When you’re prescribed an ACE (angiotensin converting enzyme) inhibitor to reduce high blood pressure, you’re likely to hear about side effects such as dry cough, headaches, dizziness and fatigue. According to new research, lung cancer may be a frightening addition to that list.

ACE inhibitors, such as Lotensin, Vasotec, Prinivil, Zestril, Accupril and Altace, are used by millions of people. They’re not only very common and effective medications for lowering blood pressure, they’re also prescibed for conditions including heart disease, diabetes, kidney disease and migraine headaches.

Concern over a link between them and lung cancer isn’t new. But previous studies found mixed results. They also involved small numbers of participants who were followed for short periods of time.

This new study included almost one million patients who were newly started on a blood pressure drug. Within this group of patients, researchers compared the risk of developing lung cancer in patients on long-term ACE inhibitors with patients on an angiotensin receptor blocker (ARB), another type of high blood pressure medication. None of the patients had any cancer diagnosis at the start of the study.

Over the course of the decade-long study, just under 8,000 participants developed lung cancer, a rate of about 0.8%. Compared with patients on ARBs, patients on ACE inhibitors had a higher risk of developing lung cancer. This increased risk wasn’t evident until after five years on the drug, at which point it was 22% higher. At 10 years, it was 31% higher. Surprisingly, the risk increase was the same for smokers and nonsmokers.

What’s the connection between a drug designed to improve health and the deadliest cancer for men and women in the US? The researchers suspect that it may be the accumulation of a naturally occurring substance in the lung called bradykinin. Its role is to dilate blood vessels, which in turn reduces blood pressure. ACE inhibitors work by increasing bradykinin, but at the same time, bradykinin has been linked to the growth of lung cancer cells.

While the increased risk for lung cancer needs to be confirmed by other studies, if you’re on an ACE inhibitor or your doctor suggests that you start one, discuss the lung cancer risk, especially as it goes up over time, and whether an alternative is a safer option for you. Complicating the picture is that taking ACE inhibitors long-term has been shown to lower the risk for breast cancer.

If appropriate for your situation, you might be able to reduce your blood pressure with lifestyle changes—and these don’t carry any risks!