Symptoms of overactive thyroid, or hyperthyroidism, include double vision, bulging eyes, hair loss, heart arrhythmia, goiter, muscle weakness and rapid heartbeat, states WebMD. These symptoms are often unclear and can also resemble those of other conditions or illnesses.
Goiter happens to most people with overactive thyroid, and it shows up in the form of a lump at the front of the neck, according to WebMD. However, in some cases, only a doctor can find the goiter, as it may still be quite small. People who believe they have a hyperthyroid should undergo a blood test looking for thyroid-stimulating hormone, known as TSH. The pituitary gland releases this hormone to tell the thyroid to create thyroid hormone. Other blood tests look at thyroid hormone levels and the thyroid-stimulating antibody. Abnormal test results may spur the doctor to order a thyroid scan, radioactive iodine uptake test or thyroid ultrasound.
In addition to the symptoms listed above, weight loss combined with increased appetite, rapid fingernail growth, thinning skin, lighter menstrual bleeding, less frequent menstrual periods and loose bowel movements that occur frequently can also be a sign of overactive thyroid, explains WebMD. People with some or all of these symptoms should consult with a doctor.