Is Synthroid or Cytomel Better for Hypothyroidism?
Key takeaways:
Synthroid (levothyroxine) and Cytomel (liothyronine) are both medications for hypothyroidism. But there are important differences between them.
Synthroid contains levothyroxine (lab-made T4) and is the first-choice option for treating low thyroid hormone levels. Cytomel contains liothyronine (lab-made T3) and is usually only prescribed when Synthroid isn’t effective or well tolerated on its own.
Synthroid and Cytomel are both available as brand-name medications as well as lower-cost generics. GoodRx can help you access brand-name Cytomel at an exclusive cash price of $35.10. And you can save over 80% off the average retail price of generic Synthroid and Cytomel at certain pharmacies with a free GoodRx discount.
Table of contents
Hypothyroidism is a condition that affects many different parts of your body, from your heartbeat to your energy levels. It’s caused when your thyroid hormone levels are too low.
Synthroid (levothyroxine) and Cytomel (liothyronine) are two of the most popular medications for hypothyroidism. They both contain thyroid hormones to help restore your levels to normal. But which one works better? And is one safer? We’ll answer these and other common questions below.
What is hypothyroidism?
Your thyroid gland normally makes two types of thyroid hormone: triiodothyronine (T3) and thyroxine (T4). T4 is the main form of thyroid hormone in the body. It’s converted into T3 by the liver and kidneys. T3 is considered the “active” form of thyroid hormone. It's the hormone that does the final work — managing body temperature, mood, and energy levels, among various other effects.
At the right levels, thyroid hormones help keep the processes in your body balanced. But if levels are too high (hyperthyroidism), you may feel hot, irritable, and your heart may beat faster than normal.
Hypothyroidism, on the other hand, may make you feel sluggish and tired. You may also experience weight gain, constipation, or feel colder than usual. Women with hypothyroidism may have irregular menstrual bleeding and difficulty getting pregnant.
How do Synthroid (levothyroxine) and Cytomel (liothyronine) work?
Both Synthroid and Cytomel replace your natural thyroid hormones when levels are low. While the end result is the same, there are some differences in how they work.
Synthroid (levothyroxine) contains T4
Synthroid contains a lab-made (synthetic) version of T4. Your body converts Synthroid into T3 in the same way as T4 produced by your thyroid gland.
A dose of Synthroid can last up to several weeks in your body. Its long-lasting effect allows you to take Synthroid just once a day to keep your T3 levels stable. But it takes longer to work when you first start taking it. That’s because T4 has to be converted into T3 by the body before it becomes active. It takes about 4 to 6 weeks for Synthroid to reach its full effect.
Cytomel (liothyronine) contains T3
In contrast, Cytomel contains the synthetic version of T3, the active form of thyroid hormone. Since Cytomel is already in the active form of thyroid hormone, it can start working within a few hours of taking it. It also takes less time for Cyotmel to reach its full effect — about 1 to 2 weeks. But it doesn’t last as long in your body, so it can’t keep T3 levels as stable as Synthroid does.
Is Synthroid more effective than Cytomel?
Yes. The American Thyroid Association recommends Synthroid or its generic form, levothyroxine, as a first-choice treatment for hypothyroidism. The main reasons for this are:
Synthroid is well absorbed and provides stable thyroid hormone levels when taken once a day.
Synthroid is easily converted into T3 by the body.
Synthroid provides a thyroid hormone ratio of T4 to T3 that mimics what the body naturally produces.
But Cytomel still has a role in managing hypothyroidism for some people. Sometimes, Synthroid isn’t enough to return thyroid hormone levels to normal. Cytomel is sometimes taken in combination with Synthroid. Cytomel may also be prescribed for people who don’t absorb Synthroid well or have a negative reaction to it.
Some people still feel the symptoms of hypothyroidism while taking Synthroid, even if their thyroid hormone levels are normal. Some healthcare providers will add Cytomel treatment to see if it helps resolve these symptoms. This treatment is gaining popularity, but there isn’t a lot of evidence behind it. And the American Thyroid Association doesn’t recommend it.
Is Synthroid or Cytomel safer?
Both medications are considered safe when prescribed under the supervision of your healthcare provider at the right dosage. They’re even safe for children and while you’re pregnant (though Synthroid is preferred during pregnancy).
Synthroid and Cytomel also share similar side effects and risks. The most common problems happen if your dose is too high. This can cause hyperthyroidism, with symptoms such as:
Fast heart rate
Nervousness
Shaking
Diarrhea
Thin skin
Problems sleeping
Unintended weight loss
Sweating and feeling hot all the time
To avoid these symptoms, your healthcare provider will likely start you on a low dose and slowly increase it based on how your thyroid hormone levels respond. But if you notice these symptoms during your treatment, report them to your healthcare provider right away.
Can you take Synthroid or Cytomel for weight loss?
No. Both medications have a boxed warning, the most serious type of warning the FDA gives for medication. It warns that typical doses aren’t effective for weight loss, and larger doses can be life-threatening.
