A new study from medical researchers at Harvard and Northwestern shows that 18- to 25-year-olds who smoke marijuana—even just recreationally!—had marked abnormalities in areas of their brains that regulate emotion and motivation
For those young people — and their parents — who think that smoking pot in moderation isn’t harmful, it’s time to think again.
A study released this week by researchers from Northwestern University’s Feinberg School of Medicine and Harvard Medical School has found that 18- to 25-year-olds who smoke marijuana only recreationally showed significant abnormalities in the brain.
“There is this general perspective out there that using marijuana recreationally is not a problem — that it is a safe drug,” says Anne Blood, an assistant professor at Harvard Medical School and the co-senior author of the study, which is being published in the Journal of Neuroscience. “We are seeing that this is not the case.”
The scientists say theirs is the first study to examine the relationship between casual use of marijuana in young people and pot’s effects on two parts of the brain that regulate emotion and motivation. As such, it is sure to challenge many people’s assumptions that smoking a joint or two on the weekends is no big deal.
It has certainly challenged mine. In a piece earlier this year, based on other research from Northwestern on the effects of heavy marijuana use, I suggested that young people should hold off on smoking pot as long as possible because their brains are still developing and the earlier the drug is taken up, the worse the effects. That remains good advice. Yet the truth is, I’ve not only been telling my own 16-year-old son to hold off, I’ve also been counseling him that should he ever decide to use pot, he should do so with temperance.
This “everything in moderation” mantra has always struck me as more realistic than preaching total abstinence. Baked into my message, meanwhile, has been the implicit belief that smoking a little weed on the weekends is no worse than having a few beers — a notion that many Americans apparently share.
A nationwide NBC/Wall Street Journal poll conducted last month found that only 8% of adults think that marijuana is the most harmful substance to a person’s overall health when lined up against tobacco, alcohol and sugar. In contrast, 49% of those surveyed rated tobacco as the most harmful on the list, while 24% mentioned alcohol. Notably, even sugar — at 15% — was considered more harmful than pot.
The new Northwestern-Harvard study punches a hole in this conventional wisdom. Through three different methods of neuroimaging analysis, the scientists examined the brains of 40 young adult students from Boston-area colleges: 20 who smoked marijuana casually — four times a week on average — and 20 who didn’t use pot at all.
Each group consisted of nine males and 11 females. The pot users underwent a psychiatric interview to confirm that they were not heavy or dependent marijuana users.
“We looked specifically at people who have no adverse impacts from marijuana — no problems with work, school, the law, relationships, no addiction issues,” says Hans Breiter, a professor of psychiatry and behavioral sciences at the Feinberg School and co–senior author of the study.
The scientists examined two key parts of the brain — the nucleus accumbens and the amygdala, which together help control whether people judge things to be rewarding or aversive and, in turn, whether they experience pleasure or pain from them. It is the development of these regions of the brain, Breiter says, that allows young people to expand their horizons, helping them appreciate and enjoy new foods, music, books and relationships.
“This is a part of the brain that you absolutely never ever want to touch,” Breiter asserts. “I don’t want to say that these are magical parts of the brain — they are all important. But these are fundamental in terms of what people find pleasurable in the world and assessing that against the bad things.”
Breiter and his colleagues found that among all 20 casual marijuana smokers in their study — even the seven who smoked just one joint per week — the nucleus accumbens and amygdala showed changes in density, volume and shape. The scientists also discovered that the more pot the young people smoked, the greater the abnormalities.
The researchers acknowledge that their sample size was small and their study preliminary. More work, they say, needs to be done to understand the relationship between the changes to the brain they found and their impact on the day-to-day lives of young people who smoke marijuana casually.
“The next important step is to investigate how structural abnormalities relate to functional outcomes,” says Jodi Gilman, an instructor at Harvard Medical School who collaborated on the study.
This is especially important, she and her colleagues add, in light of the growing push to legalize recreational marijuana use across America. “People think a little marijuana shouldn’t cause a problem if someone is doing O.K. with work or school,” Breiter says. “Our data directly says this is not so.”
"If you’re a cannabis user and you’re trying for a baby ... stop."
This advice comes from Dr. Allan Pacey, senior lecturer in andrology at the University of Sheffield in the United Kingdom and lead author of a new study that suggests using marijuana could increase a man's risk of fertility problems.
The study, published in the journal Human Reproduction, looked at how a man's lifestyle affects his sperm morphology: the size and shape of sperm. Researchers collected data from 1,970 men who provided semen as part of a fertility assessment.
