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Cynomel Vs Cytomel-[Detailed Comparison]

It is amazing how an organ can affect so much in your body. Starting from temperature to your body’s use of energy, thyroid glands help your functions work smoothly. And if something went wrong with the thyroid gland can lead you to hypothyroidism. 

To treat hypothyroidism we have different kinds of medication to get us back on the track. Among them two of the most popular medications are Cynomel and Cytomel. Their names may indicate similarity but they are obviously different. 

So, if facing the choice of cynomel vs cytomel then what to choose and why? 

Cytomel is made by Pfizer in the US and Cynomel is made by Sanofi in France. Both are brands of T3 medications but Cytomel is stronger when compared to Cynomel which is weaker. Difference between Cytomel and Cynomel is not in the amount of hormone presence in the tablet. But rather how they absorb in the body. 

Before diving deeper into them let’s see what hypothyroidism is.

Table of Content

Hypothyroidism Vs Hyperthyroidism

Hypothyroidism is simply a health condition that may affect pretty much everything in your body. Starting from your heartbeat to your weight, body temperature and even your body’s use of energy. It happens when the level of your thyroid hormones becomes low. 


Thyroid hormones are basically just messengers produced by your thyroid glands. Thyroid glands are found just below your Adam’s apple. After production of thyroid hormones your thyroid glands send these messengers to different parts of the body. 

These hormones travel to different parts of your body regulating all types of functions and processes. 

The analogy of a car would be suitable here. You can control all the functions through the pedal. If you want to decrease or increase the speed, just balance your foot on the pedal. 

Similarly, thyroid hormones if balanced keep all processes in your body running smoothly. Whether it’s your body temperature, heartbeat or your metabolism , all controlled by these hormones. 

For whatever reason if your thyroid gland produces low thyroid hormones, it is called hypothyroidism. Similarly if thyroid hormones are produced too much it is hyperthyroidism. 

Let us first see the difference between Cytomel and Cynomel at a glance.

Cynomel VS Cytomel-[Major Difference]

Cytomel is Us product by Pfizer.Cynomel is made in France by Sanofi.
People allergic to thyroid hormones extracted from beef or pork use Cynomel 
Cytomel is mostly extracted naturally from animals we feed onCynomel is prepared synthetically from iodine or thyroglobulin as well. 

Now moving towards how thyroid hormones are prepared.


Thyroid Hormones Preparation

Thyroid hormones are either prepared naturally which means extracted from animals we feed on. Or instead prepared synthetically. 

Thyroid Hormones Natural Preparation

Natural preparation of thyroid hormones include two things.

  • Desiccated Thyroid
  • Thyroglobulin

Desiccated thyroid is derived from the animals that humans use for food. And thyroglobulin is extracted from the thyroid gland of a hog. 

Thyroid Hormones Synthetic Preparation

Iodine content of natural preparation is standardized by USP United States Pharmacopeia. Natural preparation of thyroid hormones contains the following.

  • Iodine (At Least NLT 0.17% and Max 0.23 MNT%)
  • Thyroglobulin (At least 0.7% of organically bound iodine)


Cytomel are used to treat symptoms of following health conditions.

  • Low Thyroid Hormones (Hypothyroidism)
  • Enlarged Thyroid Gland (Non toxic goiter)
  • Myxedema
  • Myxedema coma

Cytomel belongs to the class of thyroid products and is used alone as well as with other medications.

How is Cytomel Made?

Thyroid hormone products are either natural or synthetically prepared. Synthetic preparation either contains Tetraiodothyronine sodium (T4, levothyroxine) or triiodothyronine sodium (T3, liothyronine). Furthermore, they may contain both.

T4 and T3 both are produced in thyroid glands by iodination and coupling of amino acid tyrosine. And Both are stored as thyroglobulin in the thyroid colloid. 

Cytomel Dosage

Dosage of thyroid hormones (Cytomel) are different from person to person based on patient response. Cytomel tablets are given orally and one dosage per day is recommended. Furthermore recommended starting dosage for mild hypothyroidism is 25mcg daily. 

Although based on patients response daily dosage may be increased upto 25mcg by 1st week. 

For myxedema starting dosage is 5 mcg daily. Which can be increased to 10 mcg by a week or two. And for congenital hypothyroidism the starting dose is 5mcg daily. For the desired response to be achieved an increment is 5 mcg every three to four days. 

In addition to that, for non toxic goiter dosage starts from 5 mcg. And based on patients’ response it can go upto 10 mcg every week or two.


Thyroid hormone drugs are used as supplemental therapy in patients with hypothyroidism of any cause. These drugs are not used in Transient hypothyroidism (During recovery phase of subacute thyroiditis). And this category includes the following.