If you’re interested in medication options for weight loss, talk to your healthcare provider. Thyroid medications aren’t a safe option to consider.
How should I take Synthroid and/or Cytomel?
Figuring out the right dose for you will likely take some time. But the best way to help the process is to take your thyroid hormone medication correctly. In most cases, you’ll take Synthroid or Cytomel once a day. And it’s best to take them at the same time every day on an empty stomach.
It’s recommended to take Synthroid in the morning, about 30 minutes to 1 hour before breakfast and at least 4 hours before or after other medications. While this is the ideal way to take Synthroid, it may not work for everyone. Bedtime dosing may be just as effective as morning dosing, and easier for some people to remember.
The main goal is to take your thyroid hormone medication the same way every day. This includes time of day, how far apart from other medications, and how far apart from meals. Staying consistent will help your levels stay where they should be. If you make changes to how or when you take your medication, be sure to let your healthcare provider know. They may want to run some tests to see if a change in dose is needed.
Do Synthroid and Cytomel interact with other medications?
Yes. Synthroid and Cytomel are both extremely sensitive to many other medications, vitamins, and even some foods. Be sure to tell your healthcare provider about any other medications and supplements you take. They’ll let you know if there is an interaction and how to space them apart from your thyroid medication.
Some medications, supplements, and foods may cause thyroid medications to be less effective. These include:
Proton pump inhibitors like omeprazole (Prilosec)
Heartburn medications, such as famotidine (Pepcid)
Cholestyramine (Prevalite)
Grapefruit juice
Soybean flour
Cottonseed meal
Walnuts
Dietary fiber
Thyroid medications can, in turn, affect how well other medications work. For example, Synthroid and Cytomel may affect your blood glucose levels when you start taking them. Your provider may need to adjust the dose of any diabetes medications you take to ensure your blood glucose levels stay under control.
On the other hand, if you take a blood thinning medication, Synthroid and Cytomel can enhance their effects. Your provider may need to lower your blood thinner dosage to prevent bleeding-related side effects.
Does it matter if I take a brand or generic?
As mentioned, Synthroid and Cytomel are lab-made replacements for thyroid hormones, and everyone responds to them differently. You’ll need to find the right thyroid medication and dose that fits your body.
Both Synthroid and Cytomel are available as lower-cost generics. Whether the brand name or generic form is better depends on what your healthcare provider recommends and what works best for you.
But once you find the thyroid medication that works, it’s important to stick with it. You shouldn’t switch from brand to generic (or vice versa), or even from one generic manufacturer to another. This is because even though brand and generic thyroid medications share the same active ingredient, they aren’t all made exactly the same way. A small difference between manufacturers can change how your body absorbs the medication — which affects your thyroid hormone levels.
Sometimes, your pharmacy may change to a different manufacturer, especially for generic versions of thyroid medications. You may notice this if the tablet looks slightly different or has different markings on it than usual. If this happens, ask if there’s a way to get the type of medication you normally take. If it’s not available, let your healthcare provider know. They may want to perform lab tests to make sure your thyroid hormone levels stay stable on the new form of medication.
How to save on Synthroid and Cytomel
Synthroid and Cytomel are available as brand-name medications. But you can also find them as lower-cost generics. GoodRx can help you navigate the many ways to save on your prescription.
Save with GoodRx. Anyone with a valid prescription, regardless of insurance status, can use GoodRx to purchase a 30-day supply of brand-name Cytomel at an exclusive cash price of $35.10. GoodRx can also help you save over 80% off the average retail price of the generic versions of Synthroid and Cytomel. Generic Synthroid’s price at certain pharmacies is as low as $9.33 with a free GoodRx discount. Generic Cytomel’s price at certain pharmacies is as low as $25.23 with a GoodRx discount.
Save with patient assistance programs. If you’re uninsured or underinsured, you may be eligible for Synthroid and Cytomel patient assistance programs, which offer the medication at no charge.
Save with a copay savings card. If you have commercial insurance and meet eligibility requirements, brand-name Synthroid is as little as $25 if you use the manufacturer’s savings card.
The bottom line
Synthroid and Cytomel are both medications that treat hypothyroidism, but they’re not the same. Synthroid contains T4, and is the first-choice treatment option for low thyroid hormone levels. Cytomel contains T3, and is typically only used when Synthroid isn’t effective or well tolerated on its own.
Both medications should be taken on an empty stomach separately from other medications. This helps your body absorb them better. Whether you take Synthroid, Cytomel, or their generics, it’s best to stick with the same type and manufacturer every month. This helps you avoid minor differences between brands and keeps your thyroid hormone levels stable.
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References
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De Mello, R. B., et al. (2022). Evaluation of bedtime vs. morning levothyroxine intake to control hypothyroidism in older patients:A pragmatic crossover randomized clinical trial. Frontiers in Medicine.
Jonklaas, J., et al. (2014). Guidelines for the treatment of hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement. Thyroid.
PD-Rx Pharmaceuticals, Inc. (2023). Liothyronine sodium- liothyronine sodium tablet [package insert].
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