All of the lifestyle information was self-reported, and researchers made no attempt to confirm accuracy. Of those men, 318 produced abnormal sperm, where less than 4% of it was the correct size and shape (as defined by the World Health Organization). The remaining men's sperm had a higher percentage at a "normal" size and shape.
"Cannabis smoking was more common in those men who had sperm morphology less than 4%," Pacey said. "Cannabis affects one of the processes involved in determining size and shape. And we also know that the way cannabis is metabolized is different in fertile and infertile men."
The study found that men who had less than 4% normal sperm were typically under 30 years old, had used marijuana within three months of giving their sample and were twice as likely to have provided their sample during the summer.
Any of those factors could have influenced sperm morphology, but Pacey said "the only thing we found that was a risk that a man can do something about was cannabis."
The researchers did not set out to study cannabis; they were simply collecting data about men’s lifestyles to identify risks to fertility. They looked at a number of possibilities, including cigarettes, alcohol, recreational drug use, employment history, BMI, medical history and the type of underwear the men wore. The researchers concluded that none of these were factors.
A third of all infertility cases are linked to the male partner, according to theAmerican Society for Reproductive Medicine (PDF). The society says marijuana is associated with impaired sperm function and should not be used by men trying to conceive.
Society President Rebecca Sokol says the study confirms previous studies that found a possible but not proven link between abnormal semen and sperm function and the use of cannabis. But she warns that the study does not have enough cases to draw definite conclusions.
"The take-home lesson of the article is that clinicians should counsel their patients on the possible relationships between lifestyle factors, abnormal semen parameters and fertility outcomes," Sokol said. "This should include a discussion that the data are often inconclusive, but the motto 'everything in moderation' is a wise approach for the couple who is planning a pregnancy."
Another paper on the health consequences of cannabis was published this week in the New England Journal of Medicine. Dr. Nora Volkow, director of the National Institute on Drug Abuse, and a team of the institute's researchers prepared a paper detailing the risks based on the strongest scientific evidence currently available. According to the paper, they wanted to dispel "the popular notion that marijuana is a harmless pleasure" and does not need to be regulated.
The paper details what the research shows are the adverse effects of recreational use, including the risks of addiction. Approximately 9% of those who try marijuana will become addicted; one in six of those who start as teenagers and 25% to 50% of those who smoke daily become addicted.
The researchers also wrote about the harmful effects of cannabis use on brain development, especially in kids and teenagers. Preliminary research shows that adolescents who are early-onset smokers are slower at tasks, have lower IQs later in life and have an increased incidence of psychotic disorders.
Other problems associated with marijuana use, according to the paper, include impaired short-term memory and motor coordination, altered judgment, effects on school performance, a higher risk of motor-vehicle accidents and higher risk of cancer and other health issues like heart disease and stroke.
"There is a widespread and growing perception among not only youth, but the public in general, that marijuana is a relatively harmless drug, and it has been difficult marshaling science to correct this perception," Volkov said. "The science of marijuana is far from settled, and this has allowed advocates of various positions to cherry-pick evidence to support their particular stance."
The review also lists some of the potential therapeutic benefits of cannabis. Conditions and symptoms that may be helped by marijuana treatment include glaucoma, chronic pain, multiple sclerosis, epilepsy, nausea, inflammation and AIDS-related anorexia and wasting syndrome, according to the report.
Volkow and her fellow researchers fear that as governments begin to modify marijuana policy toward legalization, recreational use will increase, as will a host of negative health problems.
However, Mason Tvert, communications director at the Marijuana Policy Project, says the report by the National Institute on Drug abuse researchers is not an objective review of current scientific evidence.
The Marijuana Policy Project has worked to reform marijuana policies and laws since 1995 at both the federal and state level. It lobbies for legislation that would replace marijuana prohibition in favor of legal regulation. It provided much of the staff and funding in the push to legalize and regulate marijuana for adults 21 and older in Colorado in 2012, and its goal is to pass, by 2017, at least 10 more laws that would regulate cannabis like alcohol.
"NIDA has long been criticized for prioritizing politics over science," Tvert said. "They fail to acknowledge any of the well-known research that refutes, and in some cases completely debunks, their conclusions. This more closely resembles a poorly written college essay ... than it does an objective, evidence-based journal article. Every objective study on marijuana has concluded that it poses far less harm than alcohol to the consumer and to society."
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