primarily seen in younger women and older adults. Again, the risk of smoking-induced goiter is believed to be highest in populations with an iodine deficiency. 


Graves' Disease

Graves' disease is also the result of an overactive immune system, where antibodies mimic the hormones usually released by the pituitary gland to signal the thyroid to make more hormones. Thus, people with Graves' disease have an overactive thyroid gland. 


For reasons unknown, Graves' disease is twice as common in people who smoke compared to non-smokers. One of the hallmark signs of Graves' disease is a goiter, which is an enlargement of the thyroid gland. People with Graves' who smoke generally respond poorly to treatment and struggle with worse symptoms than non-smokers.  


At the root of these autoimmune thyroid diseases is underlying chronic inflammation. When the body is exposed to toxins, especially repeatedly, it quickens the progression of the disease and makes symptoms much more difficult to bear.


How smoking interferes with levothyroxine


We know the impact of smoking on thyroid function and the production of thyroid hormones, which is problematic for people with hypothyroidism. The first line of thyroid treatment for hypothyroidism is thyroid medication. Levothyroxine, a synthetic form of thyroid hormone, is one of the most popular thyroid hormone replacement medications. People who start smoking while taking levothyroxine may need to increase their dose to make up for the interference caused by smoking. 


However, some studies suggest that taking levothyroxine may reduce the severity of withdrawal symptoms when people decide to quit smoking. Furthermore, it is important to monitor your thyroid levels carefully with thyroid blood tests, as you may not need as much levothyroxine once you stop smoking. 

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Steps to quit smoking


Smoking is harmful to your health and can shorten your life span, and second-hand smoke can also cause health problems in those around you. Choosing to stop smoking will help ward off any further damage to your body. However, the path to cessation is not smooth and requires a plan and purpose to help you work through the difficulties ahead.


Talk to your doctor

When you decide to quit smoking, it can help to talk to your doctor, who may prescribe medications that will curb your cravings. Additionally, your healthcare provider can prepare you for any medication and health changes you will need to prepare for, such as setting up periodic blood tests to check your thyroid function. 


Gather your support network

Let your friends and family in on your plans so they can help cheer you on. Suppose someone in your inner circle currently smokes. In that case, it may be challenging to interact with them while you are withdrawing, so it can help to be upfront with them about your intentions. 


You can find support outside of your family and friends as well. Indeed, it is usually helpful to align yourself with other people going through the same process. Look for social support groups or sign up for apps that offer services to help you stay strong on your road to smoking cessation.


Create your Quit Plan

Your Quit Plan is made entirely by you and serves as a road map to help you achieve your goal. Visit to create a personalized Quit Plan. 


Additional Resources for Smoking Cessation


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