Expert Commentary

Covering marijuana: Research roundup and 7 tips for journalists

As more states consider legalizing marijuana, consider these studies and tips on what's known and unknown about the health effects of cannabis products.

Photo by Elsa Olofsson on Unsplash

Originally published in April 2021, this piece about covering marijuana was updated on Oct. 7, 2022, with information about President Biden’s announcement pardoning anyone convicted of a federal marijuana possession, the 2022 mid-term election ballot initiatives and several new research studies. The map has also been updated.

Dr. Tauheed Zaman opens his presentation about marijuana with a photo of Haight-Ashbury street sign, the historic part of San Francisco tied to the hippie and counterculture movements of the 1960s and 1970s, and where the clock is permanently set at 4:20

“It’s just to say that cannabis has really been in our communities and among my patients for a long time,” said Zaman, an addiction psychiatrist at the San Francisco VA Health Care System, during a 2021 virtual presentation hosted by the National Press Foundation for an audience of journalists participating in a fellowship on covering opioids and addiction. “And cannabis has historically also been quite controversial.” 

Marijuana use — and its potency — have only increased since the 1960s, research has shown. 

The percentage of people aged 12 years and older who reported using marijuana during the prior year increased from 11.0%  in 2002 to 17.5%, or 48.2 million people, in 2019, according to the report, “Key Substance Use and Mental Health Indicators in the United States,” published in September 2020 by the federal Substance Abuse and Mental Health Service Administration (SAMHSA). 

Marijuana is the most commonly used illegal drug among people aged 12 years and older, according to the SAMHSA’s  2019 national survey on drug use and health. It is the third most commonly used addictive drug, after tobacco and alcohol, according to the Centers for Disease Control and Prevention. “Illegal” in this case means the drug is not legal on the national level, although that is under consideration.

The House in December 2020 passed the MORE Act of 2020, a bill to decriminalize marijuana. Senate Majority Leader Chuck Shumer said the timeline for the bill is “soon” in an April 2021 interview with Politico.

On Oct. 6, 2022, President Joe Biden pardoned anyone convicted of a federal marijuana possession charge since it became a crime in the 1970s, and urged state governors to do the same for state offenses. He also asked the Secretary of Health and Human Services and the Attorney General to review how marijuana is scheduled under federal law.

As of February 2022, 37 states, District of Columbia, Guam, Puerto Rico and the U.S. Virgin Islands have approved medical marijuana or cannabis laws, according to the National Conference of State Legislatures, which keeps an up-to-date list of laws by state. Many state lawmakers continue to debate on marijuana legalization and decriminalization. NCSL provides an overview of this fast-evolving landscape in the U.S.

Marijuana is legal in 19 U.S. states and the District of Columbia. In the 2022 mid-term election, five more states — Arkansas, Missouri, North Dakota, South Dakota and Maryland — will decide on marijuana legalization, according to Ballotpedia, a nonprofit organization that serves as a digital encyclopedia of American politics.

In Oklahoma, a ballot measure that would have legalized marijuana and decriminalize marijuana possession won’t be on the 2022 ballot after the state’s Supreme Court ruling. State Question 820 will instead appear on a special state election in 2023 or in the 2024 election, according to Oklahoma Watch.

Research on medical benefits, or harm, lags behind the wider availability of cannabis products.

“So these are significant times for cannabis and cannabinoid research policy and health, and it is really important for us to delve into the research and also, as journalists, be able to disseminate what we know and what we don’t know and what the health risks are,” said Ziva Cooper, director of the UCLA Cannabis Research Initiative, during another webinar “Cannabis: Health Effects and Regulatory Issues,” hosted by SciLine in April. SciLine is a free service, connecting scientists with journalists, based at the American Association for the Advancement of Science.

To help journalists add scientific evidence to their stories about marijuana, The Journalist’s Resource has compiled research studies and information shared by experts in two recent virtual events: Zaman’s presentation, “Cannabis Use and Related Disorders,” and SciLine’s “Cannabis: Health Effects and Regulatory Issues” webinar, which included Cooper, Madeline Meier, an associate professor in the department of psychology at Arizona State University and Rosalie Liccardo Pacula, a professor and the Elizabeth Garrett Chair in Health Policy, Economics and Law in the Sol Price School of Public Policy at the University of Southern California.

