Medically reviewed on Aug 17, 2022 by Jillian Foglesong Stabile, MD, FAAFP. 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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Thyroid issues like hyperthyroidism and hypothyroidism can impact your health in considerable ways—so many ways, in fact, that they can be difficult to diagnose. The lengthy list of symptoms leaves many diving down rabbit holes of health conditions only to be met with dead ends.
Can hyperthyroidism cause weight gain? We’re answering this question ahead. Plus, we’ll break down a handful of thyroid issues and how they impact metabolism, body weight, and overall health.
Hyperthyroidism, or an overactive thyroid, typically does not cause weight gain. If you’re experiencing weight gain due to thyroid dysfunction, this may be due to another thyroid condition known as hypothyroidism.
Hyperthyroidism is characterized by an overactive thyroid, or a thyroid gland that produces more thyroid hormone, known as thyroxine, than your body needs. This excess thyroxine throws metabolism off balance and often results in unexpected weight loss, anxiousness, or more frequent bowel movements. 
Hypothyroidism is just the opposite. It’s characterized by an underactive thyroid, or a thyroid gland that does not produce enough thyroxine for your body to maintain regular metabolic function. This often results in unexpected weight gain, fatigue, or constipation. 
To help identify whether you may be experiencing hyperthyroidism or hypothyroidism, you’ll need to know the difference in their warning signs and symptoms.
Someone with an overactive thyroid issue may experience these common symptoms: 
On the other hand, a person with an underactive thyroid condition may experience these symptoms: 
Whether you’re dealing with hyperthyroidism or hypothyroidism, both are likely to affect your weight. That’s because it all links back to the thyroid gland and the production of thyroid hormones and their role in metabolism.
The thyroid gland is a small organ in your neck that sends thyroid hormones across your entire body through your bloodstream. These hormones play a critical role in organ function, developmental growth, and metabolic regulation.
The primary thyroid hormones, T3 and T4, activate cells and kick them into high gear to process food, convert it into energy, and deliver that energy to vital organs like the brain and heart. 
The production of thyroid hormones is inextricably linked to our metabolism. Thyroid hormones regulate the rate at which your body converts food into energy. This process when the body is at rest is known as our Basal Metabolic Rate, or BMR. 
Thyroid hormone imbalances can negatively impact the BMR, or what’s considered a healthy metabolic rate. Here’s what that impact may look like:
The American Thyroid Association reports that the weight gain associated with an underactive thyroid issue is usually insignificant, adding only 5 or 10 pounds to a person’s regular weight.  That said, the amount of weight gained usually depends on the severity of the hypothyroidism itself.
Screening for hypothyroidism can be accomplished by:
Your thyroid undoubtedly plays an instrumental role in your overall health. Whether you’re gaining unexpected weight, experiencing symptoms of hyperthyroidism or hypothyroidism, or you’d just like to be more proactive about your health, the Everlywell Thyroid Test can unlock key information to know.
Our at-home test uses a simple finger prick sample collection and delivers detailed, personalized information about your unique thyroid health—all from your couch.
The Everlywell Thyroid Test goes further than just measuring TSH. It covers TSH, Free T3, Free T4, and thyroid antibodies to give you a holistic view of your thyroid health. Receive results straight to your phone and hold the power of proactive health in your hands.
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Hypothyroidism vs. hyperthyroidism: the key differences explained
23 possible symptoms of an overactive thyroid