Types of Thyroid Medication: Levothyroxine, T3, and NDT Explained

Levothyroxine (Synthroid, Euthyrox, generics) is first-line for nearly everyone with hypothyroidism. T3-only pills (Cytomel) and natural desiccated thyroid (Armour, NP Thyroid) are reserved for specific situations. Liquid and softgel forms (Tirosint) help patients with absorption problems. The right answer for most people is levothyroxine at the right dose.

The basics in plain language

Your thyroid normally makes two hormones: T4 (the storage form) and T3 (the active form). Your body slowly converts T4 into T3 as it needs it. When your thyroid stops making enough, you take a pill that gives the body what the gland no longer makes [C1][C6].

There are basically four families of thyroid medication you will hear about:

• Levothyroxine — a lab-made copy of T4. It is the same molecule your thyroid produces, just made in a factory. Brand names include Synthroid, Euthyrox, Levoxyl, and many generics. This is what almost everyone takes [C1].
• Liothyronine (T3) — a lab-made copy of T3, the active hormone. Brand name Cytomel. It acts fast and is short-lived, so it has to be taken several times a day. Reserved for specific cases [C1][C2].
• Natural desiccated thyroid (NDT) — dried, powdered thyroid gland from pigs. Brand names Armour Thyroid, NP Thyroid, Nature-Throid. It contains both T4 and T3. Older medication, divisive online, not first-line [C1][C3].
• Liquid and softgel levothyroxine — same T4 molecule, but in a form that does not need stomach acid to dissolve. Brand name Tirosint (softgel and oral solution). Used for patients who have trouble absorbing the standard tablet [C5].

If you were just diagnosed and feel overwhelmed by all of this, that is normal. The short version is: you almost certainly need only one of these — levothyroxine — and the rest of this article explains why.

What does this mean for me?

For nearly everyone with hypothyroidism (an underactive thyroid that no longer makes enough hormone) — including Hashimoto disease (the autoimmune condition that is the most common cause) — the American Thyroid Association recommends starting with levothyroxine alone [C1]. There are three good reasons:

1. It works for most people. When the dose is right, the body converts T4 to T3 on its own, the way your thyroid used to. Most patients feel well on levothyroxine alone [C1][C6].
2. It is predictable. Levothyroxine has a steady, long half-life (about 7 days), so one tablet a day keeps blood levels even. T3 is short-acting and produces peaks and valleys [C1][C2].
3. The evidence is strongest. Decades of trials support levothyroxine. Studies that have compared combination T4 + T3 therapy or NDT against levothyroxine alone have generally not shown clear benefit for symptoms, weight, or quality of life across the whole patient population [C2][C3][C4].

That last point is the one most patients have not heard. The internet is full of stories that NDT or T3 "changed everything." A small subset of patients may prefer them, but in randomized trials they did not consistently beat levothyroxine [C2][C3][C4]. NDT is also harder to dose precisely because the ratio of T4 to T3 in pig thyroid does not match human output [C1][C3].

What to expect when you start levothyroxine

Your endocrinologist or primary care doctor will pick a starting dose based on your weight, age, and heart history. Most adults reach full replacement at roughly 1.6 mcg per kilogram of body weight per day, though older patients and people with heart disease start lower and titrate up [C1].

You take one tablet a day, on an empty stomach, with water only. Wait 30 to 60 minutes before coffee or food [C1]. Levothyroxine takes about 4 to 6 weeks to reach a steady level in your blood, so your doctor will recheck TSH (the thyroid blood test) at 6 weeks and adjust the dose if needed [C1][C6]. Most patients land on their final dose within 2 to 3 adjustments.

If you have trouble with the standard tablet — gastritis, acid reflux on a PPI (proton-pump inhibitor, the strong heartburn medications like omeprazole), celiac disease, or bariatric surgery — your doctor may switch you to a liquid or softgel form like Tirosint, which absorbs even when stomach acid is low [C5].

What to skip / common pitfalls

A few things worth knowing before the internet talks you into them:

• NDT is not "more natural" in any meaningful sense. It is processed animal thyroid with variable hormone content. Levothyroxine is the exact T4 molecule your body makes [C1][C3].
• T3-only therapy is rarely the answer. It is reserved for narrow situations and is harder to dose safely [C2].
• Brand vs generic is real but usually small. The molecule is identical, but fillers can affect absorption slightly. If you do well on a brand, ask the pharmacy not to switch without telling your doctor, and recheck TSH 6 weeks after any switch [C1].
• "Glandular" supplements sold online are not regulated thyroid medication. They have inconsistent hormone content and should not replace prescription therapy [C2].

Frequently asked questions

Is levothyroxine the same as Synthroid? Yes. Synthroid is one brand name for levothyroxine. Euthyrox, Levoxyl, and unbranded generics are all the same active molecule [C1].

Will NDT or Armour make me feel better than levothyroxine? For most patients, no. Head-to-head trials have not shown that NDT consistently outperforms levothyroxine for symptoms or quality of life [C3][C4]. A minority do prefer it, but it is a second-line option to discuss with your endocrinologist, not a default.

Why did my doctor not prescribe T3? Because T3 alone or T4 + T3 combinations have not clearly beaten levothyroxine in randomized trials, and T3 has a short half-life that produces peaks and valleys in blood levels [C1][C2].

Will I need this medication forever? For Hashimoto disease and most permanent hypothyroidism, yes. The autoimmune process does not go away, and your gland continues to lose capacity over time [C1][C6]. The medication replaces what your thyroid used to make — one tablet a day, indefinitely.

Bottom line

Levothyroxine is the standard treatment and works for the vast majority of patients [C1][C6]. T3 and NDT are niche second-line options that have not consistently beaten it in trials [C2][C3][C4]. Liquid and softgel forms exist for real absorption problems [C5]. Most of the time, feeling better is about the right dose and giving your body 6 to 12 weeks to respond [C1].