Quick facts about marijuana — or is it cannabis? 

The cannabis plant has more than 100 known compounds, called cannabinoids. Cannabis plants have small, translucent, hair-like structures called trichomes that store all the cannabinoids. The effect of most of the cannabinoids on human brain and body is still not known. So far, only two cannabinoids have been well studied: tetrahydrocannabinol, or THC, and cannabidiol, or CBD. 

Although “cannabis” and “marijuana” are used interchangeably in everyday dialogue, they’re not quite the same. 

Cannabis is the broader term for all the substances derived from the cannabis plant, some of which could be without THC, including CBD products and terpenes. Meanwhile, marijuana, which is made of the dried leaves, flowers, stems, and seeds and can be smoked or prepared to a concentrated honey-like resin, has THC.  

Cannabis is the more accurate term to use if you’re talking about the industry and products derived from the plant, said Zaman.

Other cannabinoids such as cannabinol, cannabigerol, cannabidivarin are sold at some dispensaries, but have been studied in animals only. There is another set of chemicals in cannabis plants called terpenes, including Myrcene, Pinene, Linalool. They too have only been studied in animals and not humans. 

“There’s much more research to be done,” Zaman said. “Are there many other cannabinoids in there that can have a physiologic effect? Absolutely. I think we’re very early in understanding that.”

Why aren’t the other compounds studied in humans? There are two main barriers. 

First, marijuana is a Schedule I drug under the Federal Comprehensive Drug Abuse Prevention and Control Act of 1970, more commonly known as the Controlled Substances Act. Controlled substances are drugs that have the potential to be misused. They are categorized into five schedules, with Schedule I drugs having the highest potential for abuse.

“So researchers have to deal with a lot more regulation and a lot more barriers to study something that’s scheduled,” said Zaman.

The second barrier is the large number of chemicals in cannabis. 

“It takes a lot of scientific equipment and funding to really isolate each chemical and try to study them individually,” said Zaman. 

Cannabis is prepared in different ways. In addition to smoking it, it can be made into hashish, tinctures, hashish oil and infusions. Table 2 in this 2015 paper in JAMA, “Medical Marijuana for Treatment of Chronic Pain and Other Medical and Psychiatric Problems,” lists the different preparations. 

Cannabis-derived products aren’t to be confused with synthetic cannabinoids, which are sprayed on dried, shredded plant material to make fake marijuana, commonly known as K2 and spice. While synthetic cannabinoids are similar to the chemicals found in the marijuana plant and bind to the same brain receptors, they have a much more powerful effect. 

“Synthetic cannabinoids can lead to cardiac issues, renal issues, psychiatric issues, including psychosis, seizures and death,” said Zaman.

THC content in cannabis plants is increasing

THC is the main known psychoactive compound in the cannabis plants. The THC content of marijuana has increased in recent decades with new growing techniques. The rise has been well-documented and concerns health experts. 

In a November 2020 study, “Changes in Delta‐9‐tetrahydrocannabinol (THC) and Cannabidiol (CBD) Concentrations in Cannabis Over Time: Systematic Review and Meta‐analysis,” published in the journal Addiction, researcher Tom P. Freeman and his colleagues found that the quantity of THC in a typical gram of cannabis rose by 2.9 milligrams each year between 1975 and 2017 for all herbal cannabis, and by 5.7 milligrams each year for cannabis resin, which is a substance produced in the trichomes and can be used to make products like hashish. 

“Changes in THC concentrations over time could also influence the efficacy and safety of cannabis used for medicinal purposes, in the absence of standardized dosing information for illicit cannabis products,” the authors write. 

Meanwhile, the concentration of CBD in cannabis plants has remained the same, the study finds.

So what’s driving this increase? The answer isn’t simple. Pacula explained it this way: The vast majority of the people who consume of most intoxicating goods — whether it’s alcohol, cannabis or even some of the harder substances, is by the near-daily heavy users. They purchase the largest quantity of goods, but represent only about 20% of the total using population. This is known as the 80-20 rule. 

