Proponents of legalizing marijuana have long stood by claims of the plant's overall safety, but new research raises questions about pot's impact on the cardiovascular system and brain.
Writing this past week in the Journal of the American Heart Association, medical scientists in France concluded that recreational marijuana use may result in cardiovascular-related complications, and possibly even death, among young and middle-aged adults.
In a separate study earlier this month, two teams of scientists in this country examined the effects of marijuana among young casual users and found distinct brain abnormalities directly traceable to pot.
The new research arrives as the debate sharpens in Albany and lawmakers fight over whether New York should become the 21st state to legalize marijuana for medicinal purposes.
Gov. Andrew M. Cuomo is opposed to a broad medical marijuana program despite an increasing number of legislators here -- and in other states -- who support such a plan. They are joined by advocates for patients with cancer, epilepsy and a wide range of other devastating disorders.
Popular wisdom has long held that marijuana is good medicine, but studies are revealing a gloomier side to the drug.
"We identified several remarkable cases of cardiovascular complications as the reasons for hospital admission of young marijuana users," Dr. Émilie Jouanjus, of the Centre Hospitalier Universitaire de Toulouse in France, said in a statement last week.
Jouanjus and colleagues discovered in a study group of 1,979 adults who had a history of marijuana use, most of them men who ranged in age from their 20s through early 50s, that nearly 2 percent had heart complications. The average age of patients was 34.
For instance, 20 users suffered heart attacks; 10 had peripheral vascular disease, marked by damage to blood vessels in the limbs. Three had damage to arteries that supply blood to the brain. Nine patients, the study said, died of cardiovascular complications.
While heart attacks and other cardiovascular complications are found frequently in large populations everywhere, these cases were unique, Jouanjus said, because the people were, for the most part, quite young.
"This unexpected finding deserved to be further analyzed, especially given that the medicinal use of marijuana has become more prevalent and some governments are legalizing its use."
Dr. Scott Krakower, assistant unit chief of psychiatry at the Zucker Hillside Hospital in Glen Oaks, said research about marijuana's deleterious effects have been overshadowed by popular ideas about its beneficial profile.
"Marijuana got that profile because it has definitely been helpful for pain," Krakower said. "It has analgesic effects."
But in addition to cardiovascular disorders, the plant has been linked to addiction, lung cancer and neuro-cognitive problems, he said, noting those concerns "got pushed aside as the pain-control issue was pushed to the front."
Krakower said Jouanjus' research isn't the first to raise concern about the plant's potential to cause vascular problems.
In January, scientists from New Zealand reported that marijuana users have a higher risk of stroke compared with people who do not use the drug.
Krakower thinks physiological risks linked to marijuana correlate with repeated usage.
Marijuana does have an addiction potential, said Krakower, who is on the substance abuse and addiction committee for the American Academy of Child and Adolescent Psychiatry.
"Adolescent marijuana users are more likely to develop marijuana dependence," he said.
Meanwhile, a joint team of researchers from Northwestern and Harvard universities proved earlier this month that young adults who use marijuana casually develop significant abnormalities in two key brain regions important to emotion and motivation.
The study, published in the Journal of Neuroscience, is the first to demonstrate that recreational marijuana use is related to major brain changes. Smokers, on average, used the drug once or twice a week.
"This study raises a strong challenge to the idea that casual marijuana use isn't associated with bad consequences," said Dr. Hans Breiter, co-author of the report.
Krakower, who is on the board of directors of the Greater Long Island Psychiatric Society, said he's not surprised by the results. "We have known for some time that marijuana [use] causes changes in the brain."