How long does it take to feel better on thyroid medication?

Reviewed by Chimene Richa, MD, 

Written by Andrea Pierce 

Reviewed by Chimene Richa, MD, 

Written by Andrea Pierce 

last updated: Oct 09, 2020

6 min read

What is the thyroid? 

The thyroid gland sits towards the bottom of the front of your neck, just under your voice box (larynx). It’s shaped like a butterfly, with a narrow stem and wide wings.

While small, your thyroid is a gland tasked with an essential function: making thyroid hormones. It uses iodine from your diet to make the hormone thyroxine—sometimes called T4. It also helps to make small amounts of triiodothyronine (T3), a thyroid hormone responsible for keeping your body energized and functioning as it should.   

Your bloodstream ships these hormones out to every corner of your body. Your thyroid gland plays a significant role in how you feel from day to day—energetic, sluggish, up, down, and more—by keeping the body supplied with thyroid hormones.

Among other things, these hormones affect:

  • Body metabolism

  • Energy levels

  • Normal functioning of your heart, brain, muscles, digestive system, and other vital systems

  • Body temperature

Given how important the thyroid gland is, you can see how thyroid disorders and abnormal levels of thyroid hormones can negatively impact your health.


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What can go wrong with the thyroid? 

Unfortunately, thyroid diseases are not uncommon. You can have an underactive thyroid (hypothyroidism), overactive thyroid (hyperthyroidism), or thyroid cancer. We will be focusing on hypothyroidism and hyperthyroidism in this article.


If your thyroid is underactive, it fails to produce enough thyroid hormone to keep the body running normally—this is called hypothyroidism. Many people of all ages and races, up to 5% of the general population, have hypothyroidism (Chiovato, 2019). People with hypothyroidism often have no symptoms or symptoms so mild that they don’t realize they have the condition—sometimes for months to years (NIDDK, 2016). 

Hypothyroidism can develop for several reasons, including autoimmune diseases (in which the body mistakenly targets itself) such as Hashimoto’s thyroiditis, radiation treatment, thyroid inflammation, medications, and surgical removal of the thyroid gland (NIDDK, 2016).  

Without enough thyroid hormone circulating in your body, you may feel low energy and generally wiped out.

Common symptoms of an underactive thyroid include (NIDDK, 2016):

  • Feeling cold most of the time and unable to warm up

  • Low mood, depression

  • Constipation—bowel movements slow down

  • Forgetfulness

  • Weight gain

  • Dry skin

  • Hair loss

  • Irregular menstrual cycles and/or fertility problems

  • Slow heart rate

  • Joint pain

There’s a wide range of how people experience hypothyroidism. Symptoms sometimes creep up so slowly over time, over months or even years, that people hardly notice that something’s wrong—they just think it’s how they are.

To make things more complicated, an underactive thyroid can also affect other health conditions. For example, hypothyroidism can contribute to high cholesterol levels, so people being evaluated for high cholesterol and heart disease may also need thyroid blood tests. 

Rarely, If the underactive thyroid is left untreated, you can develop a myxedema coma.  Myxedema coma is a rare, extreme form of hypothyroidism where the body’s functions slow to the point that it can be fatal (NIDDK, 2016). 


Just as the thyroid gland can become underactive, it can also become overactive—a condition called hyperthyroidism (“hyper” or high as opposed to “hypo” or low thyroid). Hyperthyroidism usually develops as an autoimmune disease. The immune system produces antibodies that stimulate the thyroid to make more thyroid hormone than it should (NIDDK-a, 2017). 

Another name for hyperthyroidism is Graves’ disease, and symptoms include fast heartbeat, fatigue, sleeplessness, nervousness, muscle weakness, increased appetite, diarrhea, weight loss, eye problems, and an uncomfortable shaky feeling (NIDDK-a, 2017).

Treatment for thyroid problems

The treatment for hyperthyroidism is to remove or inactivate the overactive thyroid. This can be accomplished with surgery, radioactive iodine, or antithyroid medications like methimazole or propylthiouracil (NIDDK-a, 2017).

Once you’ve removed or inactivated the thyroid gland, you no longer have a fully functional thyroid, and you become hypothyroid. There’s no cure for hypothyroidism, but for most people, they can effectively manage the condition—and feel better—with hormone replacement therapy using a man-made (synthetic) version of thyroid hormone.

Levothyroxine is the most common synthetic thyroid hormone used to treat an underactive thyroid, according to the American Association of Clinical Endocrinologists and the American Thyroid Association (Garber, 2013). Also sold under the brand names Synthroid, Levoxyl, and Tirosint, levothyroxine is a synthetic version of the T4 thyroid hormone. Your treatment of hypothyroidism entails restoring your thyroid hormone levels to normal.

