Synthroid/Levothyroxine Complete Overview - History, Usage, Dosage, Interactions, Side Effects - Thyroid Advisor (2024)

Last Updated on February 19, 2022

History

The history of Synthroid, a medication for thyroid dysfunction in the form of levothyroxine sodium tablets, dates all the way back to the early 20th Century.

Thyroxine, levothyroxine at its purest form, was isolated by biochemist Edward Calvin Kendall at the Mayo Clinic in Rochester, Minnesota in 1914.

This experimentation first was conducted from the extracts of a hog’s thyroid glands. Then, in 1927, the hormone was created by two British chemists: George Barger and Charles Robert Harington.

Overtime, levothyroxine has been one of the most prescribed medications in the United States of America, when it comes to thyroid disorders.

Within the last 10 years, levothyroxine has become the 2nd most used prescription, with over 20 million filled prescriptions year-to-year.

Medical Use

Synthroid/levothyroxine has been used to cure hypothyroidism, or a low-functioning thyroid. Its goal is to add more thyroid hormones to the body. In turn, this should help the thyroid gland perform better – or how it normally should.

This substance needs to be used when the thyroid gland is either injured or showing lower hormone levels as normal thyroid hormones are important for physical and mental activity in our bodies, as well as fertility and preventing serious disorders such as thyroid cancer and/or goiters.

Dosage

Dosage for levothyroxine depends on a few factors. The official guide for dosage can be found on Synthroid’s website.

The first factor is based on age. If you are younger, then you will probably be getting a smaller dose compared to older people.

The second factor depends of weight. The more you weigh, the higher dosage you will receive for levothyroxine.

Also, depending on how low your thyroid hormone levels are will also directly affect your dosage amount. The last two factors that affect dosage are: your response to treatment and lab results. Depending on how you react to treatment, your doctor will lower or raise your dosage.

For example, if you are taking a low dosage of levothyroxine, but your body is showing no reaction to the medication, your doctor may raise the dosage, or visa versa, dependent on each situation.

Lab results may shine more light on how much levothyroxine you should actually be taking, based on blood tests, etc. Patients should be taking this medication regularly, without stopping. For consistency, take the medication at the same time every day for best results.

If you have concerns while taking levothyroxine, do not quit cold turkey all together. Talking to your doctor before making changes is always a smart choice.

How to Take

Levothyroxine or Synthroid is usually taken orally through a pill, without food. Your doctor will likely ask you to take levothyroxine one time per day with one hour before food (breakfast preferably).

You should drink an 8 ounce glass of water with the medication, unless your doctor has other thoughts for how you should take it.

Capsule form should be swallowed whole without chewing on the drug.

But, for children or people that can’t swallow, tablet form can be used as an alternative. With these tablets, break it and crush the substance and mix with water (approximately 1 to 2 teaspoons). The substance should never be mixed with soy formula, when giving to infants or children.

Always discuss these matters with a pharmacist or a doctor before breaking down this substance to a more finite being.

Dosages will also depend on the type of levothyroxine brands available for you to take.

Brands should never be changed without the approved consent of your doctor. If your doctor does not know of your intent to change brands, a different choice could have negative effects when paired with different medications.

How It Works

You may be wondering what causes an underachieving thyroid in the first place, and how levothyroxine works.

Well, the thyroid is responsible for producing two hormones: T3 (triiodothyronine) and T4 (levothyroxine).

The thyroid gland’s job is to create more T4 than T3 in the body, even though the T3 hormone is usually much more active than the T4 hormone. The cool thing about the human body is the fact that the T3 hormone can actually be changed to the T4 hormone if it is needed. You can learn more about the thyroid feedback loop here.

If the body does not naturally fix the problem, this is where medication can come into play.

Other options to help the thyroid gland along involves Armour Thyroid or other naturally desiccated thyroid prescription medications. These are medicines that contain actual thyroids and hormones extracted from pigs. There are some people who prefer this type of medication a lot more than Levothyroxine or Synthroid. Click here for a complete overview of Armour Thyroid vs Synthroid.

Even though levothyroxine is a synthetic drug, it still mimics the all-natural T4 hormone. In rare cases, a patient may need to take more T3 hormones in the form of Cytomel.

Interactions

There are a variety of brands to choose from when it comes to levothyroxine.

Make sure that you know the negative interactions if paired with other substances.

