What is Synthroid&Reg;?

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  • Originally Written By: Karyn Maier
  • Revised By: C. Mitchell
  • Edited By: Jay Garcia
  • Last Modified Date: 07 November 2019
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Synthroid® is a commercially produced synthetic version of the human thyroid hormone thyroxine. People who for whatever reason aren’t able to produce adequate levels of thyroxine for themselves often depend on this chemical supplement or a similar competing brand to stay healthy. The drug itself is branded and proprietary, but the core chemicals that form its base are used in a number of different pharmaceutical drugs and are sold under several different brand names in markets around the world. In most places this drug has been a standard treatment for hypothyroidism, the medical term for low levels of thyroid hormone, since the 1950s.

Why the Hormone Matters

Thyroxine is generally understood to be essential to good health, which is one of the reasons it’s so important to synthetically supplement people who don’t make enough on their own. The primary function of this hormone is to regulate the metabolic rate of the cells found in virtually every tissue in the human body. It is also responsible for regulating body temperature and plays a role in cognitive functioning and in the digestion of food. For people with low thyroid hormone levels, these processes become impaired, which can lead to hypothyroidism. Hypothyroidism is usually a chronic condition. It doesn’t go away on its own, and it often gets worse with time.


Synthetic hormones can also be a problem for people who produce too much thyroxine, a condition known as hyperthyroidism. To some degree it may seem counterintuitive to add a synthetic version of a hormone that a person is already producing in excess, but it can work in certain limited scenarios. One of the biggest benefits of the synthetic compound is that it can suppress thyroid hormone release in the right therapeutic dose. As a result, it’s sometimes used to inhibit the growth of thyroid nodules and goiters, and the therapy is also sometimes combined with anti-thyroid medications such as methimazole to achieve more controlled results.

Role in Pharmaceutical Development

The generic name for Synthroid® is levothyroxine sodium, but it is also sold under the brand names Levoxyl®, Levothroid®, and Unithroid® in many places. Most forms of levothyroxine are available in tablet form. However, this medication is sometimes prescribed in powdered form to be mixed with liquid and delivered by intravenous injection. Since there may be differences in concentration between brands, the dosage may need to be adjusted to achieve effectiveness or to avoid toxicity.

Importance of Regular Monitoring

Most people who begin synthetic thyroid hormone therapy can expect to stay on the medication for the rest of their lives. However, adjustments may be needed adjusted periodically since life changes can affect its efficacy. In women, for instance, pregnancy and menopause are two factors that can impact thyroid metabolism. Complications may also arise as thyroid levels are normalized if other conditions are present; people with heart conditions taking beta-blocking drugs or insulin for diabetes may need to have the dosages of these medications adjusted while on the drug, and any major changes in health should be documented and discussed periodically with the prescribing doctor.

Most physicians want to monitor their thyroid patients at regular intervals to be sure the medication is still working the way it should. Patients taking Synthroid® typically have their thyroxine levels checked periodically through a Thyroid-Stimulating Hormone (TSH) test. Unless conditions indicate otherwise, this test is usually administered twice a year.

Side Effects and Common Interactions

While the compound is generally well tolerated in most people, there are a few documented side effects. Common symptoms include profuse sweating, rapid heart rate or pulse, headache, fever, insomnia, nausea, and unexpected weight loss. In addition, some women may experience irregular menstrual cycles.

Synthroid® may also interact with other medications. For instance, it is known that this drug can increase the action of certain blood thinning medications, which can lead to dangerous conditions. In addition, patients who are being treated with epinephrine for coronary artery disease may have an increased risk of suffering a heart attack while on the thyroid medication. Anyone who is concerned about the risks and benefits of this or any other medication is usually encouraged to talk to their healthcare provider.


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Post 2

If someone has a family member prone to thyroid issues (especially women), it's important to have a complete thyroid panel done, not just the TSH. The T-1 and T-3 levels need to be checked, also. The TSH doesn't tell the doctor everything.

Even when taking synthroid, a person should have a complete thyroid panel done once a year or so.

Post 1

I had the right lobe of my thyroid removed due to a nodule, and have been on synthroid ever since. It took a while to get my dosage correct. It's better to sneak up on the correct levels, rather than prescribe too much, which can cause all sorts of nasty side effects.

Personally, I've tolerated the synthroid pretty well. I don't have any noticeable side effects, and I certainly feel better now that my thyroid levels have normalized.

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