People with type 2 diabetes have less sensitive insulin receptors in the cell membranes. Insulin must attach to a receptor in order for glucose to be able to leave the blood and enter the cell. Less-sensitive receptors mean insulin can't bind. And that means glucose can't get into the cell. The result is twofold. The level of glucose in the blood stays high, and the cells don't have the energy they need from glucose. Thiazolidinediones work by increasing the sensitivity of the insulin receptor sites in muscle, fat and liver cells. This allows more of the body's own insulin to bind with receptors. And that allows glucose to pass from the blood and into the body's cells. Since glucose can get into the cells, it can be used for energy. This type of diabetes pill also decreases the liver's production of glucose. Both of these actions work together to decrease the amount of glucose in the blood.

Possible Side Effects of Thiazolidinediones

Talk with your doctor if you think the drug is causing side effects. You may have these side effects when you take a thiazolidinedione:

  • anemia
  • body pain
  • swelling in your legs, ankles and feet, called edema
  • fatigue
  • headache
  • stomach upset
  • yellow color in your skin or the whites of your eyes, called jaundice
  • weight gain

Not everyone who takes thiazolidinediones will have these side effects. You should not be afraid to take your medicine because of the side effects listed. They are listed so that you can watch out for them and tell your doctor right away if you experience any of them.

In 2007, a warning was added to the packaging for thiazolinediones, stating that they can cause or worsen heart failure. Your doctor can tell you the latest information and help you decide if these medicines are a good choice for you.

Possible Drug Interactions With Thiazolidinediones

Before you take a thiazolidinedione, tell all your doctors and your pharmacist about all the medicines you take. Include medicines you take for your diabetes as well as for any other problem. Tell them about everything you take and how much you take each day, including all of the following:

  • prescription medicines
  • over-the-counter medicines
  • herbs
  • vitamin and mineral supplements

It's best to keep an updated list of these and bring a copy to give to your doctor. That way you can add to it whenever you take something new or delete the types you no longer take. Make a copy for each of your doctors so that they can keep it in your file. This complete list helps your doctor be better prepared to prescribe a thiazolidinedione that is the least likely to interact with your other treatments.

Many medicines can have harmful effects when you take them with other medicines. Always tell your doctor about all the medications that you take. Do not use any other medicine without your doctor's OK. Talk with your doctor before you take a thiazolidinedione if you take any other medications.

Written by award-winning health writer Bobbie Hasselbring

Reviewed by Beth Seltzer, MD

Last updated June 2008