Smoking marijuana may significantly raise the risk of stroke and heart failure, scientists including one of Indian origin have found. While previous marijuana research has focused mostly on pulmonary and psychiatric complications, the new study is one of only a handful to investigate cardiovascular outcomes, researchers said.

"Like all other drugs, whether they're prescribed or not prescribed, we want to know the effects and side effects of this drug," said Aditi Kalla, Cardiology Fellow at the Einstein Medical Centre in the US. "It's important for physicians to know these effects so we can better educate patients, such as those who are inquiring about the safety of cannabis or even asking for a prescription for cannabis," said Kalla.

Coming at a time when marijuana, medically known as cannabis, is on track to become legal for medical or recreational use in more than half of US states, the study sheds new light on how the drug affects cardiovascular health. The study included the health records of patients admitted at more than 1,000 hospitals comprising about 20 per cent of US medical centres.

Researchers extracted records from young and middle-aged patients - age 18-55 years - who were discharged from hospitals in 2009 and 2010, when marijuana use was illegal in most states. Marijuana use was diagnosed in about 1.5 per cent (316,000) of more than 20 million health records included in the analysis.

Comparing cardiovascular disease rates in these patients to disease rates in patients not reporting marijuana use, researchers found marijuana use was associated with a significantly increased risk for stroke, heart failure, coronary artery disease and sudden cardiac death.

Marijuana use was also linked with a variety of factors known to increase cardiovascular risk, such as obesity, high blood pressure, smoking and alcohol use. After researchers adjusted the analysis to account for these factors, marijuana use was independently associated with a 26 percent increase in the risk of stroke and a 10 per cent increase in the risk of developing heart failure.

"Even when we corrected for known risk factors, we still found a higher rate of both stroke and heart failure in these patients, so that leads us to believe that there is something else going on besides just obesity or diet-related cardiovascular side effects," Kalla said. "More research will be needed to understand the pathophysiology behind this effect," he said.

Research in cell cultures shows that heart muscle cells have cannabis receptors relevant to contractility or squeezing ability, suggesting that those receptors might be one mechanism through which marijuana use could affect the cardiovascular system. It is possible that other compounds may be developed to counteract that mechanism and reduce cardiovascular risk, Kalla said.