![[dr. bob]](/dr-bob-sm.gif)
Dr. Bob is Robert Hsiung, MD,
bob@dr-bob.orgShown: posts 1 to 5 of 5. This is the beginning of the thread.
Posted by Maxime on February 2, 2004, at 9:56:11
What is the difference between Cytomel and Synthroid? It seems like Synthroid is the most used for hypothyroidism.
Does anyone know the difference between the two?
Maxime
Posted by Ame Sans Vie on February 2, 2004, at 10:36:33
In reply to Synthroid or Cytomel -what's the diff, posted by Maxime on February 2, 2004, at 9:56:11
Cytomel is liothyronine sodium (aka L-triiodothryonine or LT3), a synthetic form of the T3 thyroid hormone. Synthroid is levothyroxine sodium (aka L-3,3',5, 5'-tetraiodothyronine or T4), also a synthetic thyroid hormone.
Both drugs are indicated for hypothyroidism, among other things. Beyond that, I couldn't really tell you the difference! I'm not sure if they can be used interchangeably or what... perhaps someone else could answer this.
Just FYI, there are also formulations that contain both T3 and T4 -- Thyrolar and Liotrix are the two that I know of.
Posted by Bill LL on February 2, 2004, at 16:33:58
In reply to Synthroid or Cytomel -what's the diff, posted by Maxime on February 2, 2004, at 9:56:11
Two years a go I could have answered your question. I do know that synthroid is T4 and cytomel is T3.
If memory serves, docs almost always give T4 since T4 eventually turns into T3 which is the active form of the hormone. I think docs give T3 if they think that a person has a problem converting T4 to T3.
Thyroid hormone is not only given to people for hypothyroidism. It is also sometimes prescribed to augment an antidepessant. When used for this purpose, the T3 form is usually given. However, some docs prefer to give a depressed patient both T3 and T4. This preparation is available in 2 forms; 1) a pill that combines T3 and T4 (such as thyrolar- I may have spelled it wrong) or 2) actual thyroid gland tissue from animals- called Armor thyroid.
If a depressed patient has a normal thyroid blood test (ie normal TSH which is less than or equal to 4) the addition of thyroid supplements will only help if the person is taking an antidepressant. It generaly will not help by itself.
Posted by Maxime on February 2, 2004, at 17:23:18
In reply to Re: Synthroid or Cytomel -what's the diff, posted by Bill LL on February 2, 2004, at 16:33:58
Thanks Bill. I am trying to understand as much as I can about hypothyroidism and the medications used and why.
I appreciate your response.
Maxime
Posted by noa on February 3, 2004, at 12:09:16
In reply to Re: Synthroid or Cytomel -what's the diff}}Bill, posted by Maxime on February 2, 2004, at 17:23:18
I think the other posters summed it up. I would only add that T4 is the more stable form of the thyroid hormone that the body is able to store. It is the one that is used by the pituitary to gauge how much TSH to send to the Thyroid gland to signal it to produce hormone. When there is a lot of T4 floating around, the need to produce more is low--ie, low TSH.
One of the problems is that when doctors use TSH and T4 as the only measures of whether someone is hypothyroid, they might draw an eroneous conclusion based on low TSH and adequate T4 if the problem lies in the person's difficulty converting the storage form of hormone--T4--to the active form of hormone--T3. So, some people need both T4 and T3 to reverse symptoms of hypothyroidism or to get antidepressants to work better.
BTW--Cytomel (T3), is shorter acting than Synthroid. This means that Cytomel doses might need to be split into two half-doses per day to avoid uneven surges of the hormone,which can possibly lead to heart palpitations, etc.
This is the end of the thread.
Psycho-Babble Medication | Extras | FAQ
Dr. Bob is Robert Hsiung, MD,
bob@dr-bob.org
Script revised: February 4, 2008
URL: http://www.dr-bob.org/cgi-bin/pb/mget.pl
Copyright 2006-17 Robert Hsiung.
Owned and operated by Dr. Bob LLC and not the University of Chicago.