In general, beware of over-the-counter thyroid “boosters,” which are often unreliable and lack scientific data to prove their effectiveness.

How long does it take to feel better on thyroid medication?

Since everyone’s physical makeup is a little different, and the reason for hypothyroidism can vary, finding the best formula for you will be a personal experience. It may take several weeks, as the peak effect of levothyroxine can take 4-6 weeks to achieve (DailyMed, 2019). How long it takes for you to feel better after starting a thyroid medication depends on things like dosage, timing, other medical conditions, your overall health, and more.

How does levothyroxine work?

Levothyroxine replaces the primary hormone produced by the thyroid gland that it can no longer make for itself. Be sure to carefully follow your healthcare provider’s instructions about when and how much to take every day. For example, you might be instructed to take the same dose daily or different amounts on different days of the week. 

Your healthcare provider will check your thyroid-stimulating hormone (TSH) levels with blood tests to see if your thyroid hormones are in balance; a high TSH means that you need more thyroid hormone and vice versa. 

You’ll likely have to take the thyroid hormone replacement for the rest of your life; once you stop, the symptoms of hypothyroidism will probably come back.


Your healthcare provider will estimate what dosage of thyroid replacement medicine to give you based on things like your age, weight, why you have low thyroid hormone levels and other factors. The dosage might also be influenced by other medicines you take—be sure to tell your provider about any other drugs you take, including prescriptions, over-the-counter medications, and dietary supplements. 

Levothyroxine is most effective if you take it on an empty stomach, 30-60 minutes before eating (DailyMed, 2019). Also, to maximize effectiveness, do not take calcium carbonate (like in over-the-counter antacids) or iron supplements, as they can prevent levothyroxine from being absorbed. Proton pump inhibitors like omeprazole (brand name Prilosec) and other antacids (brand names Maalox, Mylanta, etc.) may also decrease effectiveness because they reduce the absorption of levothyroxine. 

You may need to adjust your dosage over time. Often, healthcare providers start people on a low dose to get people used to the hormone replacement medicine and prevent symptoms of hyperthyroidism.

Be patient; it’s common to have to wait several weeks before starting to feel better. Thyroxine is slow-acting, and it can take time for levels of this hormone to rise to the target level. In a typical scenario, your healthcare provider will test your TSH level after 4-8 weeks to see how you have responded (Garber, 2013). In time, you’ll hit on the right dosage—and may continue with that for a very long time.

Side effects

Thyroid medication can cause a number of side effects, especially as you and your healthcare provider look for the right dosage for you. Most of the side effects of levothyroxine are similar to the symptoms of hyperthyroidism. They usually indicate that you are getting too much of the drug—in other words, too much thyroid hormone.

The U.S. Food and Drug Administration (FDA) has issued a Black box warning for levothyroxine (FDA, 2017): Do not use thyroid hormones, like levothyroxine, for weight loss or to treat obesity. Large doses of levothyroxine can lead to serious and life-threatening effects.

Common side effects of levothyroxine include (DailyMed, 2019):

  • Inability to tolerate high temperatures (heat intolerance)

  • Fever

  • Increased appetite

  • Weight loss

  • Tiredness

  • Hyperactivity

  • Excessive sweating (hyperhidrosis)

  • Nervousness/anxiety

  • Hair loss

  • Decreased bone mineral density

  • Muscle tremors

  • Diarrhea

  • Irregular menstrual cycles

  • Fertility problems

Serious side effects can occur, especially if the levothyroxine dose is too high. They mainly involve the heart and may include (DailyMed, 2019):

  • High blood pressure

  • Heart failure

  • Chest pain (angina)

  • Heart attack (myocardial infarction)

  • Fast heartbeat (tachycardia or palpitations)

  • Irregular heartbeat (arrhythmia)

  • Cardiac arrest (heart stops working)

If you experience any of these side effects, seek medical attention right away.

When to speak with your healthcare provider

If, after weeks of trying to establish the right thyroid medication dosage, you still just can’t shake that feeling of malaise—you’re depressed, dragging yourself through the day, or generally feel unwell—talk to your healthcare provider. If you become pregnant during treatment, be sure to tell your provider as thyroid hormones play an essential role in your baby’s development (NIDDK-b, 2017). Lastly, if you are experiencing any of the side effects mentioned, you should seek medical advice.

Your provider can check to make sure your TSH levels are normal and also evaluate you for signs of other medical conditions. Never stop taking your medications without guidance from your healthcare provider.


If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

How we reviewed this article

Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

Current version

October 09, 2020

Written by

Andrea Pierce

Fact checked by

Chimene Richa, MD

About the medical reviewer

Dr. Richa is a board-certified Ophthalmologist and medical writer for Ro.