For example, specific medications like colestipol, iron, sodium polystyrene sulfonate, antacids, calcium supplements, and other substances can actually worsen the problem of an under-active thyroid, by lowering the hormones even more. If you are taking other prescriptions, make sure that you take them 4 hours apart from levothyroxine.

When drug interactions occur, this could lead to some horrible side effects or may change the entire make-up of the drug itself.

Your doctor should have a list of things you should not mix with levothyroxine like prescription drugs, herbal supplements, and/or non-prescription products.

Some products that may interactive negatively with levothyroxine include, but are not limited to, digoxin, blood thinners, and/or sucroferric oxyhydroxide.

Side Effects

Similar to a lot of prescription medications these days, there are a substantial number of side effects that may occur with levothyroxine if the drug is misused or the body does not react well with the substance.

If the body still continues to struggle with low hormone levels with the thyroid, even after taking levothyroxine, symptoms may present themselves such as aching muscles, weight gain, dry skin, a slower heartbeat, and tiredness, among other things. Your doctor should be notified if these symptoms persist. They will ultimately have the final say on judging if the side effects outweigh the benefits or not.

Other negative side effects may include hair loss with levothyroxine. Usually, this only happens as the body tries to adapt to the medication, but hair loss may continue overtime for a more prolonged issue.

These are times when the body does not adapt and serious health effects happen when the thyroid hormone levels are higher than normal. These symptoms are much more prevalent in the form of sweating, shaking, mood changes, and headaches. Medical attention needs to get involved if effects like chest pain, swelling, seizures, or an irregular heartbeat happens within the body.

In a rare situation, an allergic reaction can take place when using levothyroxine.

If this happens, you may notice symptoms such as itching, a rash, trouble breathing, and dizziness. Call a doctor immediately and report these negative effects to the Food and Drug Administration (FDA). Their phone number is 1-800-FDA-1088, and their website is www.fda.gov/medwatch.

Controversies

When it comes to Synthroid, the controversies come in the form of regulations and rules.

Synthroid, itself, has been used for the last 50+ years on the market to treat thyroid disorders. This should definitely be reassuring to hear for people being prescribed this medication, as generally Synthroid has had a positive profile, while being used by millions of people, young and old.

One of the controversies Synthroid has had, involves a task force which was created for adult hypothyroidism.

This group included members from the American Thyroid Association (ATA) and the American Association of Clinical Endocrinologists (AACE). They published a joint endeavor in 2012 entitled Clinical Practice Guidelines for Hypothyroidism in Adults.

This was created to help with diagnosis and treatment for hypothyroidism and pushed Synthroid as the treatment option.

The controversy began to present itself when members of the task force were linked to the company that made Synthroid. This gave off a bad vibe seeming the committee only wanted to write a report that would further their financial ties.

With their guidelines in place, the committee concluded three things should happen when dealing with hypothyroidism.

First, a Thyroid Stimulating Hormone, or TSH, is the screening test that should be used when dealing with dysfunction of the thyroid. Secondly, T4 treatment is the best replacement option. Lastly, treatment for hypothyroidism should be based on each patient. The first two guidelines resulted in controversy.

The first controversy came with TSH being the primary testing for thyroid dysfunction.

The TSH test has been accused of not being accurate when helping doctors’ diagnose a thyroid malfunction. For example, Richard Shames, a doctor based in California, has written a variety of books on the thyroid. He believes the samples taken for a TSH test are not accurate because samples are usually taken in the morning, while the blood is not ran through a machine until the evening.

This is ample time for the hormones to slow down even more, resulting in an under-active thyroid diagnosis from doctors. For best results, many experts recommend testing for TSH as well as free T3, free T4, reverse T3, anti-TPO antibody, antithyroglobulin antibody and SHBG.

The second controversy came from the guidelines saying that T4 hormones are the best replacement option when treating a thyroid disorder.

In fact, this recommendation has pushed doctors to not use T3 hormones to help with the problem. This ignores a variety of studies that have encouraged doctors to use T3 and T4 hormones in unison to help with the problem.

A 2009 study, that was published in the European Journal of Endocrinology, proved that using T3 and T4 hormones together in therapy against a thyroid disorder had better results than treatments that were only levothyroxine-based for some patients.

These results included less depression and anxiety within their patients. That is not to say that Synthroid is not a good option, but for some patients, other options as be better. At the same time, for some people Synthroid will be the best choice for their body.