(CNN) — Are you using — or considering using — marijuana to help with anxiety, pain, muscle spasms, nausea during pregnancy, poor sleep and more? You may be surprised to discover there is little quality evidence on the benefits of marijuana, according to a new analysis of more than 100 clinical trials and meta-analyses.
“After applying very strict quantitative criteria, and accounting for both observational studies and experimental trials, most of the associations between cannabis and health outcomes were supported by very low or low credibility,” said study author Dr. Marco Solmi, associate professor of psychiatry at the University of Ottawa and investigator at Ottawa Hospital Research Institute in Canada.
Much of the most convincing evidence in the study, in fact, pointed to the potential harms of using marijuana, especially for pregnant women, anyone with a mental health disorder and the adolescents and young adults who currently make up the majority of cannabis users.
“The most concerning findings are the multidimensional detrimental effects of cannabis on brain function, as reflected by associations with poor cognition (and) mental disorders,” Solmi said.
“If we pair these findings with the fact that almost 2/3 of those with mental disorders have onset before age 25, it sounds reasonable to state that cannabis should be avoided in younger strata of the population,” he said.
The review did find some benefits of cannabis use, particularly with “seizure reduction, chronic pain, and muscle spasms,” said Carol Boyd, founding director of the Center for the Study of Drugs, Alcohol, Smoking & Health at the University of Michigan in Ann Arbor, who was not involved with the study.
However, most studies on seizures, nausea and pain have investigated the impact of carefully made synthetic cannabis or extracts, said clinical pharmacologist Robert Page II, who chaired the medical writing group for the American Heart Association’s 2020 scientific statement on marijuana. Page was also not involved in the study.
Such lab-made cannabis-based drugs have extremely high standards, and may even by regulated by the US Food and Drug Administration, which is not the case with most products members of the public can buy at their local cannabis dispensary, Page said.
“So, from a public health standpoint, I don’t want individuals to read this and say, ‘Oh, I can go down to my dispensary and take care of my pain.’ The answer is no, because the products patients are using in the real world are seldom being evaluated in these studies.”
Where marijuana may harm
Mental health: When it comes to easing the symptoms of anxiety, depression and other mental disorders, the analysis found no benefit. In fact, the opposite is actually true, Solmi said.
Mental health can be dramatically impacted by cannabis, the review found. Using the drug raised the risk of an onset of a psychotic or mental health disorder and using it after the onset of a mental condition worsened clinical outcomes, the study found.
“For instance, in people with psychosis, cannabis increases the risk of relapse, and worsens cognition,” Solmi explained.
Psychosis, often defined as emotional upset so severe that a person loses contact with reality, can occur in people with schizophrenia, bipolar disorder or severe depression. It can also be triggered by “sleep deprivation, certain prescription medications, and the misuse of alcohol or drugs,” according to the National Institute of Mental Health.
Pregnancy: Pregnant women too often turn to cannabis to ease their nausea, especially during the first trimester, studies have found. Yet the review found “convincing” evidence for a link between cannabis use and risk of having a small, low birth weight baby.
“Most of the literature on nausea during pregnancy is on prescription-level cannabis, which is synthetically made and carefully controlled as to dose, quality and levels of THC,” Page said.
Delta-9-tetrahydrocannabinol, or THC, is the part of the cannabis plant that produces a “high” — a key reason marijuana helps with nausea and pain, he added.
“It alters perception, which can affect the experience of pain,” Page said. “I do not recommend pregnant women use cannabis because it is linked to low birth weight, and based on animal data, may have effects on the fetal brain. Cannabis can also be passed to the baby while breastfeeding — why take the risk when there are other, safer choices?”
Adolescence and early adulthood: Altering perception and reality while a brain is still developing, as is the case throughout adolescence and a person’s early 20s, is dangerous for cognition and mental health, the review found.
“Adolescents and young adults in particular should be aware that cannabis can have detrimental effects on their mental health, should receive adequate information on effects of cannabis, should not use cannabis, or should monitor their mental health if they decide to use it,” he added.
Beyond psychiatric symptoms, clinical trials have found convincing evidence between cannabis and negative effects on memory, verbal cognition and visual recall, the study said.
“Cannabis worsens multiple domains of cognition,” Solmi said. “Our work can’t answer whether the effects are permanent or not, and more research should be conducted on that topic.”
Young people should “stop using cannabis if they notice a drop in educational achievements, social connections, mental health or functioning in general,” he added.
Where marijuana can help
Areas in which marijuana has been shown to help include seizures disorders, muscle spasms, chronic pain and sleep — but only for certain people, the study found.
“Cannabidiol (CBD) is beneficial for epilepsy, and cannabis-based medicines can improve spasticity in people with multiple sclerosis, pain in chronic pain conditions, (and) sleep in persons suffering from cancer,” Solmi said.
“Overall, cannabis was effective in improving pain across multiple measures of pain across different populations, he said. However, there is “no evidence cannabis improves sleep in the general population.”
And no one suffering from any of these conditions should self-medicate with cannabis, Solmi stressed.
“Those suffering from epilepsy, multiple sclerosis, or chronic pain, should seek medical advice and not self-treat symptoms with cannabis, given that it can be associated with adverse events, as any substance or medication that is commonly prescribed,” Solmi said.
Still, the review found conclusions with high certainty in either direction — positive or negative — were few and far between, said Cinnamon Bidwell, associate professor of psychology and neuroscience at the University of Colorado Boulder, who was not involved in the research.
“This literature has been strongly limited by regulatory barriers that restrict cannabis research,” she said. “The biggest take home from this summary is a need to provide pathways for researchers to conduct many more rigorous and valid trials on the harms and benefits of forms of cannabis accessible on legal markets.”