What’s the Difference Between Hypothyroidism and Hyperthyroidism?

Imagine a tiny butterfly-shaped gland in your neck that has the power to speed you up or slow you down. This little powerhouse is your thyroid, a key player in managing how your body uses energy. But what happens when this gland doesn’t work as it should?

For some, their thyroid hits the brakes, causing a sluggish state known as hypothyroidism. For others, it hits the gas pedal, leading to overdrive known as hyperthyroidism. While both conditions are linked to the thyroid, they’re quite different in how they affect your body and how they’re treated.

“Your thyroid gland affects pretty much every part of your body,” explains endocrinologist Mary Vouyiouklis Kellis, MD. “The hormones it secretes regulate your metabolism and your ability to tolerate heat or cold. They can also change your energy levels, mood and menstrual cycles.”

Dr. Vouyiouklis Kellis helps make sense of the differences between an overactive and underactive thyroid.

Hypothyroidism vs. hyperthyroidism

Hypothyroidism and hyperthyroidism are both conditions related to your thyroid gland and the hormones it secretes. When those hormones become imbalanced, it can lead to a thyroid disorder.

Here are some of the main differences between these two disorders:

• In hypothyroidism, you don’t produce enough thyroid hormone. This slows some bodily functions down. You can feel fatigued, depressed and hypersensitive to cold. You may gain weight and develop constipation.
• In hyperthyroidism, you have too much thyroid hormone. This revs some things up. You may feel anxious, experience insomnia and get hot, sweaty and flushed. You can lose weight without meaning to and develop heart palpitations.

Both conditions come with even more symptoms, which we’ll break down next.

Symptoms of hypothyroidism vs. hyperthyroidism

It’s no surprise that some of the signs of hypothyroidism are related to feeling slower and more tired. But it can affect more than just your energy levels. Symptoms of hypothyroidism include:

• Fatigue
• Weight gain or difficulty losing weight
• Feeling cold easily
• Dry skin and hair
• Hair loss
• Muscle weakness
• Joint pain or stiffness
• Depression or mood changes
• Trouble concentrating or memory problems
• Slow heart rate
• Constipation

On the flip side, hyperthyroidism might raise your body temperature, speed up your heartbeat and even make you a little jittery. Symptoms of hyperthyroidism include:

• Feeling anxious, nervous or irritable
• Weight loss
• Feeling hot or sweating a lot
• Rapid or irregular heartbeat
• Tremors (shaking hands or fingers)
• Difficulty sleeping
• Increased appetite
• Muscle weakness
• Diarrhea or more frequent bowel movements
• Bulging eyes (in some cases)

While most symptoms are quite different, there are a few that can overlap, such as:

• Fatigue. Both conditions can cause tiredness, though with hyperthyroidism, it’s often linked to trouble sleeping or feeling restless.
• Muscle weakness. With both hypothyroidism and hyperthyroidism, you can experience muscle weakness, though the reasons are different.
• Mood changes. Both conditions can lead to mood changes, like feeling down with hypothyroidism or anxious with hyperthyroidism.
• Abnormal or irregular periods. In some cases, an overproduction or underproduction of the thyroid hormone can affect your menstrual cycle.

Causes of hypothyroidism vs. hyperthyroidism

While both conditions are related to problems with your thyroid, the overall causes vary.

Some of the causes of hypothyroidism include:

• Hashimoto’s disease. This is the most common cause. In this condition, your body’s immune system mistakenly attacks your thyroid gland, making it less able to produce thyroid hormones. This, in turn, damages your thyroid and prevents it from making enough of the hormone.
• Thyroid surgery. If you’ve had surgery to remove part or all of your thyroid (for example, because of cancer), you might not have enough thyroid left to make hormones.
• Radiation treatment. Treatments for certain cancers can affect your thyroid and lower hormone production.
• Iodine deficiency. Your thyroid needs iodine (a mineral) to make hormones. If you don’t get enough iodine in your diet, it can lead to hypothyroidism. This is rare in places where salt is iodized.
• Medications. Some medicines, such as those used to treat heart conditions or psychiatric disorders, can affect your thyroid function.

Some of the causes of hyperthyroidism include:

• Grave’s disease. This is the most common cause of hyperthyroidism. Here, your immune system starts to overproduce an antibody, which damages your thyroid. But this time, it results in your thyroid producing too much hormone.
• Thyroid nodules. Sometimes, lumps or nodules can form on your thyroid, and these can produce extra hormones.
• Thyroiditis. This is when your thyroid becomes inflamed and leaks too much hormone into your bloodstream. This can happen after a viral infection or as part of an autoimmune condition.
• Too much iodine. While a lack of iodine can cause hypothyroidism, too much iodine (from diet or certain medicines) can cause hyperthyroidism.

Treating hypothyroidism vs. hyperthyroidism

As you may have guessed, an overactive thyroid is treated differently from an underactive thyroid. While hypothyroidism requires treatment that replaces missing hormones, hyperthyroidism involves treatments that reduce your hormone production to bring it back to a more balanced state.

Treatments for hypothyroidism include:

• Thyroid hormone replacement. The most common treatment is taking a daily pill that contains synthetic (man-made) thyroid hormone, usually called levothyroxine. This pill helps replace the missing hormone and brings your hormone levels back to normal.
• Regular blood tests. Once you start taking thyroid hormone replacement, you’ll need regular blood tests to make sure the dose is correct. Your doctor will adjust the dose if needed.

In addition, your healthcare provider may recommend a change in diet to help manage your symptoms. 

Treatments for hyperthyroidism include:

• Antithyroid medications. These pills help slow down your thyroid and reduce the amount of hormone it makes. Common antithyroid medicines include methimazole and propylthiouracil (PTU).
• Radioactive iodine therapy. This treatment uses a special type of iodine that damages thyroid cells so they stop making too much hormone. The iodine is swallowed as a pill, and it only affects your thyroid gland.
• Beta-blockers. This medication doesn’t fix the thyroid itself, but it can help manage symptoms like a fast heartbeat and shaking. Beta-blockers are often used along with other treatments.
• Thyroid surgery. Sometimes, part or all of your thyroid gland may need to be removed. This usually is necessary if you haven’t responded well to other treatments, have large thyroid nodules or have a thyroid that’s very overactive. After surgery, you might need to take thyroid hormone replacement if not enough of your thyroid is left.

Is one worse than the other?

While hypothyroidism is more common than hyperthyroidism, Dr. Vouyiouklis Kellis notes that neither of them is necessarily worse. Either way, it’s best when your hormones are balanced. So, whether your thyroid is producing too much or not enough, it can cause problems.

Typically, hypothyroidism develops more slowly and is sometimes considered easier to treat (usually through taking a pill for hormone replacement, as opposed to surgery). But this will vary based on your health history and what kind of treatments you respond best to.

The bottom line

You’ll live your best life when your thyroid is functioning well. If you’re experiencing any of thyroid-related symptoms — or if you’re just not feeling like yourself — talk to a healthcare provider.

Dr. Vouyiouklis Kellis stresses that it’s also important to share with your provider any family history of thyroid conditions, which will put you at much higher risk for developing a thyroid problem.

Your provider will run lab tests to find out whether you might have hypothyroidism, hyperthyroidism or another condition that can be addressed so you can feel your best.