Is levothyroxine the same as Synthroid, Euthyrox or Eltroxin?

Qassi Gaba · 12 October 2026 · 5 min read

Yes, mostly. Synthroid, Euthyrox, Eltroxin, Eutroxsig, Levoxyl, Unithroid, Tirosint and Thyronorm are all brand names for the same drug: levothyroxine sodium, sold under a different name depending on which country and which manufacturer you're dealing with. Liothyronine is the exception. It's a different thyroid hormone, not a brand name for this one, and it isn't interchangeable with it.

If that answers your question, you can stop here. If you want to know what actually differs between these products, and why liothyronine is a separate thing, keep going.

What's actually in the bottle

Levothyroxine sodium is a synthetic version of thyroxine, the hormone your thyroid makes less of in hypothyroidism and Hashimoto's. The NHS page on levothyroxine describes it as replacement for a hormone your body isn't producing enough of, and the ATA's guidance on thyroid hormone treatment covers the same drug under its generic name. Every brand on that list, wherever it's sold, contains this same molecule.

What differs between brands is everything around the molecule: the manufacturer, the fillers and binders used to make the tablet, the country it's licensed in, and sometimes the form it comes in.

Same drug, different names by country

Pharmaceutical companies license and market the same drug under different names in different places, and thyroid hormone is a plain example of it. Synthroid, Levoxyl and Unithroid are all US brand names, and you can find their official labelling on DailyMed, the National Library of Medicine's repository of FDA-approved drug labels, by searching for Levoxyl or Unithroid by name.

Eltroxin is the name you'll hear in the UK, Ireland and parts of the Commonwealth. Euthyrox is common across much of continental Europe. Eutroxsig is sold in Australia. Thyronorm is a brand used in India. None of these is a different drug from the others. They're the same active ingredient, manufactured and licensed separately for each market, which is also why a prescription written in one country doesn't always translate neatly to a pharmacy in another.

Tirosint is slightly different in one respect worth knowing about: it's a gel capsule formulation rather than a tablet, with fewer of the dyes and fillers found in tablet forms. For some people with sensitivities to those additives, that's the reason it gets prescribed instead of a tablet brand. The active hormone is unchanged. You can check its own labelling by searching DailyMed for Tirosint.

"Levothyroxine sodium tablets" isn't a brand at all. It's the generic name, used when a pharmacy dispenses whichever manufacturer's version is in stock rather than a specific named brand. The active ingredient is identical to any of the names above.

Why the brand sometimes matters anyway

If the drug is the same, why does it sometimes matter which brand you're given? Because thyroid hormone replacement has a narrow margin between too little and too much, and small differences in how a tablet is absorbed, caused by the fillers rather than the hormone itself, can be enough to shift levels slightly in someone who is sensitive to it. This is part of why clinicians commonly advise sticking with the same brand once you've found one that works, rather than switching between generic manufacturers at the pharmacy's discretion. The ATA's page on thyroid hormone treatment covers the general principles of dosing and monitoring that this concern sits inside. Whether a brand switch is worth worrying about for you specifically is a question for whoever prescribes it, not something a blog post can answer for you.

Where liothyronine is different

Liothyronine isn't on the list above because it isn't a brand name for levothyroxine. It's a synthetic version of a different hormone: triiodothyronine, or T3, rather than thyroxine, or T4. Your thyroid makes both, but T4 is the one it makes more of, and the one the body converts into T3 as needed. NIDDK's overview of hypothyroidism describes T4 as the primary hormone measured and replaced; MedlinePlus's page on T3 testing covers the other one.

Liothyronine is sold under brand names such as Cytomel, and under its own generic name too, which you can look up on DailyMed. Some people take it instead of levothyroxine, some take it alongside levothyroxine as combination therapy, and most people on thyroid hormone replacement never take it at all. Which of those applies to anyone, if any, is a clinical decision that depends on things a blood test alone doesn't settle, and it isn't something this article is in a position to weigh in on.

What this means practically

If you've been switched from one of these names to another, you haven't necessarily been switched to a different drug. If you've been told you're taking "levothyroxine sodium" rather than a brand name, that's the generic version of the same thing you'd get under any of the brand names above. If you've been prescribed liothyronine in addition to one of them, that's a second, different hormone, not a second name for the first one.

Questions about whether switching brands matters for you, or whether combination therapy with liothyronine is something to ask about, belong with whoever is managing your treatment. What a label says and what published guidance covers are facts anyone can look up. What they mean for a specific person's dose is not.

Where this touches Haloscan

When you log your medication in Haloscan, it keeps the brand name as you entered it, separate from the dose and the date. That turns out to matter more than it sounds: if a pharmacy substitutes a different manufacturer's tablet between refills, having the brand name sitting next to your lab trend is often the only way to notice it happened at all.