Your thyroid gland produces two key hormones: T4 and T3. About 80 percent of the hormone produced is T4, the remainder is T3. T4 is a storage hormone, and needs to be converted in the body into T3. T3 is the active thyroid hormone. T3’s job is to facilitate the frontline delivery of oxygen and energy to your cells, tissues, glands, and organs.

Conventional medicine assumes that your body is capable of converting T4 into T3 at sufficient levels, so synthetic T4 — levothyroxine — is the best treatment. According to endocrinologist Antonio Bianco, M.D., Ph.D., the medical community believes that “'Hypothyroid patients should be given only T4, as opposed to both T3 and T4. Then the body, in its wisdom, will make enough T3."

At least 15 percent of people in the United States treated for hypothyroidism still have unresolved symptoms. When you don’t have enough T3 reaching your cells, you are functionally hypothyroid. The signs and symptoms can include fatigue, weight gain, depression, concentration and memory problems, hair loss, joint and muscle aches, dry skin, constipation, infertility, elevated cholesterol, erratic menstrual periods, and other signs of slow-downs in your key bodily functions.

More than a dozen research studies have evaluated the benefits of adding T3 to T4-only treatment for hypothyroidism. Most of the studies found benefits to T4/T3 combination therapy, including improved mood, and better energy and concentration. Some studies also showed reductions in cholesterol and body weight. Two studies that have been especially influential include a 2011 study published in the Journal of Clinical Endocrinology and Metabolism, and a 2014 study published in Best Practices in Research: Clinical Endocrinology and Metabolism.

One important study from Denmark was published in the European Journal of Endocrinology. In the study, the majority of patients on T4/T3 combination therapy reported better quality of life, mental health, and energy; and reduced depression and anxiety. A total of 49 percent of the patients preferred the combination treatment. Only 15 percent preferred levothyroxine alone.

Genetic defects called deiodinase polymorphisms make some people less able to convert T4 into T3. These patients may require T4/T3 combination therapy to resolve symptoms. Dr. Bianco’s Bianco Lab at Chicago’s Rush University studies the issue. Says Dr. Bianco: "Hypothyroid patients are not all the same. Some will do better on the combination therapy; others not. The challenge is to identify these individuals and understand why these differences exist.”

If you have signs and symptoms of insufficient T3, a key step is to have blood tests to measure your T3 level. The preferred test is free triiodothyronine or free T3. This measures the available, unbound amount of T3 circulating in your bloodstream. (The total T3 test measures all the T3, including the bound and unavailable T3.)

At most labs, the reference range for free T3 is 2.3 to 4.2 pg/mL. Some physicians consider an optimal free T3 level for symptom relief to be in the upper half of the reference range, or from 3.3 to 4.2 pg/mL.

There are several ways your physician can add T3:

• Adding synthetic T3 such as brand-name Cytomel or generic liothyronine to levothyroxine
• Adding compounded, prescription, time-released T3 to levothyroxine
• Adding a natural desiccated thyroid (NDT) drug such as Nature-throid, Thyroid WP, Armour Thyroid, or generic to levothyroxine. NDT contains natural T3.
• Stopping levothyroxine entirely, and switching you to an NDT drug

It can take weeks to feel the effects of added T3, but some people feel them right away.

Thyroid patient Leah felt immediate effects: "Within 20 minutes of taking my first dose of generic Cytomel, I was like a wilted flower put in water. On T3 I have my life back. I can hold down a full-time job; I have enough energy to keep up with my grandchildren."

Some patients find it easier to lose weight when taking T3.

On levothyroxine, Jessica was 40 pounds heavier, fatigued and frustrated: "Within three months of taking Armour, it increased my weight loss, and I felt better. I'm happy with this medication!"

After years of not feeling well, Kristin pushed her endocrinologist for Cytomel: "I finally started feeling like me, and able to diet and lose weight. I feel the best I ever have and have lost over 30 pounds with dieting, and it's stayed off!"

Kathy was on Armour for several years: "Although better than Synthroid, I was still very tired. I added Cytomel six months ago and am 100 percent better. "

Lesley's numbers we're all in the normal range but she felt tired all of the time: " My endocrinologist prescribed Cytomel. It was a life changer — no more fatigue!"

Alison felt T3’s effects quickly: "Within a week of adding 20 mcg of Cytomel, the brain fog lifted. It was like someone pulled the curtain back and everything was clear again. "

Some people report improvements in mood and concentration while on T3.

Linda started taking a small dose of Cytomel: “The first day I noticed the brain fog lifted and I was able to make decisions and pay attention again. Within a couple of days, I had less joint pain and more muscle strength. My sleep improved. After six weeks, I reported to the doctor that on the 1-10 scale, I was about a 12! Mood swings were gone, too. I strongly recommend trying T3 to feel 'normal' again!”

Steffany noticed some improvements after starting Armour Thyroid.

“My dosage and all blood work are well-monitored. I don’t have regular fatigue, my hair stopped falling out and has grown back, my antibodies are in a normal range finally (initially the lab couldn’t even measure them; they were over 2,000). My skin is supple and not overly dry. I can even lose weight with moderate exercise and a somewhat flexible diet.”

Melissa had radioactive iodine RAI for Grave’s disease, and spent her 20s taking levothyroxine, experiencing depression, joint pain, and weight gain. She found a holistic nurse practitioner who prescribed natural thyroid.

“Two weeks after starting natural desiccated thyroid, my face literally shrunk — I wasn’t swollen anymore. About 25 pounds melted off, and my joint pain nearly disappeared. I can think clearly again. I am no longer exhausted to the point of despair. “

Because T3 drugs can be stimulating to the heart, T3 drugs are not recommended:

• If you have had a heart attack or any current or past history of heart disease
• If you are over 70

T3 is also not typically added during pregnancy, unless you are already stabilized on a thyroid hormone replacement treatment with T3. Research shows that T3 doesn’t effectively cross the placenta to provide much-needed thyroid hormone to your growing baby.

Unlike levothyroxine, T3 is very short-acting and can function like a stimulant.

The signs that you are getting too much T3 include a high pulse rate, heart palpitations, nervousness and anxiety, insomnia, and high blood pressure.

Sandy was a patient who did not feel well with T3: “We tried Nature-throid and Synthroid with Cytomel. Unfortunately, I got severe insomnia that wouldn't go away until I stopped and went on Synthroid only.”

If you find T3 drugs overstimulating, you can:

• Stop taking a T3 drug.
• Replace Cytomel or generic liothyronine with a time-released compounded T3 medication.
• Try NDT.
• Split one dose into two to three smaller doses taken throughout the day.

The American Thyroid Association’s official guidelines for the treatment of hypothyroidism say that only levothyroxine (synthetic T4) treatment is recommended. As a result, don't be surprised if your doctor (1) refuses to test T3 levels, and/or (2) refuses to treat you with T3. You may need a more open-minded healthcare practitioner, or a more innovative endocrinologist, to successfully pursue T3 testing and hypothyroidism treatment.