The thyroid is a small, butterfly-shaped gland in the neck that carries an outsized amount of responsibility. As part of the endocrine system, it produces hormones that regulate metabolism the complex process by which the body converts food into usable energy. When it works properly, most people never think about it. When it does not, the effects can ripple through nearly every system in the body.
There are two main ways the thyroid can malfunction: it can become underactive, a condition called hypothyroidism, in which it does not produce enough hormone, or it can become overactive, known as hyperthyroidism, in which it produces far too much. Both can produce symptoms that are easy to dismiss or attribute to something else entirely, which is part of why thyroid disorders are so frequently missed.
The most reliable way to diagnose either condition is through a blood test that measures TSH (thyrotropin) levels. An elevated TSH typically indicates an underactive thyroid, while a very low TSH points to an overactive one. The encouraging news is that once a diagnosis is made and treatment begins, many symptoms can be reversed.
Below, endocrinologists walk through 20 signs that your thyroid may be off and what each one might mean.
Signs of an underactive thyroid (hypothyroidism)
Unexplained weight gain — gaining five to 10 pounds without any meaningful change in diet or exercise habits can be a hallmark of hypothyroidism. The weight tends to present as a specific type of fluid retention rather than fat accumulation.
Extreme fatigue — this is the most commonly reported symptom of hypothyroidism. It goes well beyond ordinary tiredness; no amount of sleep relieves it, and even after a full night of rest, the exhaustion persists.
Changes in hair and eyebrows — the hair can become dry, brittle and prone to breakage or shedding. In rare cases, a person may also notice thinning or loss of the outer portion of the eyebrows.
Constipation — a slower metabolism affects digestion too. When the colon is not contracting as it should, or the body is absorbing too much water from food, stool moves too slowly and chronic constipation can follow.
Heavier or longer periods — thyroid disease is well established as a disruptor of the menstrual cycle. With hypothyroidism, periods may come more frequently, last longer, be heavier and involve more cramping than usual.
Puffiness or bloating — fluid retention can make the face appear puffy, and a slowed digestive system including slower stomach emptying can cause persistent bloating, particularly after eating.
Brain fog and memory problems — difficulty concentrating and short term memory issues are commonly reported in hypothyroidism. Research suggests that the condition may alter brain pathways involved in cognition, particularly those connected to the hippocampus.
Unexplained aches and pains — joint pain and tingling that seem to come out of nowhere, without any physical exertion to explain them, are a frequently overlooked symptom of an underactive thyroid.
Constant cold sensitivity — feeling perpetually cold, even in warm environments, is tied to the body burning less energy and therefore producing less heat. Even hands and feet may remain stubbornly cold.
Depression and low mood — there is a documented link between hypothyroidism and both anxiety and depression. Research published in the Nordic Journal of Psychiatry found associations between thyroid dysfunction and depressive symptoms that can significantly affect daily functioning.
Signs of an overactive thyroid (hyperthyroidism)
Intolerance to heat — when thyroid hormones are running in excess, the body’s ability to regulate temperature is compromised. A person may feel persistently hot and sweaty, even in cool environments.
Unexplained weight loss — losing weight without any change in diet or activity level or even while eating more than usual can signal hyperthyroidism. The weight loss can range from barely noticeable to as much as 20 pounds in more severe cases.
Frequent bowel movements — excess thyroid hormone speeds up the body’s processes, including digestion. An increased metabolic rate and faster gut movement can result in more frequent bowel movements or even diarrhea.
Hand tremors — overstimulated nerves are a hallmark of hyperthyroidism. A fine trembling in the hands is one of the more noticeable neurological effects of excess thyroid hormone.
Lighter or absent periods — in contrast to hypothyroidism, an overactive thyroid can cause periods to become lighter, shorter and more spaced out or to stop entirely, which may contribute to fertility difficulties.
Difficulty sleeping — the surge of thyroid hormone keeps the body in a near constant state of stimulation, making it hard to fall asleep or stay asleep. Hot flashes and digestive discomfort can compound the problem.
Anxiety and irritability — mood changes are common when the body is in overdrive. Anxiety and irritability can be amplified further when poor sleep is also in the picture, creating a difficult cycle to break.
Vision disturbances — blurred, dry or irritated eyes are a frequent complaint among people with hyperthyroidism. In more severe cases, particularly in a condition called Graves’ disease, the eyes can visibly protrude a condition known as proptosis.
Heart palpitations or irregular heartbeat — excess thyroid hormone can cause the heart to race even while at rest. In some cases, this leads to atrial fibrillation, an irregular and potentially serious heart rhythm that carries risks of heart failure and blood clots. It affects an estimated 5 to 15% of hyperthyroidism patients, with older individuals at greater risk.
Muscle weakness — difficulty lifting objects or completing routine physical tasks like climbing stairs can be a sign that hyperthyroidism is affecting muscle function, even in people who were previously active without any difficulty.
