Taking nitrates for heart problems alongside erectile dysfunction drugs like Viagra or Cialis could be a prescription for trouble, a new study warns.

Men who combine the two types of medications have a higher risk of death or suffering a heart-related health emergency, researchers reported Jan. 15 in the Journal of the American College of Cardiology.

“Physicians are seeing an increase of requests for erectile dysfunction drugs from men with cardiovascular diseases,” said senior researcher Dr. Daniel Peter Andersson, an associate professor at the Karolinska Institute in Sweden. “Patients taking nitrates may experience an increased risk of negative health outcomes.”

Viagra, Cialis, Levitra and others are posphodiesterase type 5 inhibitors (PDE5i). They work by widening arteries and increasing blood flow to the penis.

Nitrates also work by dilating blood vessels, and are used to treat chest pain associated with angina and to ease symptoms of heart failure.

Both types of drugs can cause drops in blood pressure, so guidelines recommend they not be used together.

But researchers said the number of people prescribed both is growing, and there’s little real-world data on the implications of using them at the same time.

For this study, researchers analyzed health records for nearly 61,500 men prescribed nitrates who’d had a heart attack or had undergone a procedure to open blocked coronary arteries.

Among those men, more than 5,700 also had been prescribed an erectile dysfunction drug.

The data revealed that men taking both drugs had an overall higher risk of death, as well as of heart attack, heart failure and other major cardiovascular events.

Few events occurred within 28 days of men receiving an erectile dysfunction drug, indicating that there is low immediate risk, researchers said.

“Our goal is to underscore the need for careful patient-centered consideration before prescribing PDE5i medication to men receiving nitrate treatment,” Andersson said in an American College of Cardiology news release. “Furthermore, it justifies our efforts for continued research into the ambiguous effects of ED drugs on men with CVD [cardiovascular disease].”

In an accompanying editorial, Dr. Glenn Levine said erectile dysfunction drugs are reasonably safe in men with mild angina in good physical shape, but using them with an ongoing nitrate prescription is ill-advised at best.

“ED and CAD [coronary artery disease] are unfortunate, and all too common, bedfellows,” said Levine, a professor of cardiology with Baylor College of Medicine in Houston. “But, as with most relationships, assuming proper precautions and care, they can co-exist together for many years — perhaps even a lifetime.”