There is not enough research to reach conclusive judgements on whether marijuana can effectively treat most of the symptoms and diseases it is advertised as helping, according to a wide-ranging US National Academys of Sciences Engineering and Medicine evalutation, which found that the same is also true of many of the claimed risks.
More than 100 conclusions about the health effects of marijuana, including claims of both helpful and harmful effects, were evaluated by the National Academys of Sciences Engineering and Medicine in a new study. The report says there was only enough evidence to support treatment for three therapeutic uses, the study found: to reduce nausea and vomiting from chemotherapy, to treat chronic pain and to reduce spasms from multiple sclerosis.
“Really, most of the therapeutic reasons people use medical marijuana aren’t substantiated beneficial effects of the plant,” said Sean Hennessy, a professor of epidemiology at the University of Pennsylvania, and a member of the 16-scientist committee that carried out the review.
Uses for which there was either “limited evidence or insufficient evidence”, according to Hennessy, included increasing appetite and weight gain for patients with HIV/Aids, calming attention deficit hyperactivity disorder (ADHD) in children, and treating epilepsy.
“There’s been an explosion of literature since 1999 … We reviewed thousands of abstracts,” said Robert Wallace, a professor of epidemiology at the University of Iowa College of Public Health, and another member of the committee tasked with reviewing more than 10,000 studies to reach conclusions about the current state of research on marijuana. “A lot of the report is really where the state of the evidence is.”
For example, the report found “conclusive” evidence that cannabis can alleviate some nausea and vomiting associated with cancer treatment, but that case was long ago considered settled. For many indications in the report, science has not reached a definitive answer.
The study’s key findings fell into a few broad categories:
Injury and death: Evidence suggests that driving while high increases the risk of a car accident. In states where marijuana has been legalised, evidence suggests that children are at more risk of ingesting marijuana. Cannabis use could also harm adolescents’ educational and social development.
Mental health: Cannabis use is likely to increase the risk of developing schizophrenia, social anxiety disorders and, to a lesser extent, depression. Heavy marijuana users are more likely to report suicidal thoughts that non-users, and people with bipolar disorder who use marijuana almost daily show more symptoms than non-users.
Cancer: Evidence does not support a link between smoking marijuana and cancers typically associated with tobacco, such as head, neck and lung cancer. Evidence suggests that smoking marijuana on a regular basis is associated with chronic bronchitis and phlegm production.
Addiction: Evidence suggests that people who use more cannabis are more likely to be addicted, and that the younger people start, the more likely they are to develop problematic use.
Nausea: There is conclusive evidence that cannabinoids, compounds derived from marijuana, are useful to treat nausea and vomiting associated with chemotherapy.
Chronic pain: There is evidence to support use of cannabis in treatment of chronic pain, in particular in spasms associated with multiple sclerosis, the disabling central nervous system disease.
The report says the study comes as the pace of marijuana reforms has quickened across the US. Medicinal marijuana is now legal in 29 states, and recreational marijuana is legal in eight states and in Washington DC.
The report says drug policy reform has also became a topic of international debate, as high-profile medical organisations and some countries call for decriminalisation of illicit drugs. The academies’ report is the first in 18 years to address such a breadth of physical effects from marijuana, and is likely to fuel arguments on both sides of the marijuana debate.
But while the paper is broad and wide-ranging, it is unlikely to end debate on any number of treatments, the report says. One researcher studying the therapeutic impacts of the cannabis compound cannabidiol on children with epilepsy said researchers’ conclusions were broadly “conservative”, and on epilepsy “wrong”.
“For science to do what it does, I think when they do a scientific review they should incorporate all the evidence that is out there for that disorder, and I don’t think they did that for epilepsy,” said Orrin Devinsky, director of New York University Langone Medical Centre’s comprehensive epilepsy centre. Still, he called the research “very valuable”.
The study comes at a significant time for marijuana policy worldwide, as drug policy reform has picked up both in the US and internationally.
The study represents the broadest review by the National Academies of Sciences since 1999, after California and Arizona passed the first medical marijuana laws, and the public debated whether physicians should prescribe marijuana. Controversially, the 1999 report found that marijuana could indeed reduce nausea, but that it could also help treat pain. While the report found some negative effects from smoking marijuana, it also contradicted the then US “drug czar” Barry R McCaffrey’s position that “not a shred of scientific evidence” existed for the medicinal use of marijuana.
The report says almost two decades later, legal marijuana has spawned an untold number of shops hawking marijuana for people to enjoy like beer or wine, but also products that more closely resemble cure-alls on the untested supplement market.
“There is a great fear that I continue to have, that the cannabis industry medically will be like the vitamin and nutritional supplement market,” Devinsky said. “People advertise on TV that we isolated a compound from jellyfish and it improves memory.” He added: “It’s become a religion for people, and my personal view is if you want to pray to whatever gods you pray to, and you want to advocate for whatever political candidate, it’s a free country. But when it comes to medical therapy, we have a higher standard.”
“This growing acceptance, accessibility and use of cannabis and its derivatives has raised important public health concerns,” Marie McCormick, a paediatrician at Harvard University’s TH Chan School of Public Health, who chaired the committee is quoted in the report as saying. “Moreover, the lack of any aggregated knowledge of cannabis-related health effects has led to uncertainty about what, if any, are the harms or benefits from its use.
“We conducted an in-depth and broad review of the most recent research to establish firmly what the science says, and to highlight areas that still need further examination. As laws and policies continue to change, research must also.”
The report also took the unusual step of calling for private funding sources to advance marijuana research. Researchers found it “difficult to gain access to the quantity, quality, and type of cannabis product necessary”, the report said. “A diverse network of funders is needed to support cannabis and cannabinoid research.”
“Any federal study has challenges,” said Nolan Kane, a geneticist at the University of Colorado at Boulder studying the evolution of plants such as sunflowers and hemp. He described government-approved marijuana as having “a fraction” of the psychoactive ingredients of privately grown marijuana, and said research subjects described the marijuana as “old” and “low quality”.
The report is the product of 16 experts in their fields, including neurologists, oncologists, epidemiologists and child psychiatrists. Among the review’s most fervent calls were for more investigation.
The study was sponsored by a group of state health departments, federal agencies and non-profits, such as the Centres for Disease Control and Prevention, the National Highway Traffic Safety Administration, the Robert W Woodruff Foundation and the Arizona department of health services.