Thiazolidinediones (TZDs)

If you have not already done so, please read my introduction page (HERE).



Ok, so before we start, let’s address the elephant in the room.  How in the world do we pronounce Thiazolidinedione?  Like this (thigh-ah-ZO-li-deen-DYE-own).  No fun, huh?  So let’s just say TZDs like everyone else, lol!

How do TZDs work?

TZDs increase insulin sensitivity (lower insulin resistance).  I have read much information on exactly how this occurs and the consensus seems to be that this drug causes the formation of new fat cells.  Since the cells are new, they are still sensitive to insulin, thus they can take up glucose and lower glucose in the blood. This is particularly helpful in Type 2, diabetes, where the hallmark feature is insulin resistance.  Although not typically prescribed for those with Type 1 diabetes, some with Type 1 on larger doses of insulin, or who may have become insulin resistant, may also benefit.

This drug should not cause hypoglycemia as it does not lower blood glucose DIRECTLY.

This drug has an average A1c lowering capability of 0.5 – 1.0% (1).

Drugs in this class:  Actos (pioglitazone) and Avandia (rosiglitazone).

This drug class is also combined with metformin in some parts of the world.

Because of significant “Black Box” warnings in relation to this class of drug, it has somewhat fallen out of favor.  Also because metformin, which can often accomplish the same goals more effectively, has become so much more widely used and more cost effective with less side effects. However, for those that cannot take metformin, this drug class is sometimes prescribed as an alternative.

Common Precautions:

The most common side effects of this drug class is weight gain (think “new fat cells”).  This is a significant problem as those it is targeted to help typically already have weight control issues. In addition, there is an increased risk of peripheral fractures with this drug class, so it may cause concern for those with that are older, which is also a significant part of the target audience with Type 2.

Serious Precautions:

As mentioned, this drug class carries serious warnings.  An earlier generation of this drug was associated with significant liver damage.  Although this appears to have resolved, serious warnings exist.  TZDs may CAUSE or WORSEN congestive heart failure.  Monitor for fluid retention, swelling and weight gain.  Drugs in this class can also INCREASE risk for bladder cancer.

My Opinions

If you are only interested in the facts about this drug and how it works, feel free to stop here.  The following are my concerns with this drug class and my personal opinions.


Please note, in providing my personal opinions with concerns for these medications, once again, these are my opinions only and not intended as advice for you personally.  Please consult your personal healthcare provider to discuss the benefits and risks of any medications prescribed for you.

So, here are my thoughts.

Although the effects of this medication is similar to metformin, the A1c lowering ability is very un-impressive compared to metformin.  In addition, the likely serious side effects make this drug class just too dangerous.  As stated in our discussion of metformin, insulin resistance is most effectively addressed with a low carbohydrate diet along with exercise and other lifestyle factors…

REMEMBER, above all, diabetes is a problem of GLUCOSE INTOLERANCE.  The answer to that problem is not “take in all the glucose you want and then take a drug to deal with the excess glucose load.”  That is like telling someone with lactose intolerance to “eat all the milk and cheese you want and we’ll give you a pill to try and make it better.”  No!  People with lactose intolerance are told not to eat milk and cheese.  It is the same with diabetes.  People with diabetes should consume as little of the foods that turn quickly into glucose as possible.  Then, there will be little need for pills to deal with excess glucose.

As you know, I recommend a low carb lifestyle for all people, but PARTICULARLY as a first line of defense in the treatment of diabetes, NOT drug therapy.

(Why A Low Carb Diet Should Be the FIRST Approach in the Treatment of Type 2 Diabetes HERE.  Low Carb Diet Recommended for Type 1 and Type 2 Diabetes HERE.)

I believe that drug therapy has it’s place, but ONLY to address any issues after a healthy, low carb lifestyle, exercise and other lifestyle practices are ALREADY in place.  So, if you are already practicing these things, this class of drug may be unnecessary.  However, in some circumstances, long term insulin resistance may not be able to be fully overcome with lifestyle measures alone.  In my discussion on metformin, I did concede that metformin may be beneficial for this use.  Nevertheless, I still do not believe that the dangers of TZD’s out-weigh any SMALL potential benefits.  You could probably achieve the same A1c lowering affects as this drug after practicing a low carb lifestyle for just a few weeks.  And with the potential serious health risks, just seems logical to avoid this drug class.

Once again, this is my personal opinion.

To further my opinion, I would not personally feel comfortable taking any drug in this class.  There ARE medications that I would take to treat diabetes if my low carb healthy lifestyle was not enough to control my blood glucose.  None of the drugs in this class are among those I would consider.

Here is an extremely well-researched article by a website which I highly respect, expressing additional concerns about this drug class HERE.