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A year ago last week, New York legalized the recreational use of marijuana. Officials predict legal sales will begin by the end of this year.

Marijuana is neither as benign as some proponents claim nor as dangerous as detractors allege, experts say. Cannabis can help treat some medical conditions, but it also carries risks, especially for heavy users and adolescents.

Here are responses to questions about marijuana and its potential health effects.

Is marijuana more or less dangerous than alcohol?

“On the whole, marijuana is probably less dangerous than alcohol, and certainly less dangerous than fentanyl and opioids and the like, but we do have to recognize that you can take your use of a less-harmful substance to an incredibly harmful level,” said Dr. Kevin Hill, director of addiction psychiatry at Beth Israel Deaconess Medical Center in Boston and an associate professor of psychiatry at Harvard Medical School.

About 10% of cannabis users develop an addiction, compared with about 15% of people who drink alcohol and a quarter of those who use opioids, said Hill, author of “Marijuana: The Unbiased Truth about the World’s Most Popular Weed.” If you use marijuana multiple times a day, every day, you may have “cannabis use disorder,” he said.

For those with the disorder, “It can wreak havoc on their lives,” just like alcohol and other drugs can, destroying relationships and careers, he said.

A year ago this week, New York State legalized the...

A year ago this week, New York State legalized the recreational use of marijuana. Credit: AP/Mathew Sumner

What about adults who use marijuana occasionally?

“Most people who use cannabis don’t have a problem, just like most people who drink alcohol don’t have an addiction problem,” Hill said.

Studies have linked cognitive and physical health problems with marijuana use, but those studies typically are of heavy users, he said. “For people who are able to use occasionally, it really hasn’t borne out that it’s problematic,” Hill said.

Even so, someone who, for example, never used marijuana and accidentally ingests it in a cookie at a party could experience a panic attack or psychosis, said Dr. Andrew Monte, an associate professor of emergency medicine at the University of Colorado Anshutz Medical Campus and a medical toxicologist who has studied cannabis.

“Anyone can have an adverse event to marijuana no matter how little they take if they’re not used to it,” Monte said.

Dr. Andrew Monte, associate professor of emergency medicine, University of Colorado...

Dr. Andrew Monte, associate professor of emergency medicine, University of Colorado Anshutz Medical Campus. Credit: University of Colorado School of Medicine

Edible marijuana is a particular problem, even in those who have used cannabis before, because it has a delayed reaction, Monte added. Some people eat more and more because they’re not yet feeling high, and then they can get so high that it can lead to a psychiatric episode, he said.

Is marijuana a 'gateway drug' to harder drugs such as heroin?

“There is no evidence that cannabis is a gateway drug,” said R. Lorraine Collins, associate dean for research and professor in the School of Public Health and Health Professions at the University at Buffalo, and a member of a National Academies of Sciences, Engineering and Medicine committee that released a 2017 report on marijuana and health. “The notion that using one drug leads you to another is not substantiated by science.”

What types of physical and mental health problems are linked to marijuana?

The National Academies report said evidence suggests that smoking marijuana regularly can lead to chronic cough and bronchitis episodes. It’s unclear if it can lead to worsened lung function, but evidence suggests it doesn’t increase the risk of lung cancer. Some evidence indicates cannabis could be linked to greater risk of a heart attack, but more research is needed. More data also is needed about other potential health effects, such as on the immune system, the report said.

Monte said heavy users are at risk of a condition that leads to severe, repeated vomiting.

In addition, marijuana — especially daily use — is linked with greater risk of depression, anxiety and psychosis, he said.

Why hasn’t there been more research on marijuana’s health effects?

Even though 37 states allow regulated medical use of marijuana, the federal government still classifies marijuana as a “Schedule One” substance, deemed to have no medical benefit. Collins said that “doesn’t make sense,” and it makes it more difficult to do research on the potential benefits and negative effects of marijuana.

What are medical benefits of marijuana?

“We have quite a bit of data showing that THC may be helpful for chronic pain,” said Ziva Cooper, director of the UCLA Cannabis Research Initiative and a member of the National Academies health report committee. THC is the chemical in marijuana that gets users high. 

Ziva Cooper, director, UCLA Cannabis Research Initiative.

Ziva Cooper, director, UCLA Cannabis Research Initiative. Credit: UCLA Health

The report said chronic pain patients “were more likely to experience a significant reduction in pain symptoms” when treated with cannabis.

“In respect to the aches and pains people may have here and there on an acute basis, we don’t know necessarily if the chemicals in cannabis might be helpful,” Cooper said.

Although THC sometimes is used for insomnia or anxiety, more research is needed to show whether it really helps, she said.

The Food and Drug Administration approved synthetic THC to treat nausea and vomiting in people with cancer on chemotherapy and to increase appetite in people with AIDS with “wasting syndrome.” The agency also approved an oral form of CBD for some types of seizures.

Dr. Kevin Hill, director, addiction psychiatry, Beth Israel Deaconess Medical...

Dr. Kevin Hill, director, addiction psychiatry, Beth Israel Deaconess Medical Center, Boston. Credit: McLean Hospital

What about marijuana’s effects on adolescents and young adults?

The most important period of brain development is through age 25, and “to the extent the brain’s development is disrupted in some fashion by the use of drugs — cannabis is one; alcohol is another — then it can influence what you learn, how easy it is to learn, whether you are somebody who can master more complicated information versus simpler information,” Collins said. “The implications are long term.”

The dangers for young people increase with the amount they use, Hill said. But an adolescent who starts using marijuana sparingly is at more risk than an adult of eventually becoming addicted, he said.

“I have a 14-year-old daughter,” Hill said. “If she were using cannabis, there’s a one-in-six chance that she’d go on to develop a problem with it. I don’t want to take those chances.”

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