“Because heavy users are the largest purchasers, the industry is inclined to try to sell enticing products to that very small but frequently buying group of users,” said Pacula. “So are they responding to demand? If you’re talking about demand for this very small group of heavy, frequently using cannabis users, the answer is yes. They’re responding to that very small group. But usually when we think about cannabis use, most frequently, what we’re measuring in cannabis use is not those heavy daily users who are using large quantities frequently throughout the day.”

What about medical marijuana? 

“Medical marijuana” is a misnomer, said Zaman. In many instances, there’s little difference between medical marijuana and recreational marijuana.

“States that have legalized cannabis have said, ‘Well, we are calling it medical marijuana or medical cannabis because, under state law, we want to make it legal to get and, therefore, we’re calling it medical,’ but the content, in terms of cannabinoids might be quite similar to recreational marijuana,” said Zaman. 

But even though it’s called medical marijuana and consumers can buy it legally from a dispensary, customers may not be getting exactly what’s listed on the product label. 

In a 2015 study, researchers tested 75 edible marijuana products such as baked goods, beverages, candy or chocolate, purchased from dispensaries in San Francisco, Los Angeles and Seattle and found that only 17% had accurately labeled their THC content. 

“Greater than 50% of products evaluated had significantly less cannabinoid content than labeled, with some products containing negligible amounts of THC. Such products may not produce the desired medical benefit,” wrote lead author Ryan Vandrey in “Cannabinoid Dose and Label Accuracy in Edible Medical Cannabis Products,” published in JAMA

Even though labeling has improved over the years, “There’s still tremendous variability in terms of just THC or CBD content,” said Zaman. “But even if the CBD and THC were accurately labeled, there are so many other compounds in cannabis that are yet to be studied, measured.” 

Cannabis is not federally approved for treatment of any medical conditions 

To date, the federal Food and Drug Administration has not approved cannabis for treatment of any disease or condition. It has, however, approved three products related to or derived from cannabis:

  • Cannabidiol, derived from cannabis and used to treat a rare form of childhood epilepsy. It’s marketed under the name Epidiolex, made by Greenwich Biosciences.
  • Dronabinol, a synthetic cannabinoid marketed under the names Marinol, which was acquired in 2019 by India-based company Alkem Laboratories, although the company’s website doesn’t seem to be available, and Syndros, distributed by Benuvia Therapeutics, and used to treat anorexia and wasting in AIDS patients.
  • Nabilone, a synthetic cannabinoid used for nausea and vomiting in patients undergoing chemotherapy. It’s marketed under the name Cesamet, made by Bausch Health.

These three medications are only available with a prescription. 

Even though cannabis products are touted to help with anxiety and stress, they are not approved by the FDA for any psychiatric conditions. 

In 2013, Zaman did six months of research to help the American Psychiatric Association write a position paper on cannabis use for psychiatric conditions and “all of that work basically boils down to one line, which is there are no current psychiatric indications for which any cannabis product has been proven to be helpful via rigorous scientific studies,” he said.  

That’s not because there have been a lot of negative studies showing that cannabis does absolutely nothing for many psychiatric disorders. But it’s because of the lack of studies, Zaman said.  

The association reviewed its position again in 2018 and still opposes the use of cannabis as a medicine for any psychiatric condition, “because there are so many associations with poorer mental health outcomes in some populations, and not enough studies really showing that there’s a long-term benefit in terms of mental health,” said Zaman. 

The American Society of Addiction Medicine, a professional medical society representing over 6,600 physicians, clinicians and associated professionals in the field of addiction medicine, has a wider ranging set of recommendations for medical professionals who treat addiction. 

Studies of note about health effects of cannabis

A widely cited and comprehensive report by the National Academies of Sciences, Engineering, and Medicine, a private, nonprofit organization, provides a rigorous review of research published between 1999 and 2017 on the health impacts of cannabis and cannabis-derived products, ranging from their therapeutic effects to their risks for causing certain cancers, diseases, mental health disorders and injuries. 

For instance, the report found evidence that patients who were treated with cannabis or cannabinoids were more likely to experience a notable reduction in pain symptoms. But it also found evidence that smoking cannabis on a regular basis is associated with more frequent episodes of chronic bronchitis episodes and worse respiratory symptoms. 

