Marijuana may double stroke risk in young adults

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Marijuana, the most widely used illicit drug, may double stroke risk in young adults, according to research presented at the American Stroke Association's International Stroke Conference 2013.

In a New Zealand study, ischemic stroke and transient ischemic attack (TIA) patients were 2.3 times more likely to have cannabis, also known as marijuana, detected in urine tests as other age and sex matched patients, researchers said.

"This is the first case-controlled study to show a possible link to the increased risk of stroke from cannabis," said P. Alan Barber, Ph.D., M.D., study lead investigator and professor of clinical neurology at the University of Auckland in New Zealand. "Cannabis has been thought by the public to be a relatively safe, although illegal substance. This study shows this might not be the case; it may lead to stroke."

The study included 160 ischemic stroke/TIA patients 18-55 years old who had urine screens upon admission to the hospital. Among the patients, 150 had ischemic stroke and 10 had TIAs. Sixteen percent of patients had positive drug screens, mostly male who also smoked tobacco.

Only 8.1 percent of controls tested positive for cannabis in urine samples. Researchers found no differences in age, stroke mechanism or most vascular risk factors between marijuana users and non-users.

In previous case reports, ischemic stroke and TIAs developed hours after cannabis use, Barber said. "These patients usually had no other vascular risk factors apart from tobacco, alcohol and other drug usage."

It's challenging to perform prospective studies involving illegal substances such as cannabis because "questioning stroke and control patients about cannabis use is likely to obtain unreliable responses," Barber said.

In the study, the regional ethics committee allowed researchers to use urine samples from other hospitalized patients. But researchers knew only the age, sex and ethnicity for matching due to a lack of consent.

The study provides the strongest evidence to date of an association between cannabis and stroke, Barber said. But the association is confounded because all but one of the stroke patients who were cannabis users also used tobacco regularly.

"We believe it is the cannabis and not tobacco," said Barber, who hopes to conduct another study to determine whether there's an association between cannabis and stroke independent of tobacco use. "This may prove difficult given the risks of bias and ethical strictures of studying the use of an illegal substance," he said. "However, the high prevalence of cannabis use in this cohort of younger stroke patients makes this research imperative."

Physicians should test young people who come in with stroke for cannabis use, Barber said.

"People need to think twice about using cannabis," because it can affect brain development and result in emphysema, heart attack and now stroke, he said.


  1. Malcolm Kyle Malcolm Kyle Netherlands says:

    In this Auckland University study, all but one of the stroke patients who were cannabis users also used tobacco regularly.

    The author (Dr. P. Alan Barber) openly admits that the study didn't account for tobacco use —how long and how much the young stroke patients had been smoking and how big a role that might have played in stroke risk. The "study" also relied on urine samples, but traces of THC can be found in the urine for at least a whole month after consumption of cannabis.

    According to the US National Stroke Association, "Smoking tobacco (at least)doubles the risk for stroke when compared to a non-smoker. It reduces the amount of oxygen in the blood, causing the heart to work harder and allowing blood clots to form more easily."

    "Prohibitionists are scraping the bottom of the barrel by claiming that cannabis doubles the risk of stroke, when this result has already been linked to tobacco use. There is nothing scientific about this study and it should be discredited by all rational individuals."
    —Norml president Julian Crawford

    "Narcotics police are an enormous, corrupt international bureaucracy … and now fund a coterie of researchers who provide them with ‘scientific support’ … fanatics who distort the legitimate research of others.… The anti-marijuana campaign is a cancerous tissue of lies, undermining law enforcement, aggravating the drug problem, depriving the sick of needed help, and suckering well-intentioned conservatives and countless frightened parents."   —William F. Buckley, commentary in The National Review, April 29, 1983, p. 495

    Here is Dr. David Allen, a Heart and Stroke specialist, calling for cannabinoid-based medicines to be used throughout America. Not just in emergency rooms and through prescriptions, but also through the ingestion of the whole plant, daily, as a supplement to diet:

  2. Peter Reynolds Peter Reynolds United Kingdom says:

    Professor Alan Barber, lead investigator for the study, said "All but one of the stroke patients who were cannabis users also used tobacco regularly". Tobacco is a proven cause of stroke. This study is fundamentally flawed.

    Prof. Barber's claim that "We believe it is the cannabis and not the tobacco." is disgraceful, unscientific and provides an insight into the true motivation of those conducting this type of 'research'. It isn't genuine scientific research, it's an attempt to produce propaganda to support prohibitionist policies.

    There is far more peer reviewed evidence to show that cannabis is neuroprotective against stroke, brain trauma and neurodegenerative disease

  3. Joel Dalais Joel Dalais United Kingdom says:

    Cannabis has been so widely used throughout the last 100 years, and the last 5,000 years, that any decent scientist can easily run up a study to show 'association' between Cannabis and an issue. The same as any decent scientist could draw up an association between any issue and a persons emotional state. It's an easy open blind bet.

    Your single source is evident of 0 critical analysis of which is needed in any piece to be taken seriously.

    The people are not stupid anymore, they're waking up, but nice try ;)

    Cannabis effects emotional states, calming, lessening anxiety, depression, stressful thoughts. It's also an inflammatory that works on the brain, the main reason for stroke is inflamation of the brain, inflamed parts interfere with other parts of the brain (blocking oxygen), or they rupture (disrupting the flow).

    But hey, believe what you will, there's a reason that it's not Cannabis users not dying in there 100's of thousands, the minority clinging to an archaic law and belief will soon realise as their numbers unfortunately dwindle with the 'legal' drugs and the wars committed in the name of the 'war on drugs' (aka, greed).

    CLEAR Media Team
    CLEAR - Cannabis Law Reform

  4. lee prew lee prew United Kingdom says:

    "Sixteen percent of patients had positive drug screens, mostly male who also smoked tobacco."

    "These patients usually had no other vascular risk factors apart from tobacco, alcohol and other drug usage."

    Oh okay! So it must be the cannabis that is the trigger for potential strokes. Not alcohol, tobacco or other drug use. This study sounds 110% legit to me.

  5. Jordan Dillon Jordan Dillon United States says:

    “We’re talking about fried foods, french fries, hamburgers, processed meats, hot dogs,” bacon, ham, liver, gizzards, and sugary drinks, said the study’s leader, Suzanne Judd of the University of Alabama in Birmingham.

    People who ate about six meals a week featuring these sorts of foods had a 41 percent higher stroke risk than people who ate that way about once a month, researchers found.

    In contrast, people whose diets were high in fruits, vegetables, grains, and fish had a 29 percent lower stroke risk.

    “It’s a very big difference,” Judd said. “The message for people in the middle is there’s a graded risk,” meaning the likelihood of suffering a stroke rises in proportion to each Southern meal in a week.

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
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