Medically reviewed on July 14, 2023 by Jordan Stachel, M.S., RDN, CPT. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.
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The thyroid, a small, butterfly-shaped hormone gland located in the neck, plays a vital role in metabolism, as well as the growth and development of the body.  It’s fibrous and comprises several lobules that store thyroid hormones including, triiodothyronine, tetraiodothyronine, and calcitonin. 
That said, when the thyroid dysfunctions, these hormones are disrupted. This can lead to several thyroid disorders that can cause many symptoms such as fatigue, weight gain, and dry skin. 
Fortunately, thyroid medication is available to help rebalance the hormones. Although medications may have side effects, including weight loss and/or weight gain, the effects will typically differ from person to person.
Common Thyroid Conditions
One of the primary functions of the thyroid gland is to regulate metabolism. More specifically, the thyroid hormones control the rate at which cells convert food into energy, thereby influencing the body's overall energy expenditure. They help determine how quickly the body uses oxygen and nutrients, and play a vital role in maintaining a healthy body weight. 
The thyroid gland is also essential for :
- The regulation of internal body temperature
- Bone growth
- Brain development
- Cardiovascular functioning
- Reproductive health
As such, thyroid issues can impact the whole body and can result in various conditions such as:
- Hypothyroidism – This condition occurs when the thyroid gland is underactive and does not produce enough thyroid hormones. Symptoms may include fatigue, weight gain, cold intolerance, constipation, depression, and dry skin, as well as joint and muscle pain and a slowed heart rate. Hypothyroidism can also contribute to high cholesterol and, if left untreated, may be life-threatening. 
- Hyperthyroidism – Hyperthyroidism is characterized by an overactive thyroid that produces an excessive amount of thyroid hormones. Symptoms may include weight loss, increased appetite, heat intolerance, irritability, anxiety, rapid heartbeat, and trembling hands. Have you ever wondered about the link between your thyroid and period changes? This type of condition may also impact the menstrual cycle and cause fertility issues. Often, hyperthyroidism is caused by Graves’ disease, with four out of five cases resulting from this type of thyroid disease. 
- Graves' disease – This autoimmune disorder causes the overproduction of thyroid hormones, leading to hyperthyroidism. Essentially, the immune systems of people with this disease attack the thyroid, causing it to make more hormones. Symptoms may include goiter (an enlarged thyroid gland), bulging eyes (exophthalmos), weight loss, anxiety, and insomnia. Similar to hyperthyroidism, Graves’ disease can also affect the menstrual cycle and fertility. 
- Hashimoto's thyroiditis – Like Graves’ disease, Hashimoto’s thyroiditis is an autoimmune disorder in which the immune system attacks the thyroid gland, leading to chronic inflammation and, unlike Graves’ disease, reduced thyroid function. Consequently, Hashimoto's thyroiditis is a common cause of hypothyroidism. Symptoms can include tiredness, muscle weakness, excessive weight gain, depression, cold intolerance, and changes to the skin and hair. 
- Thyroid nodules – Thyroid nodules are abnormal growths or lumps in the thyroid gland. They can be benign (noncancerous) or malignant (cancerous). Most thyroid nodules are benign and do not cause symptoms. However, large nodules or those that produce excess thyroid hormones, can lead to hyperthyroidism. Research has found that approximately 20% to 76% of adults have thyroid nodules, which are not typically cancerous. 
- Thyroid cancer – Thyroid cancer develops when abnormal, malignant cells in the thyroid gland grow uncontrollably. As a result, the thyroid can enlarge and create a visible lump in the neck. Patients with thyroid cancer may find it difficult to swallow or breathe. They may also experience hoarseness, enlarged lymph nodes, and pain when swallowing. 
- Thyroiditis – Thyroiditis refers to inflammation of the thyroid gland. This can be caused by various factors, including viral or bacterial infections, autoimmune conditions, or changes that occur to the thyroid postpartum. Depending on the type of thyroiditis, it can cause temporary hyperthyroidism or hypothyroidism. 
Thyroid Medications and Their Side Effects
Depending on your condition, there are several thyroid medications that can help to rebalance your hormones in the case of thyroid dysfunction. But does thyroid medication cause weight loss? Ultimately, it depends on the type of medication and its use case.
Those with an underactive thyroid (hypothyroidism) are most often given one of the following medications :
- Levothyroxine (Synthroid, Levothroid, Levoxyl, Unithroid)
- Liothyronine (Cytomel)
- Liotrix (Thyrolar)
- Natural thyroid (Armour Thyroid, Nature-throid, Westhroid)
For these medications, specifically, weight loss may occur if hormonal balances initially caused weight gain. As hormone levels and the metabolism return to normal, people taking these types of medication may return to a more normal, healthy weight.
Conversely, patients with an overactive thyroid (hyperthyroidism) are often prescribed :
- Propylthiouracil (PTU)
- Methimazole (Tapazole)
Side effects can include skin rashes, an upset stomach, and drowsiness. In extreme cases, those taking medication for hyperthyroidism may experience a sore throat, fever, chills, jaundice, and liver disease. Additionally, since hyperthyroidism can often cause weight loss in those affected, this condition's treatment may result in weight gain. 
See related: Does Thyroid Medication Affect Your Menstrual Cycle?
Stay on Top of Your Thyroid Health
If your thyroid condition initially caused weight gain, such as the case with hypothyroidism, it’s more likely that treatment will cause weight loss. That said, weight loss is not always a side effect of thyroid treatment and many thyroid medications can lead to weight gain, depending on the root cause and what is needed to achieve hormonal homeostasis.
To understand thyroid levels and check your hormone levels at home, partner with Everlywell. Our at-home Thyroid Test can easily measure your thyroid hormones and TPO antibodies so that you can better understand your thyroid function and use this understanding to take steps toward better health. Or, if you want to meet with a healthcare professional, check out our online thyroid telehealth services. Through this telehealth offering, Everylywell will connect you with a licensed clinician who can answer your questions and provide you with recommendations.
Jumpstart your journey today with Everlywell.
Does Thyroid Medication Affect the Menstrual Cycle?
What Causes Thyroid Eye Disease?
Can a Woman With Thyroid Problems Get Pregnant?
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