Most studies involving cannabis show an association between the substance and certain changes in the body, but are not able to show cannabis actually causes those changes.   Researchers, however, have established that cannabis does affect psychosis — auditory and visual hallucinations, paranoia and, for some people, disorganized thinking.

More than a decade ago, in a 2007 systemic review of 35 studies, researchers concluded that there was enough evidence “to warn young people that using cannabis could increase their risk of developing a psychotic illness later in life.”

In people who have a family history of schizophrenia or another psychotic illness. Several days of heavy dose use can be enough to develop psychosis in this population, Zaman said.

“So in patients who have a history of psychosis, either personally, or who have it in their families, I absolutely feel I have an obligation to share this information with them,” he said.  

In the May 2021 study, “Relationship Between Cannabis Use and Psychotic Experiences in College Students,” published in the journal Schizophrenia Research, researcher Abigail C. Wright examines the association between cannabis use and hallucinations and delusions in more than 1,034 students at Boston-area colleges between 2010 and 2017. 

They learned that “College students who reported more frequent cannabis use in the past week reported higher levels of hallucinations and delusional ideation. Moreover, those who reported using cannabis more frequently had more distressing delusional ideas, which were held with more conviction.” 

Cannabis use also is associated with preterm birth and low birth weight. 

A study of 5 million live births in California between 2001 and 2012 shows that babies whose mothers had been diagnosed with cannabis use disorder were more likely to be born prematurely and have low birth weights, compared with babies whose mothers didn’t use cannabis. 

“The most notable observation is that exposed infants were 35% more likely to die within 1 year of birth than unexposed infants,” write researchers Yuyan Shi, Bin Zhu and Di Liang in “The Associations Between Prenatal Cannabis Use Disorder and Neonatal Outcomes,” published in April 2021 in the journal Addiction

Researchers say their findings call for prenatal cannabis use disorder prevention, treatment and policies. 

“The American College of Obstetricians and Gynecologists committee has recommended that physicians encourage pregnant women to discontinue cannabis use including medical use,” the authors write. 

What about the association between long-term cannabis use and other physical conditions? 

A 2016 study looks at the number of physical health problems as a function of the duration of cannabis use. It finds that cannabis use over a long period — up to 20 years — was associated with periodontal disease but no other physical health problems by age 38. 

Marijuana use at an early age could have negative long-term effects

Research indicates that when people start using marijuana in adolescence, they are more likely to become addicted to it. 

The brain matures from back to front. People’s frontal lobes, which are associated with thinking, executive function, cognition and impulse control, aren’t fully developed until age 26, which means they remain vulnerable during adolescence. 

“We want to protect the brain as long as we possibly can from the influence of substances, including cannabis, alcohol, opioids, because we want these frontal lobes to have a chance to myelinate and develop properly,” said Zaman. 

In “Young Adult Sequelae of Adolescent Cannabis Use: An Integrative Analysis,” published in Lancet Psychiatry in 2014, Dr. Edmund Silins and his colleagues looked at the association between frequency of cannabis use before age 17 and outcomes such as high school completion, cannabis use disorder and depression among more than 2,500 participants in Australia and New Zealand. 

They learned that people who began using higher doses of cannabis at a younger age were less likely to graduate high school, go to college, attempt suicide and develop an addiction to cannabis and other illicit drugs.

“Prevention or delay of cannabis use in adolescence is likely to have broad health and social benefits,” the authors write. “Efforts to reform cannabis legislation should be carefully assessed to ensure they reduce adolescent cannabis use and prevent potentially adverse developmental effects.”

In a 2012 study, Meier and colleagues look at how IQ is affected by persistent cannabis use. They assessed people’s IQ in childhood, before any of the study participants began using cannabis, and then again in adulthood, after some used cannabis for many years.

“As these adolescent users continued to use for more and more years, they showed more and more IQ decline,” said Meier. “The long-term, persistent, adolescent-onset users lost about eight IQ points from childhood to adulthood.”

Can people get addicted to marijuana?

The simple answer is yes. About one in 10 marijuana users become addicted, according to the CDC

“When you look at people who start in adolescence — again, early on, before that brain development has finished — the rate [of addiction] goes up to 17% at some point in their lives,” said Zaman. “Amongst daily users, 25% to 50% develop a use disorder at some point in their lives, depending on the study that you look at.”

