Tirosint vs. Synthroid: Differences, similarities & side effects

In this article:

• Tirosint vs. Synthroid: Key differences
• Tirosint vs. Synthroid: Conditions treated
• Is Synthroid better than Tirosint?
• Tirosint vs. Synthroid: Insurance coverage and cost comparison
• Tirosint vs. Synthroid side effects
• Tirosint and Synthroid interactions
• Tirosint and Synthroid drug warnings

In this article

• Tirosint vs. Synthroid: Key differences
• Tirosint vs. Synthroid: Conditions treated
• Is Synthroid better than Tirosint?
• Tirosint vs. Synthroid: Insurance coverage and cost comparison
• Tirosint vs. Synthroid side effects
• Tirosint and Synthroid interactions
• Tirosint and Synthroid drug warnings

Tirosint and Synthroid are two brand-name medications used to treat hypothyroidism (an underactive thyroid) and thyroid cancer. They are classified as thyroid replacement hormones and work by replacing thyroid hormones that are normally produced by the body. Although both medications are known as thyroid hormone replacement medications, they have some differences, as we will discuss below.

Tirosint vs. Synthroid: Key differences

Tirosint and Synthroid are both brand-name drugs. Tirosint is available in capsule and liquid form. Its liquid form is called Tirosint-Sol. Both the Tirosint capsules and Synthroid tablets are available in generic formulations, but Tirosint-Sol liquid does not have a generic version. Both medications come in various doses, as shown in the chart below. These medications are approved for use in adults and children.

Tirosint vs. Synthroid: Conditions treated

Thyroid hormone is part of the endocrine system and plays a large role in metabolism, growth, and development. The term “thyroid hormone” actually represents a combination of the two main hormones released by the thyroid—a small, butterfly-shaped gland at the front of your neck. Those two hormones are thyroxine (T4) and triiodothyronine (T3).

T4 is mostly inactive, and T3 is active. When the thyroid releases T4, the body converts it into T3 in order to use it. Tirosint and Synthroid both replace the amount of T4 that the body is missing. These medications are often prescribed by primary care providers or endocrinologists to treat an underactive thyroid or thyroid cancer. Symptoms of hypothyroidism may include:

• Fatigue
• Weight gain
• Intolerance to cold
• Joint pain 
• Muscle pain
• Dry skin
• Hair loss or thinning hair
• Irregular or heavy periods
• Fertility problems
• Slow heart rate
• Depression 

Tirosint capsules, Tirosint-Sol, and Synthroid can be used along with surgery and radioactive iodine to manage a type of thyroid cancer called thyrotropin-dependent, well-differentiated thyroid cancer. They can also be used to treat primary, secondary, or tertiary hypothyroidism:

• Primary hypothyroidism is caused by a condition that directly impacts the thyroid, causing it to create insufficient levels of thyroid hormone. One common cause is  Hashimoto’s thyroiditis.
• Secondary hypothyroidism is caused by failure of the pituitary gland.
• Tertiary hypothyroidism is caused by failure of the hypothalamus and can be congenital (inherited) or acquired. 

Tirosint-Sol and Synthroid can be used in adults and children of any age, including infants. Tirosint capsules can be used in adults and children 6 years and older.

Is Synthroid better than Tirosint?

Because both drugs contain the same active ingredient, levothyroxine, they work the same and are similarly safe and effective. Many hypothyroid patients prefer generic Synthroid (levothyroxine) due to the reasonable cost. However, patients with certain conditions like Celiac disease or sensitivities or allergies to certain inactive ingredients may prefer Tirosint. The inactive ingredients in Tirosint capsules are gelatin, glycerin, and water. Synthroid contains more excipients (inactive ingredients) and fillers such as lactose and dyes.

Regardless of which drug you take, the dosage is important. You will be monitored on a regular basis to make sure your T4 and thyroid-stimulating hormone (TSH) levels are within normal limits. The dosage will depend on many factors, including age, weight, other medical conditions you have, and other medications you take that may interact with Tirosint or Synthroid. 

Only your healthcare provider can determine which medication is best for you. Consult your provider for more information and medical advice on thyroid replacement therapy with Tirosint, Synthroid, or other forms of levothyroxine such as Unithroid, Levoxyl, or generic levothyroxine.

