Liothyronine (T3) is the most potent thyroid hormone that you can take.
It is rarely prescribed by most doctors, which is unfortunate, because it can significantly improve your hypothyroid symptoms and overall quality of life.
The symptom improvements can include improved energy, weight loss, and even a reduction in depression.
Learn who could benefit from using liothyronine, how to use it safely, and lots more in this article...
In order to understand liothyronine, it is important that you understand the basic physiology of the thyroid. You can read more in depth about it by clicking here.
Liothyronine is T3. T3 is one of the 2 main circulating thyroid hormones in your bloodstream.
T4 is the inactive thyroid hormone. The vast majority of hormone made by the thyroid gland is T4.
T4 itself has no activity in the body. In order for it to become an active hormone, it must be converted into T3. An iodine molecule is cleaved off of the T4 by an enzyme called a deiodinase, which results in the production of T3.
T4 can be looked at as the storage reservoir for thyroid hormone in your body. When your body needs more active thyroid hormone, it can convert the T4 that is circulating in the blood into active T3.
By understanding that T4 is the inactive form of thyroid and T3 is the active form, it then makes sense why oral T3 medication is much more potent than oral T4 medication. In fact, it is about 3-4 times more potent.
If Liothyronine is so powerful, then why don't more doctors prescribe it?
Most doctors simply were not taught how to prescribe T3 medication and manage patients that are taking it. They were also not taught which labs need to be monitored and how to interpret those test results.
I was personally NEVER taught about T3 medications in my many years of training. I have had to learn about it myself through attending multiple medical conferences, reading tons of literature, and asking doctors with experience prescribing it how they use it.
It is simply assumed by most doctors that all patients have no issues with converting T4 to T3. If that was the case, every patient could just take a T4 only medication such as Synthroid, levothyroxine, or Tyrosint and it would seamlessly be converted to T3 when the body needed it.
Wouldn't that be easy?
However, most people with thyroid issues have a reduced ability to convert T4 to T3. Instead, much of the T4 is converted into the anti-thyroid metabolite reverse T3 which results in a condition called reverse T3 dominance. This is usually due to chronic inflammation in the body and/or a deficiency of nutrients such as iodine, selenium, or zinc.
That is why you may be on a good dose of a T4 only medication which results in a normal TSH and T4 level, yet you still have symptoms of hypothyroidism.
In those situations, when used and monitored properly, liothyronine can be a safe and extremely effective medication to treat your hypothyroidism and improve your symptoms.
One study showed that replacing T4 with T3 resulted in weight loss and greater thyroid action on lipid metabolism, without an increase in side effects.
Not everyone who takes thyroid medication necessarily needs to take liothyronine.
Besides having hypothyroidism, if you are otherwise healthy, energetic, and feel great, your conversion of T4 to T3 is probably adequate and you may not need to change from your T4 only medication.
Now, for the other 99% of you (ha!), you may want to get a complete thyroid panel so that you can truly assess the T4 and T3 levels in your body:
You should also consider getting a sex hormone binding globulin level (SHBG), which can also help give you an idea of the thyroid levels in your body (if you are on oral birth control pills or estrogen or if you smoke, this test will not be helpful).
If your reverse T3 level is >15, your free T3 level is <3.5, and/or your SHBG level is <20 in men or <60 in women (who aren't taking oral estrogen), then your T3 level is inadequate and you may want to consider adding T3 in some form to your regimen.
Below is a general list of people who may need to add T3 to their thyroid medication regimen:
This is by no means an exhaustive list, but it includes the majority of patients that may benefit from taking T3.
If you are currently taking a T4 only medication (Synthroid, levothyroxine, or Tyrosint), changing to an NDT medication such as Armour Thyroid, NP Thyroid, or Nature-throid may be the easiest thing to try to increase your T3 level. In fact, that is usually the first thing I will do for patients.
NDT is about 80% T4 and 20% T3. While that is certainly better than a medication with 100% T4, that may still be too much T4 which could result in a high level of reverse T3.
If you are taking an NDT medication and your reverse T3 levels are too high and your free T3 levels are too low, you may need to reduce your NDT dose (at least temporarily) and add a small dose of liothyronine in order to "flush out" the reverse T3 which will allow the T3 levels to rise to optimal levels.
Liothyronine may cause weight loss but it should NOT be used as a weight loss medication.
If used for weight loss in patients without thyroid dysfunction, it could cause some unpleasant and even dangerous side effects.
However, liothyronine may help with weight loss in patients with hypothyroidism.
T3 may cause more weight loss than T4 because of how it interacts with fat cells and other hormones in the body.
T3 directly increases mitochondrial energy production and increases thermogenesis and fat burning potential.
Liothyronine can also reduce symptoms of depression.
