Levothyroxine vs. Liothyronine for Thyroid Cancer and Hypothyroidism: Important Differences and Potential Risks.

Levothyroxine

Liothyronine

(Cytomel)

Summary for Levothyroxine

Prescription only

Levothyroxine is a thyroid hormone used to treat low thyroid hormone levels (hypothyroidism) in people of all ages. It's also approved to help treat thyroid cancer along with radioactive iodine and surgery. The medication is available in tablet and liquid forms and is taken once daily, usually on an empty stomach in the morning. Regular blood tests are needed to keep your dose in the right range. Common side effects happen when the dose is too high and can include fast heartbeat, anxiety, and weight loss.

Indications for Levothyroxine

Hypothyroidism (low thyroid hormone levels)
Thyroid cancer, together with radioactive iodine and surgery

Pros and Cons for Levothyroxine

Pros

First-choice medication for treating low thyroid hormone levels
Safe to use during pregnancy
Only needs to be taken once a day
Available as a liquid solution (Tirosint Sol, Thyquidity, and Ermeza)

Cons

Must be taken on an empty stomach
Might take several weeks to find the right dose
Requires regular blood tests
Interacts with many foods, medications, and supplements

Common Side Effects for Levothyroxine

Signs of having too much thyroid hormones in the body, such as:

Irregular heartbeat
Chest pain
Shortness of breath
Leg cramps
Headache
Nervousness
Hives or skin rash
Irritability
Trouble sleeping
Tremors
Muscle weakness
Change in appetite
Weight loss
Vomiting
Diarrhea
Sweating a lot
Sensitivity to heat
Fever
Changes in menstrual period

Warnings for Levothyroxine

Not for weight loss
Heart problems
Adrenal crisis in people with adrenal insufficiency
Worsening diabetes
Bone loss

Summary for Liothyronine

Prescription only

Liothyronine (Cytomel) is a thyroid hormone medication that can be used for a number of thyroid-related health concerns. More specifically, it's a lab-made form of the T3 thyroid hormone that's made by your thyroid gland. People of all ages can take this medication, and it's generally taken by mouth just once daily. Although weight loss is a potential side effect of liothyronine (Cytomel), it should not be taken solely for this purpose.

Indications for Liothyronine

Hypothyroidism (low thyroid hormone levels)
Thyroid cancer (with radiation and surgery)
Thyroid suppression test to help with diagnosis

Pros and Cons for Liothyronine

Pros

Acts faster than other thyroid hormone replacement therapies
Safe to use during pregnancy
Safe to use in children
Available as a lower-cost generic version

Cons

Requires regular blood tests and frequent dose adjustments at first to make sure you're getting the right dose
Has a risk for heart problems
Can't use if you have untreated adrenal insufficiency
Shouldn't be used to treat conditions that aren't related to abnormal thyroid function (e.g., benign thyroid nodules, nontoxic goiter, swelling of the thyroid gland caused by infection)