Tirosint vs. Synthroid: Insurance coverage and cost comparison

Generics tend to be covered at a lower price, so keep that in mind when you check with your health insurance provider for pricing estimates and out-of-pocket costs. If you prefer the brand-name drug, you will likely have a higher copay. However, you can check the manufacturers’ websites for savings programs like copay cards and other ways to save on brand-name Tirosint or Synthroid. 

A typical out-of-pocket price for brand-name Tirosint capsules without insurance would be about $189 for a one-month supply of 50 mcg capsules. With a SingleCare coupon, you could save about $49. 

A typical out-of-pocket price for brand-name Synthroid without insurance is approximately $79 for a one-month supply of 50 mcg tablets. With a SingleCare coupon, you could save $30. 

If you opt for generic levothyroxine sodium instead of Tirosint or Synthroid, you could pay $25 for 30, 50 mcg capsules and as little as $3 with a SingleCare coupon.  

* Cost is subject to change and depends on pharmacy, location, and dosage.

Tirosint vs. Synthroid side effects

Side effects of Tirosint and Synthroid are generally due to a dose that is too high, which causes symptoms of hyperthyroidism (overactive thyroid). These side effects may include:

• Irregular heartbeat
• Heart attack
• Shortness of breath
• Muscle spasms or weakness
• Headache
• Nervousness
• Irritability
• Trouble sleeping
• Shaking
• Increased appetite
• Weight loss
• Diarrhea
• Intolerance to heat
• Irregular menstrual periods
• Rash

Keeping your regular follow-up appointments with your healthcare provider and getting your blood tests on schedule will enable your provider to prescribe the appropriate dose, which can minimize side effects.

Some patients may also notice temporary hair loss when starting the medication. 

This is not a full list of side effects, and others may occur. Consult your healthcare provider for more information and a full list of side effects. 

Tirosint and Synthroid interactions

Before you take Tirosint or Synthroid, tell your healthcare provider about all the medicines you take, including prescription drugs, over-the-counter medicines, vitamins, and supplements. Let your doctor know if you take any medications for your heart, blood pressure, or diabetes. 

Certain medicines, vitamins, and supplements, such as iron and antacids, must be taken at least four hours before or after your thyroid medication. 

Also, certain foods and beverages may interact with the absorption of levothyroxine in people with thyroid disease or thyroid cancer. This includes soybean flour (found in infant formula), cottonseed meal, walnuts, dietary fiber, and grapefruit, including grapefruit juices. Avoid consuming these ingredients within an hour of taking Tirosint or Synthroid.

This is not a full list of interactions. Consult your healthcare professional for more information about drug and food interactions and how they may affect you. 

Tirosint and Synthroid drug warnings

Both drugs have a boxed warning, also called a black box warning, the most serious warning required by the Food & Drug Administration. The warning states that thyroid hormones, including Tirosint and Synthroid, should not be used to treat obesity or for weight loss. The warning also notes that higher doses than needed can cause serious or life-threatening toxic effects. Always take the dosage that your healthcare provider prescribes. Do not take more medication than prescribed. Dosages of these medications are individualized to the patient based on many individual factors, including lab values, age, weight, diagnosis, other medical conditions the patient has, and other medications the patient takes. 

Before taking Tirosint or Synthroid, tell your healthcare provider about any medical conditions you have, including if you are pregnant or breastfeeding or have an adrenal gland disorder, heart problems, diabetes, or any others. 

Other warnings include:

• In older adults and people with heart disease, healthcare providers will start treatment at a lower dose to avoid the risk of heart-related side effects, including atrial fibrillation.
• People who take Tirosint or Synthroid will be carefully monitored with blood tests to measure thyroid hormone levels and ensure proper dosing.
• Tirosint and Synthroid should not be used to treat myxedema coma (severe hypothyroidism with organ involvement).
• Thyroid medication may affect blood sugar levels in people with diabetes. Close monitoring and a possible dosage change in diabetes medication or insulin may be needed.
• Over-replacement of thyroid hormone can result in decreased bone mineral density. Healthcare providers will prescribe the lowest effective dose in order to minimize the risk of side effects.