Hyperthyroidism is a condition in which your thyroid gland produces more thyroid hormones than your body requires. It’s also known as “overactive thyroid.” It can harm the health of your heart, muscles, semen quality, and more if not treated effectively.

The small, butterfly-shaped thyroid gland is located in the neck. Hormones made by the thyroid gland affect your energy level and the functioning of most of your organs. Thyroid hormone, for example, plays a role in the beating of your heart.

The opposite of hyperthyroidism is the more common hypothyroidism, or “underactive thyroid,” which is when the gland doesn’t produce enough thyroid hormones to match the body’s needs.

While women are 2 to 10 times more likely than men to develop an overactive thyroid, male hyperthyroidism does occur and usually requires medications to keep it in check. Men and women share many of hyperthyroidism’s main symptoms, but there are some symptoms that are unique to men.

A condition known as Graves’ disease is the most common cause of hyperthyroidism for men, though women are still more likely to develop this autoimmune disorder.

Having Graves’ disease means your immune system mistakenly attacks a healthy thyroid gland, causing it to produce too much thyroid hormone. It usually develops between the ages of 30 and 50, though it can form at any age.

Other causes include:

  • nodules, which are abnormal clusters of thyroid cells within the gland
  • Plummer’s disease, also known as toxic nodular goiter, which is more common in women and people over age 60
  • thyroiditis, any of several conditions that cause inflammation of the thyroid gland
  • too much iodine intake from medicines or diet

There are many signs of hyperthyroidism. Some, like difficulty sleeping, you may not notice or think of as symptoms of a serious underlying health condition. Others, like an abnormally rapid heartbeat (even when at rest) should get your attention quickly.

Other common symptoms of hyperthyroidism include:

  • unexpected weight loss, even when food consumption and appetite remain unchanged
  • irregular heartbeat
  • heart palpitations
  • nervousness
  • irritability
  • fatigue
  • tremor (usually trembling of the fingers and hands)
  • sweating
  • increased sensitivity to heat and/or cold
  • more frequent bowel movements
  • muscle weakness
  • hair thinning

Though men and women tend to share most of the same common symptoms of hyperthyroidism, there are a few important complications that affect men only.

In particular, an overactive thyroid can contribute to erectile dysfunction (ED), as well as a low sperm count. Premature balding can also be a sign of hyperthyroidism in men.

Too much thyroid hormone can also cause lower levels of testosterone, which can lead to several complications. For example, men may also be more noticeably affected by a loss of muscle mass caused by hyperthyroidism.

Osteoporosis triggered by an overactive thyroid may also take men by surprise, as this bone-thinning disease is most often associated with women. A condition known as gynecomastia (male breast enlargement) can also be a result of hyperthyroidism.

Thyroid hormones affect the function of certain cells in your testes, according to a 2018 study in the . For example, too much or too little thyroid hormone can interfere with the healthy function of Leydig cells, which help produce and secrete testosterone.

Hyperthyroidism also affects sperm cells, leading to reduced sperm density and motility (how well sperm can move or “swim”). It can even affect the actual shape or form of the sperm themselves.

Thyroid disease is also associated with erectile dysfunction, though the connection still isn’t well understood. Both overactive and underactive thyroid disorders may affect erectile function, though hypothyroidism tends to be more commonly linked to ED.

All of this can lead to infertility. If you’ve been unable to father a child, a test of your semen quality may help lead to a solution. A low sperm count should be followed by a test of your thyroid hormone levels. These are simple tests that could lead to a treatment that will balance out your hormone levels, which in turn may help improve your sexual health, too.

Just because women may be more likely to develop hyperthyroidism, doesn’t mean that men shouldn’t be tested as their risks increase. You should have noticeable symptoms evaluated. You should also be screened for hyperthyroidism if you have a family history of thyroid disease or are over age 60. Likewise, you may be at higher risk if you have type 2 diabetes, in which case, you should consider thyroid disease screening.

Hyperthyroidism evaluation starts with a review of your medical history and symptoms. Your doctor may look to see if you have a tremor and changes in your eyes or skin. They may also check if you have overactive reflexes. All of these may indicate an overactive thyroid.

In addition to a physical exam, hyperthyroidism screening should include a test for thyroid stimulating hormone (TSH) and thyroxine, the main hormone released by the thyroid gland. An imaging test called a thyroid scan can also be helpful in diagnosing hyperthyroidism.

Talk with your doctor about getting screened, as thyroid disease is a widely underdiagnosed and undertreated health problem. An estimated 60 percent of people with some form of thyroid disease don’t know they have the condition.

Hyperthyroidism can be more difficult to treat than hypothyroidism, which can usually be managed by taking synthetic thyroid hormone. The options for overactive thyroid treatment include:

  • Antithyroid medications, such as methimazole, that cause the thyroid to make less hormone.
  • Surgery to remove all or part of the thyroid, which results in having to take synthetic hormone.
  • Radioiodine therapy, which involves taking radioactive iodine-131 by mouth. The iodine slowly kills some of the cells making thyroid hormone with the goal of bringing hormone production into a normal, healthy range. This is a widely used therapy that can sometimes require more than one treatment.

In addition to helping resolve symptoms related to heart rate, weight, energy, and other complications related to overactive thyroid, treatment of hyperthyroidism may also help resolve sexual dysfunction problems.

If you have symptoms of hyperthyroidism, don’t wait to be tested for this disorder. Damage to your health may be ongoing without you realizing it.

If you’re diagnosed with hyperthyroidism but don’t yet have any noticeable symptoms, still follow through with your doctor’s advice about treatment. Discuss all the risks and benefits of various treatment options before committing to one approach. The sooner you start to deal with hyperthyroidism, the less long-term harm it can cause.