People can also experience marijuana withdrawal. 

“I’ve had many patients go through marijuana withdrawal, particularly when they get admitted to the hospital or travel and suddenly don’t have access to their usual cannabis products,” said Zaman. 

Symptoms of withdrawal include irritability, anger, aggression, anxiety, sleep issues, appetite issues, restlessness, depressed mood and at least one physical symptom such as abdominal pain, shakiness, tremors, sweating, fevers, chills or headaches.


Pacula pointed out that U.S. states have treated cannabis as more of a commercial enterprise because there’s still a lack of clear science that shows it’s a dangerous substance. As a result, many of the regulations tend to focus on licensing, dispensary locations, hours of operation at the local level or laws that allow on-site consumption.

“Testing [of the products] is done, but it’s largely for mold and pesticides,” Pacula said. “And taxation has largely been based on the sale of volume of the good instead of on the major ingredients within the cannabis plant.”

She said five key public health regulations are missing: restrictions on ingredients and extractions allowed from the cannabis plant; restrictions on the amount that can be sold; collecting taxes based on the potency of cannabis instead of the amount sold; compliance checks; and regulation of advertising and the promotion of cannabis products. 

“These are all things that we pay careful attention to when we’re talking about tobacco and alcohol in our state regulations and are things that are often not as carefully addressed in cannabis regulations, thus far,” said Pacula.

Pacula and her colleagues showed in a May 2021 study published in the American Journal of Preventive Medicine that all U.S. states that have legalized marijuana allow a large number of THC doses per transaction — larger than what daily consumers typically use in a month.

“States concerned about public health and diversion should consider reducing sales limits and basing them on total tetrahydrocannabinol content across all purchased products,” the authors write in “Current U.S. State Cannabis Sales Limits Allow Large Doses for Use or Diversion.” 

7 tips for journalists 

1. Take caution when reporting on animal studies. Findings from animal studies usually don’t bear out in humans. “I think it’s really important to keep the community and the U.S. population informed of the fact that what’s happening in a petri dish is very different than what we expect to happen in a human,” said Cooper. 

2. When citing academic studies in online news articles, include a hyperlink. “I really appreciate it when the reporters directly link … to the actual paper,” said Cooper. “So frequently, this does not happen. And it’s really upsetting, especially if somebody is a researcher who wants to go look at the original paper.”

3. When comparing studies, pay attention to differences in study design and the products used. “It’s really important that, as a reporter, you take a look at the [academic] article and see how the paper has defined ‘frequent’ or ‘regular’ or ‘heavy’ cannabis use,” said Meier. “Because lots of times, we’ll see that in one study, we’re talking about 30 or more lifetime uses, and in another study, we’re talking about daily use for 20 years. You can’t compare those two studies.”

Look at whether and how well the authors address alternate explanations for their findings, she added.

Journalists also should take note of which cannabis products are studied “so that we have a sense of how much potency was involved in those products,” said Pacula. “Daily use of a low-potency product is not likely to have any negative, harmful consequences in terms of psychoactive effects and may be very therapeutic and beneficial. Daily use of a concentrate that has an average potency of 70% THC is a different thing.” 

4. Look at how your state regulates alcohol and look for parallels in cannabis regulations. “We have a large number of regulations in place for alcohol that target the at-risk and heavy drinkers. We do not have the same cautions developed in our states or current discussions for national legalization [of marijuana] to protect the typical consumer from becoming a heavy user,” said Pacula. 

5. Don’t use the terms “abuse” or “dependence” when reporting on addiction. Instead, use the phrase “use disorder.” Addiction medicine specialists stopped using the terms “abuse” and “dependence” for two reasons, said Zaman. First, they realized that there was a lot of overlap between patients who were diagnosed with abuse versus dependence. Second, there was stigma attached to those labels. So the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition, or DSM-5 — a manual of all psychiatric diagnoses — uses the term “use disorder.” The severity of the diagnoses is then qualified as mild, moderate or severe. 

What about “addiction”? Zaman said it’s acceptable to use in news reports, even though it’s a colloquial term and not a medical diagnosis. And it’s a broader term, because people can be addicted to more than just substances, including gambling, internet gaming, etc.

