Hypothyroidism (an underactive thyroid) is treated by replacing the thyroid hormone your body is no longer making enough of. The standard first-line option is levothyroxine, a synthetic version of the hormone T4. Other approaches — liothyronine (synthetic T3), a combination of T4 and T3, and desiccated (natural) thyroid extract — exist and are used more selectively, usually under specialist guidance. This page compares the options so you can have a more informed conversation with your own clinician. It is general information, not medical advice, and it does not name doses.
The hypothyroidism medication options at a glance
Your thyroid normally makes mostly T4, which the body converts into the more active hormone T3 as needed. The treatments below differ mainly in which hormone they supply and how steadily they release it.
| Option | How it works | Best suited for | Route / frequency (general) | Key cautions |
|---|---|---|---|---|
| Levothyroxine (T4) | Supplies synthetic T4; the body converts it to T3 as needed, mimicking normal physiology. | Most adults with an underactive thyroid; the standard first-line choice. | Oral tablet, usually once daily, taken consistently (often on an empty stomach). | Narrow margin between too little and too much; absorption affected by some foods, supplements and medicines; needs periodic blood tests. |
| Liothyronine (T3) | Supplies active T3 directly, bypassing the T4-to-T3 conversion step. | Selected cases considered by a specialist, sometimes alongside T4. | Oral; shorter-acting, so levels can rise and fall more through the day. | Short duration of action makes levels harder to keep steady; caution in heart disease and in older adults; not routine first-line. |
| Combination T4 + T3 | Provides both hormones, aiming to mirror the mix a healthy thyroid makes. | Some people who still feel unwell on T4 alone, explored under specialist care. | Oral; dosing individualised and monitored closely. | Trial evidence is limited and mixed; major guidelines do not recommend it routinely. |
| Desiccated (natural) thyroid extract | Made from dried animal thyroid; contains a fixed ratio of T4 and T3. | Occasionally requested; considered only under specialist guidance. | Oral tablet derived from animal-gland extract. | Fixed T4:T3 ratio doesn't match human physiology; historically variable potency; not endorsed as first-line by major guidelines. |
Why levothyroxine is the usual starting point
Bodies such as the American Thyroid Association, the UK's NICE and the NHS describe levothyroxine as the treatment of choice for most people. It is long-acting, so one steady daily dose keeps hormone levels relatively even; it has been studied for decades; and because your body converts T4 to T3 on demand, it lets your own tissues regulate how much active hormone they use. For these reasons it is the option most clinicians reach for first. You can read more about the condition in our thyroid health hub and about how common thyroid disease is.
Where T3, combination and desiccated extract fit
Liothyronine (T3) and combination T4/T3 are generally considered only when someone keeps feeling unwell despite blood tests suggesting their levothyroxine is adequate. Because T3 acts quickly and wears off faster, blood levels are harder to keep steady — one reason it is not a routine first choice, particularly for older adults or people with heart conditions. Desiccated (natural) thyroid extract, made from animal thyroid, delivers a fixed blend of T4 and T3 that does not match the ratio the human thyroid produces, and its potency has historically been less consistent. Whether any of these alternatives might suit you is a decision for a specialist to weigh, not something to change on your own.
How treatment is monitored
Thyroid replacement is guided by how you feel plus blood tests — most often TSH, sometimes with free T4 or free T3. Levels are usually rechecked after any change and then periodically once stable. Our plain-language guide to understanding a TSH result can help you read your report, and how long until it works explains why thyroid medicines take weeks, not days, to show their full effect. Because thyroid hormone influences the heart, bones, and weight and metabolism, both under- and over-replacement carry risks — which is why steady monitoring matters. If you are also navigating menopause, thyroid and menopause symptoms can overlap, so testing helps tell them apart. At-home kits are increasingly common; our guide on what to look for in at-home thyroid tests explains their limits.
Hyperthyroidism is treated differently
Everything above is about an underactive thyroid. An overactive thyroid (hyperthyroidism) is not treated with hormone replacement at all. The main options a clinician may discuss are antithyroid medicines (which lower hormone production), radioactive iodine (which reduces thyroid activity), and, in some situations, surgery. The right choice depends on the underlying cause and is decided case by case.
Talk to your clinician
There is no single "best" thyroid medication for everyone — the right option depends on your diagnosis, your other health conditions, how you feel, and your blood results. Use this comparison to frame questions rather than to make changes; never start, stop or switch a thyroid medicine on your own. If you want to prepare, our doctor-visit report tool can help you organise symptoms and questions to raise. Then talk to your clinician, who can tailor treatment and monitoring to you.
