The Food and Drug Administration has announced that it will require the manufacturers of new diabetes drugs to conduct more thorough testing to ensure that they do not increase the risk of cardiovascular problems. The agency says that the new standards will be immediately applied to all diabetes drugs that are under development.

Concerns about the cardiovascular risks of diabetes drugs arose in 2007 when a study published in the New England Journal of Medicine found that patients taking Avandia were more likely to suffer heart problems. Researchers found that Avandia users were 64% more likely to die from heart problems and 43% more likely to suffer a heart attack. The FDA later added a “black-box” warning to the drug’s label in order to alert doctors and patients of the increased risk of Avandia side effects.

Under the new guidelines, the developers of new diabetes drug must demonstrate “that a new therapy does not increase cardiovascular risk to an unacceptable extent” when compared with approved treatments. Previously, companies were only required to show that drugs lowered blood sugar.

As a result of the new guidelines, companies will have to include patients with a higher risk of heart problems in their studies, such as elderly patients or those with kidney problems. As a result, late-stage studies that now take six months to complete could now take up to a year to complete under the new rules, the FDA says.