The AP stylebook says that “addiction” is a preferred term and “substance use disorder” can be used in quotations or scientific context. It advises against using the terms “abuse” or “problem” and favors the term “use.” Avoid the terms “addict,” “user,” and “abuser.”

6. Be aware of your own biases and leave them out of your marijuana coverage. “Some people may know someone who is using [cannabis] to good effects. Others may have known someone who used it to bad effect or had other personal experiences,” said Zaman. “But I think we need to step back and look at the data, like really dispassionately look at the data. And I think that is kind of what’s missing during some heated discussions around cannabis.”

7. Stress the scientific evidence. “Regardless of whether we’re progressive or liberal or conservative, or whatever part of the spectrum, people should go by the scientific evidence,” said Zaman. “I think the issue is getting politicized and sometimes distracting  from the evidence. What about kids getting ahold of these products? What about adults who have addictions or have psychosis or mental health issues? All of that is being completely glossed over by a belief that A. — this is progressive politics and you better get on this side if you’re progressive — and B. — dollars, dollars, dollars, by which I mean the tax revenue and other financial aspects of the cannabis industry.”

More research studies

Association of Racial Disparity of Cannabis Possession Arrests Among Adults and Youths With Statewide Cannabis Decriminalization and Legalization,” by Brynn E. Sheehan, Richard A. Grucza, Andrew D. Plunk, published in JAMA Health Forum in October 2021, uses arrest data from 43 states to compare “preimplementation and postimplementation differences in arrest rates for states with decriminalization, legalization, and no policy changes.” The study finds that overall, states that legalized or decriminalized cannabis saw large decreases in arrests compared with states that had no policy reform. “Because arrest rate reductions were occurring before policy changes in those states, there is no reason to expect cannabis legalization to have as large of an immediate effect in other states. While these results do not unambiguously favor decriminalization nor legalization, increases in arrest rate disparities in states without either policy highlight the need for targeted interventions to address racial injustice,” the authors write.

The effect of medical cannabis on cognitive functions: a systematic review,” by Anders Wieghorst, Kirsten Kaya Roessler, Oliver Hendricks, and Tonny Elmose Andersen, published in Systematic Reviews in October 2022, is based on the review of 23 studies and finds “the majority of high-quality evidence points in the direction that the negative impact of cannabis-based medicines on cognitive functioning is minor, provided that the doses of THC are low to moderate.” However, longterm use of cannabis-based medicines may see have a negative effect on cognitive functioning, the authors write.

Cannabis Use Patterns and Related Health Outcomes Among Spanish Speakers in the United States and Internationally,” by Renée Martin-Willett, Elizabeth Zambrano Garza, and L. Cinnamon Bidwella, published in the Yale Journal of Biology and Medicine in September 2022, is based on the survey of 549 Spanish-speaking people. Among them, 294 lived in the U.S., 174 lived abroad and others didn’t report the country of residence. Overall, the majority used marijuana for recreational reasons. But the U.S. group was significantly more likely to use marijuana for recreational and/or medical reasons. This group also smoked or vaporized marijuana significantly more often than those living outside of the U.S. or with an undisclosed location, and was more likely to use it daily. About 14% of all survey respondents said they used medical marijuana for anxiety and depression. The study “reveals that Spanish-speaking communities in the U.S. and internationally have both shared and divergent cannabis use patterns, particularly for smoking or vaporizing, medical use, and perceptions of safety or risks of using cannabis,” the authors write.

Watch the presentations and get the handouts

Source list for this piece

Dr. Tauheed Zaman: assistant professor of psychiatry at UCSF’s Weill Institute for Neurosciences and an addiction psychiatrist at the San Francisco VA Health Care System.

Ziva Cooper, Ph.D.: pharmacologist, director of the UCLA Cannabis Research Initiative and an associate professor in UCLA’s departments of psychiatry and anesthesiology.

Madeline Meier, Ph.D.: associate professor in the department of psychology at Arizona State University and the director of and principal investigator at the Substance Use, Health and Behavior Lab at the university.

Rosalie Liccardo Pacula, Ph.D.: professor and the Elizabeth Garrett Chair in Health Policy, Economics & Law at the University of Southern California’s Sol Price School of Public Policy.

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