What is the difference between Cytomel and Cyno... - Thyroid UK

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What is the difference between Cytomel and Cynomel? Does anyone take these?

Tuxi1 profile image
12 Replies

Wondering too if the ingredients are the same?

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Tuxi1
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fuchsia-pink profile image
fuchsia-pink

Different countries have different T3 brands, so these are both T3 medication. I think cynomel is what you find in France and cytomel what you get in the US. The fillers in different brands may be different. Some members report different overseas brands as being of slightly varying strength - but I get mine on the NHS so can't compare lio as prescribed in the UK with either.

Tuxi1 profile image
Tuxi1 in reply to fuchsia-pink

What brand of T3 do you get on the NHS?

fuchsia-pink profile image
fuchsia-pink in reply to Tuxi1

Liothyronine. Mostly Teva. Haven't noticed any difference at all when I've had another brand [my very first prescription was tablets in a bottle, from the hospital, with no mention of brand or patient leaflet so not sure what that was]. Note the Teva problems often cited here are for the levo, not the lio

helvella profile image
helvellaAdministratorThyroid UK

Cytomel was the brand name of the first US liothyronine. Registration seems to have started in 1955 in the US, approved in 1957, by King Pharmaceuticals in Canada (now a subsidiary of Pfizer). Re-registered by King in US in 1997.

However, also registered in Israel by UK's Smith Kline Beecham in 1992. And in the Netherlands by Ace Pharma in 2019.

Cynomel was first registered in 1956 and there have been multiple subsequent registrations:

*1957 Smith Kline & French Canada in Canada

*1956 SmithKline Beecham (Australia) in Australia

1957 Smith Kline & French International (India) in India.

*1975 SmithKline Beckman (Costa Rica) in US

*1981 Smith Kline & French (France) in US

1991 Glaxosmithkline (France) in US

2008 Laboratorios Grossman (Chile) - no country identified

2010 Laboratorios Grossman (Costa Rica) in Mexico

* - inactive

www3.wipo.int/branddb/en/

The names Cytomel and Cynomel are, like Coca Cola and Pepsi Cola, just brands.

You must always check the excipients of the specific medicine you are considering. Ace Pharma and King (Pfizer) Cytomel products are made to different formulations in different countries. Grossman and Sanofi Cynomel products are made to different formulations in different countries.

However, at least all Cytomel and Cynomel products have the same active ingredient. In other medicines this is not the case. Especially cough and cold relief products which, even when supplied by one company, often have different active ingredients by market and by time.

It is because of this complexity of brand names that we tend to prefer using the recommended International Non-proprietary Names - in this case, Liothyronine. Then identify the company and country involved.

The common use of the phrase "generic for" in the US is less satisfactory.

Hibs1 profile image
Hibs1 in reply to helvella

I got the Ace brand of Cytomel via Roseway labs on private script. PIL in Dutch so assumed same ingredients. Wrong! After reached full dose,12.5, started getting bloated, checked ingredients and it has a really bad additive, croscamellose sodium, which expands 20x it's size in colon! Not recommended for those with gastrointestinal disorders in particular. I complained as I paid for original brand

helvella profile image
helvellaAdministratorThyroid UK in reply to Hibs1

Shame I didn't know you wanted that information in English. :-(

I have a copy of the original Public Assessment Report from Netherlands in English:

dropbox.com/s/vme09hfp5c8gu...

The excipients are gelatin (E441), croscarmellose sodium (E468), calcium sulfate dihydrate and magnesium stearate (E470b).

Hibs1 profile image
Hibs1 in reply to helvella

Yes. I figured it out when I read the patients leaflet. I did finish them but the bits of tablet were lodged in my colon for a week after I finished them, hope not tmi? The ingredients weren't on their website and rather interesting the tablet description was different from website as in the 25 mcg tablets should have crossed score but they didn't , just the one score same as smaller doses.

helvella profile image
helvellaAdministratorThyroid UK in reply to Hibs1

They changed the scoring of the 25 microgram tablets at some point. (Somewhere they explain this!) This was to permit splitting in four. The single score tablets were not approved for more than a single split.

(Just for reference: score or break lines do NOT on their own imply a tablet can be safely split fr dosing purposes unless the accompanying information says so.)

Hibs1 profile image
Hibs1 in reply to helvella

So I wonder if it was old stock I had as it just had dingle split. Who knows?(Ps did hey prescribed all nhs t3 first but am so sensitive to fillers that gave up with them)

helvella profile image
helvellaAdministratorThyroid UK

More information about thyroid hormone medicines here:

helvella - Thyroid Hormone Medicines

I have created, and try to maintain, a document containing details of all thyroid hormone medicines in the UK and, in less detail, many others around the world.

dropbox.com/s/shcwdwpedzr93...

Tuxi1 profile image
Tuxi1 in reply to helvella

Wow Helvella that's so detailed! Well done! If cytomel does that to your bowels then I will be really sunk - better avoid. From what I understand Cynomel has different ingredients?

helvella profile image
helvellaAdministratorThyroid UK in reply to Tuxi1

But there are two different products called Cytomel and another two different products called Cynomel! All four are different to each other. :-)

All these things are patient-specific - many might be fine on all of them.

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