If you’ve been diagnosed with hypothyroidism — an underactive thyroid — you may have come across two very different approaches to treatment: levothyroxine and natural desiccated thyroid (NDT). They’re often talked about as if they’re interchangeable, but they aren’t quite the same thing. This guide explains the difference in plain English. It is general information only and is not medical advice — any treatment decision is one to make with your doctor.
A quick recap: what the thyroid does
Your thyroid gland produces two main hormones: thyroxine (T4) and triiodothyronine (T3). T3 is the more biologically active of the two. The body makes mostly T4 and converts it into T3 in the tissues as it needs it. In hypothyroidism, the gland doesn’t make enough of these hormones, which can cause tiredness, weight gain, low mood, feeling the cold and more.
What is levothyroxine?
Levothyroxine is a synthetic version of T4. It is the standard, first-line treatment for hypothyroidism in the UK and is recommended by NICE guidance. Once in the body it is converted to T3 in the same way as the body’s own T4. For most people, levothyroxine alone restores hormone levels and relieves symptoms — it is well understood, inexpensive and easy to dose. Thyrosit is one brand of levothyroxine; you can see Thyrosit here.
What is natural desiccated thyroid (NDT)?
Natural desiccated thyroid is made from dried (desiccated) porcine (pig) thyroid gland. Unlike levothyroxine, it contains both T4 and T3 together, in a fixed ratio. Thyroid-S is a widely used NDT product; you can see Thyroid-S here.
T4 vs T4+T3: the key difference
Levothyroxine supplies T4 only. The body normally produces both T4 and T3 and converts T4 into the more active T3 as needed. Most people convert well on T4 alone, but a minority report continued symptoms despite a normal TSH (thyroid-stimulating hormone) blood test — and the role of combined T4+T3 therapy, which NDT provides, is an active and sometimes contested topic in the clinical literature. Whether it is appropriate for you is a decision only your doctor can make with you.
Why isn’t NDT routinely prescribed on the NHS?
NDT is not licensed as a medicine by the UK’s Medicines and Healthcare products Regulatory Agency (MHRA), and current NICE and British Thyroid Foundation guidance does not recommend it for routine use, citing a lack of large-scale long-term evidence and the variability of older preparations. Some doctors do prescribe T3 or NDT on an individual (“named-patient”) basis where they judge it appropriate for a particular patient.
Talk to your doctor
Thyroid treatment is individual. Your TSH and other blood tests, your symptoms and your medical history all matter, and switching or combining treatments should always be supervised by a clinician — dosing of T3-containing products in particular needs care. If you’re not feeling well on your current treatment, that’s a conversation to have with your GP or endocrinologist rather than a change to make on your own.
This article is for general information only and does not constitute medical advice. Always consult a doctor or pharmacist before starting, stopping or changing any treatment.
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