  • Cretinism.
  • Myxedema.
  • Ordinary Hypothyroidism of any age.
  • Pediatric patients, adults and elderly.
  • Pregnancy.
  • Atrophy.
  • Absence of thyroid gland (Partial or Total).
  • Effects of radiation, drugs or surgery.

Cytomel Drug Interactions

Initially thyroid replacement therapy may cause insulin increase or may require oral hypoglycemic. Furthermore, thyroid hormone may increase the metabolism of vitamin-K. So, patients on oral anticoagulants should be watched closely when initiating thyroid replacement therapy. 

Cytomel Side Effects

The most common side effect of Cynomel is nausea and others are the following.

  • Headache
  • Irritability
  • Trouble sleeping
  • Heat Intolerance
  • Diarrhea
  • Menstrual changes in women

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Cynomel (liothyronine, T3) is used for the treatment of myxedema coma or precoma. Patients who are allergic to desiccated thyroid or thyroid extracted from beef or pork, use Cynomel. 

In addition to that, cynomel is used to treat the following.

  • Hypothyroidism
  • Euthyroid goiter
  • Hyperthyroidism
  • Myxedema
  • Cretinism
  • Thyroid Aplasia
  • Thyroiditis
  • After thyroid gland surgery

Remember that cynomel is a natural thyroid hormone activity supplement.

Cynomel Dosage

First of all remember that Cynomel ( liothyronine sodium) is only for intravenous administration. And it should never be injected as intramuscularly or subcutaneously. Initially the patient’s status and response to therapy should be continuously monitored on dosage of cynomel.

Emergency treatment of myxedema coma requires Cynomel dose ranging from 20mcg to 50mcg. However for cardiovascular patients the initial suggested dose is 10mcg to 20mcg. For therapeutic assessment 4 hour are allowed between doses.

However, to avoid fluctuation of hormone levels dosage time should not exceed more than 12 hours. Furthermore, for myxedematous patients dosage should start at low level and gradually increase. Because myxedematous patients are sensitive to thyroid hormones. 

Cynomel Drug Interactions

There are no established studies for safety and effectiveness of cytomel in pediatric patients. Patients should first receive adrenocortical hormone therapy before starting Cynomel. Similarly primary myxedema patients also require adrenocortical hormone replacement therapy before Cynomel.

Cynomel Side Effects

Cynomel most frequent adverse side effects are given below.

  • Arrhythmia
  • Tachycardia
  • Cardiopulmonary Arrest
  • Hypotension
  • Myocardial Infarction
  • Angina
  • Congestive heart failure 
  • Fever
  • Hypertension
  • Phlebitis
  • Twitching 
  • Allergic skin reaction


Thyroid hormone activity drugs are used for the treatment of obesity. However, in euthyroid patients small dosage is ineffective for weight loss. And larger doses may pose serious life threatening toxicity. 

Thyroid hormones should be given.to follow with great cautions.

  • Patients with angina pectoris
  • Elderly with occult cardiac disease
  • Insipidus or adrenal cortical insufficiency patients.

Final Verdict

Both Cynomel and Cytomel are thyroid hormone products. One is made in France by Sanofi and the other by US Pfizer. 

The major difference between them is how they are prepared. Cytomel is prepared from animals and Cynomel is also natural but syhthetically as well.


What are the strongest thyroid medications?

Levothyroxine is the strongest thyroid medication available. Not to mention levothyroxine is approved by the FDA. Because of the vast amount of available data about its use, levothyroxine is widely prescribed for thyroid replacement. The most known and widely used brands of levothyroxine are Synthroid, Levo T and Levoxyl.

Why is Levothyroxine not available in the market?

Levothyroxine is taken off the market due to FDA drug safety recall warning. Because this medication doesn’t contain the amount of levothyroxine that is needed. Furthermore, use of these medications can lead to symptoms of hypothyroidism including fatigue, constipation, hair loss and depression. In addition to that, inaccurate potency and stability data analysis certificates were found. And due to substandard practice that can lead to inconsistent levels of the active ingredients. 

Does magnesium interfere with Cytomel?

Yes, magnesium does interfere with Cytomel. So take your thyroid medicines at least 4 hours before magnesium containing medications. Furthermore, medicines containing aluminum, iron, calcium, simethicone or sucralfate also interfere with Cytomel. So medication with these ingredients should be taken with a gap of at least 4 hours. 


Now you know the cynomel vs cytomel difference. And you know that both are pretty same except the cytomel is stronger. Furthermore these are prepared by different companies.

In addition to that, people allergic to desiccated thyroid extract from beef or pork should avoid Cytomel. Instead they should use the synthetic version of Cynomel.

Furthermore, never ever use these prescription medicines with the recommendation of a certified physician. These are drugs that if used carelessly may cause life threatening toxicities. 

Be aware, stay safe. That’s all.

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