Thyroid UK
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Synthroid vs Levothyroxine

I was taking 150mcg thyroxine and 20 liothyronine and have recently changed to 150 synthroid with the 20 liothyroning. My symptoms have worsened if anything so wanted to know if 150mcg thyroxine and synthroid the same, or is one more potent than the other. I have also ordered some cytomel to see if that is better for me with the synthroid than the liothyronine. I would prefer not to try NDT as I am vegetarian


3 Replies

Pinkgirl, Synthroid is a USA brand which may have different fillers to the UK generic Levothyoxine you were taking. Synthroid is often used as a 'generic' term for Levothyroxine in the USA so you may need to check you are using branded Synthroid. Check the patient information leaflet for trademarks and the list of ingredients/fillers.

The active ingredient should be the same whatever brand you are using but patients often experience improvement/worsening symptoms when they switch brands which may be due to formulation/fillers.

I'd be inclined to sort out T4 before switching to Cytomel else you won't be able to figure out what is causing/improving symptoms.


Hi Clutter,

Thanks for your reply. The brand that I have is Eutirox and it didn't have a patient info leaflet. However, on the box it says: Formula which I think is the same as ingredients, and each tablet contains levothyroxine sodium of 150mcg. They are produced by Merck. Definitely a genuine product as have trademark on them and on the blister packs inside the box.

I see what you mean about not changing to Cytomel


Pink, check out Merck's website for Eutirox ingredients. Members have found it beneficial to switch between Mercury Pharma, Actavis and Wockhardt, the three UK generics, and it's often due to the different fillers used and the way the tablets are formulated.


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