What Are Thiazolidinediones (TZDs)? Diabetes Medicines

What it means

Thiazolidinediones, often called TZDs or glitazones, are a class of diabetes tablets. Examples include pioglitazone. They work mainly by making muscle, fat and liver cells more sensitive to insulin, so the body uses its own insulin better and blood sugar falls. They are used for type 2 diabetes, often with other diabetes medicines, and work slowly over weeks.

TZD labels carry a boxed warning about heart failure, because these medicines can cause the body to hold on to fluid, which can cause or worsen heart failure. Signs to report include rapid weight gain, swelling of the ankles or legs, and breathlessness. Labels also mention bone fractures, swelling (edema), eye swelling at the back of the eye (macular edema) and, for pioglitazone, a possible bladder cancer risk.

TZDs are different from sulfonylureas, which make the pancreas release more insulin, and from metformin. On their own, TZDs do not usually cause low blood sugar, but this can happen when combined with insulin or sulfonylureas.

Where you may see it

• Boxed warnings on pioglitazone labels about heart failure
• Diabetes medicine leaflets under 'Serious side effects'
• Diabetes clinic medication lists