Low thyroid levels (hypothyroidism) are known to commonly result in symptoms of depression.
What you may not know is that adding liothyronine to an antidepressant can improve mood and cognitive function even when the thyroid function is normal.
The exact mechanism is not fully understood, but it is believed that some patients with depression may have subclinical hypothyroidism that is not bad enough to be detected on standard lab tests but still causes typical symptoms of depression.
Therefore, by treating those patients with liothyronine, it may correct those subtle thyroid abnormalities in the brain which will help resolve the depression symptoms.
T3 has also be shown to increase the receptor sensitivity to serotonin and increase the synaptic concentrations of serotonin.
Since the most commonly used antidepressants are only successful in treating depression in about 50% of cases, the addition of liothyronine is a viable option to consider, especially in "treatment resistant" cases.
If you are on a T4 only thyroid medication and are still suffering from depression, adding liothyroinine to your T4 medication may significantly improve mood and neuropsychological function.
The whole point of even discussing liothyronine is because we want to raise the active thyroid levels (T3) in the body to optimal levels.
Taking T3 medication (liothyronine) will obviously accomplish that goal. There are also some natural things that should be considered that will result in increased levels of T3. Let's discuss those as well as how to take liothyronine...
The conversion of T4 to T3 is dependent on a few nutrients.
It is common for people to be deficient in these nutrients because they may be lacking in their diet or they may have gut issues such as leaky gut that reduce the absorption of the nutrients.
Some of the most important nutrients include:
Another way that you can raise T3 levels and improve its function is to lower reverse T3 levels.
Remember, reverse T3 is the anti-thyroid metabolite that binds to thyroid receptors on the cells but blocks their function.
By reducing the amount of reverse T3, it will in effect improve T3 function.
So how do you do it? Address the issue that is causing the reverse T3 level to be increased in the first place.
Easier said than done, but below is a list of common issues that result in elevated reverse T3 levels:
Cytomel is the brand name for liothyronine, but over the past few years generic versions have become available that are less expensive.
Liothyronine is available in 3 strengths - 5mcg, 25mcg, and 50mcg. I personally have never prescribed the 50mcg dose.
Typically, the 5mcg dose is prescribed first, then it may be increased to 10mcg (2 tablets) depending on the patient response and labs. If more is needed, usually 1/2 pill of 25mcg is given, then possibly a full 25mcg tablet.
This is by far the most common way that liothyronine is used. Fortunately, medical providers are becoming more comfortable using it so its use is expanding.
Liothyronine is added to the patient's current dose of T4 medication (levothyroxine).
Remember, liothyronine is 3-4 times more potent than levothyroxine, so you will need to be aware of any side effects and your labs will need to be monitored closely.
If your TSH is suppressed excessively, it may be necessary to reduce your dose of levothyroxine.
Most physicians will not be comfortable prescribing liothyronine by itself.
This is because most medical committees recommend using a T4 thyroid medication as first-line treatment of thyroid issues.
However, many patients with weight loss resistance, leptin resistance, and other hormone imbalances may benefit from using T3 by itself.
T3 medication can be used temporarily to boost the body back into action or it can also be used long-term.
As long as it is used correctly and monitored closely there should not be any long-term consequences in using it.
If you are interested in using it, you must find a doctor with experience in prescribing it, and you must be willing to get regular lab tests and follow-ups with your doctor.
Occasionally patients may be extremely sensitive to T3 medication. In those situations, it may be necessary to have a compounding pharmacy make a sustained-release form of T3.
The sustained-release formulation will allow the T3 to be released gradually over a longer period of time which will reduce the side effects that the T3 may cause.
Some patients tend to be very sensitive to T3 medication. This usually causes them to feel jittery or anxious when they start the medication.
If you have a history of being sensitive to other medications, you need to let your doctor know before starting T3. You can probably still take it, but you will need to go "low and slow" with it.
As a general rule, I have found that women tend to be more sensitive to T3 than men, although there are certainly exceptions with both.
The side effects of liothyronine seem to mirror those caused by hyperthyroidism. These include:
If you develop any of these symptoms you should notify your prescribing doctor and discuss treatment options.
Liothyronine is a T3 only medication.
It is the most potent thyroid medication available.
When used correctly and closely monitored, liothyronine is extremely effective in treating hypothyroidism and reducing symptoms. It typically causes some weight loss as well.
It can also be used to treat resistant depression.
Now it's your turn...
Have you ever taken liothyronine? If so, what were the results?
Leave any questions or comments below.
Dr. Whelchel is a family physician who specializes in functional medicine, especially hormone optimization. He has over 20 years experience in private practice managing patients with various medical issues. His passion is helping patients reach their full potential of wellness and quality of life. He grew up in the Texas Panhandle where he currently lives. He is married and has 3 awesome children.