Synthroid is a well-known brand of T4-only aka levothyroxine sodium, and has been around for a long time. This article is to explain this brand. I talk a lot about T4 in general in the updated revision STTM book. Janie Bowthorpe, site creator and hypothyroid/Hashi’s patient.

What is Synthroid?

Synthroid is a brand name of the thyroid storage hormone T4 and made by Abbott Laboratories in the US and Mylan in Canada. It’s been around for decades. It’s the most well-known brand name for what’s called levothyroxine sodium, a synthetic, man-made version of the thyroid hormone T4.

Technically, it’s a synthetic, man-made crystalline L-3,3′,5,5′-tetraiodothyronine sodium salt. Doctors have been prescribing Synthroid for over 50 years to treat hypothyroidism. Before that time, the only treatment for hypothyroidism was natural desiccated thyroid, which appeared to work well for a good seven decades before Synthroid entered the arena due to a single bad batch of NDT which came into the United States. See more details in the updated revision STTM book.

Inactive ingredients include acacia, confectioners sugar (contains corn starch), lactose monohydrate, magnesium stearate, povidone, and talc. These fillers may be different in other brands of T4-only. The Synthroid sizes ranges from 25 mcg all the way to 300 mcg.

What is T4?

T4 is one of five hormones made by your thyroid gland– the latter which includes T4, T3, T2, T1 and calcitonin. T4 is a storage pro-hormone with the purpose of converting to the active hormone T3, though the thyroid also makes some direct T3 as well. T3 is the hormone which gives health and energy to every cell in the body. See Chapter 1 in the revised STTM book for more info on these thyroid hormones.

What are other brands similar to Synthroid for T4-only?

Levoxyl, Levothroid, Unithroid, Berlthyrox, Eltibio, Eltroxin, Eutroxsig, Oroxine, Droxine, Eferox, Elthyrone, Euthyrox, Eutirox, generic levothyroxine, and more. They can have different fillers.

What’s the history of Synthroid or T4-only medications?

This is covered in Chapter One of the revised Stop the Thyroid Madness book with interesting detail and is interesting and a must read.

Is Synthroid an adequate treatment for hypothyroidism all by itself? Does Synthroid work all by itself?

The answer is varied according to the reported experiences of patients.

1. For some, yes, it does provide some relief of some hypothyroid symptoms due to conversion to T3, the life-changing active thyroid hormone.

2. For others, patients report that it fails from the beginning, leaving unresolved problems unique to each individual, resulting in continuing and worsening hypothyroid symptoms the longer one stays on it.

3. But for what appears to be certain percentage, there are reports of growing or worsening symptoms of an inadequate treatment the longer nothing but T4 is used, whether Synthroid or other T4 brands.

i.e a body of hypothyroid patients report continuing hypothyroid symptoms in their own degree and kind, sooner or later, which can include lingering fatigue, the need to nap, poor stamina or strength, depression, rising cholesterol or blood pressure, dry skin or hair, digestive problems, easy weight gain, difficulty losing weight, a diagnosis of Chronic Fatigue Syndrome or Fibromyalgia, brain fog, anemia, low B12, adrenal issues and many more.

Browse this compiled, patient-reported list of lingering or worsening symptoms while on nothing but T4-only meds of a variety of brands, and which only went away when they switched to having T3 in their treatment, whether adding T3 to that T4, or being on a working desiccated thyroid.

Why do hypothyroid patients on Synthroid (or other T4-only brands) see rising symptoms the longer they stay on?

T4 is a storage hormone meant to convert to the active and life-changing T3. It’s T3 which removes symptoms. But there are a myriad of issues which can hinder the conversion of T4 to T3, or causing conversion to RT3. They range from one’s genetic mutations, illnesses, chronic stress, too much exercise, poor eating habits, lyme disease, viral infections, low iron, inflammation, high cortisol from stress, mold exposure… to even your body aging.

Is there an issue with Synthroid (or other T4-only brands) being “synthetic”?

Honestly, no. It still works if you combine it with T3, say a growing body of patients. 

In a particular STTM blog post written by Janie Bowthorpe in 2012, she refers to an article with an interesting viewpoint, stating that synthetic T4-only medications like Synthroid are “unfortunately a mix of the left handed, nature-made combination of molecules, aka L-(Laevorotary), along with the synthetic, man-made right handed version, aka D-(Dextrorotary), i.e. the latter is a mirror-image, not a direct image.” As a result, one ends up with a lot of waste products, states the author of the article, and not the true T4.  But Janie presents it as food for thought. It still works well with T3 in one’s treatment.

Where can more information about the problem of using nothing but T4-only meds be found?

The T4-only Meds Don’t Work page gives a good outline of why these medications may not be working well for a certain body of hypothyroid or Hashimoto’s patients and why.

Chapter One in the UPDATED revised Stop the Thyroid Madness book also contains more details of the patient-reported problem of being on nothing but-only medications–a must have book and considered the Bible of Thyroid Treatment.

If a patient doesn’t want to be on Synthroid or other T4-only meds, what’s another choice?

Patients have been reporting getting getting far better results by adding T3 to their treatment, such as adding a brand of T3 to T4. They also work to achieve optimal with it so that the good results don’t backfire. If one can find a working desiccated thyroid, that also works well, too.  See this.

My doctor refuses to prescribe anything other than T4. What do I do??

Important note: STTM is an information-only site based on what many patients worldwide have reported in their treatment and wisdom over the years. This is not to be taken as personal medical advice, nor to replace a relationship with your doctor. By reading this information-only website, you take full responsibility for what you choose to do with this website's information or outcomes. See the Disclaimer and Terms of Use.