Marijuana is being increasingly recognized for its health benefits. There’s strong evidence that medical marijuana can relieve chronic pain caused by arthritis or diabetic neuropathy and improve conditions as diverse as Parkinson’s disease, epilepsy, multiple sclerosis and inflammatory bowel disease. With the elderly, it may help with appetite and depression.

With all this good news about medical marijuana—and the increasing number of states that are making recreational marijuana legal—it’s easy to start thinking that marijuana is completely harmless and good for you. But a new study raises concerns about marijuana and one of the most common health problems that people face with aging—high blood pressure.

Background: Within just a few minutes of smoking marijuana, the heart rate speeds up—even doubles. That can last for several hours. The question is, could it have serious and even long-term cardiovascular effects?

Study: Researchers from the School of Public Health at Georgia State University used information from NHANES, a long-term study of a nationally representative sample of the population that includes interviews, questionnaires and medical exams. The researchers zeroed in on the 5,000 adults who had responded to a question about whether they had ever used marijuana in any form. The researchers also used data from the questionnaire to estimate how many years they had used marijuana. They then identified the 1,213 respondents who had died by 2011 and looked to see whether there was any link between the use of marijuana/hashish and death from cardiovascular conditions, including high blood pressure. About one-fifth of the participants (21%) reported that they had used marijuana—for nearly 12 years, on average.

Results: After adjusting for any previous diagnosis of high blood pressure, body mass index, cigarette smoking and other well-known risk factors for death from diseases related to high blood pressure, participants who used marijuana were more than three times more likely to die from diseases related to high blood pressure (such as stroke) than those who did not use marijuana. The longer the use of marijuana, the greater the risk for death, with 4% greater risk for each year of use.

Bottom line: This is a fairly small observational study, so it is far from definitive. As the authors note, it has limitations—including the fact that it’s based on a single question, so it can’t identify chronic daily users from occasional experimenters. It also does not home in on different kinds of marijuana-based products now available—smoking pot may have very different physiological effects from eating a marijuana edible or taking a tincture. Finally, tetrahydrocannabinol (THC), the euphoria-inducing compound in marijuana, may have different blood pressure effects than does cannabidiol (CBD), the noneuphoric marijuana compound responsible for many of marijuana’s therapeutic effects. Larger, longer and more detailed studies are clearly needed.

But it does inject a clear note of caution into the discussion. If you have high blood pressure and are considering marijuana for, say, chronic pain, talk to your doctor about your options. At a minimum, you and your doctor will likely want to keep a keen eye on your blood pressure readings over the next few weeks and months. As for recreational use of marijuana, it’s clear that we don’t know everything we should about the health effects of long-term, chronic use.