Whether marijuana helps with pain is unclear

Daily users with severe pain report worsening health

April 8, 2020

Science Daily/Ohio State University

Medical marijuana users who say they have high levels of pain are more likely than those with low pain to say they use cannabis three or more times a day, a new study finds.

However, daily marijuana users with severe pain also reported their health had become worse in the past year.

The results don't necessarily mean that marijuana is not effective in treating at least some kinds of pain, according to the researchers. But it suggests more research is needed before marijuana is accepted as an effective treatment for severe pain.

"It's not clear if marijuana is helping or not," said Bridget Freisthler, co-author of the study and professor of social work at The Ohio State University.

"The benefits aren't as clear-cut as some people assume."

The study was published recently in the International Journal of Drug Policy.

One issue is the complex relationship between pain, marijuana use and self-reported health, said Alexis Cooke, lead author of the study and postdoctoral scholar in psychiatry at the University of California, San Francisco.

"Having high chronic pain is related to poorer health, so it may be that people who are using marijuana more often already had worse health to begin with," Cooke said.

"There are still a lot of questions to answer."

The study involved a survey of 295 medical marijuana dispensary patients in Los Angeles. The surveys were conducted in 2013, when California allowed marijuana use only for medical purposes.

All participants were asked how often they used marijuana; rated how their current health compared to one year ago (on a five-point scale from "much better" to "much worse"); and were asked two questions about their pain levels. Based on their answers, the researchers rated participants' pain as low, moderate or high.

Among those surveyed, 31 percent reported high pain, 24 percent moderate pain, and 44 percent were in the low-pain category.

Daily marijuana use was reported by 45 percent of the sample, and 48 percent said they used three or more times per day.

The percentage of participants who used marijuana every day did not differ by pain categories. But about 60 percent of those who reported high pain used the drug three or more times a day, compared to 51 percent of those with moderate pain and 39 percent of those in the low-pain group.

Findings showed no association between daily marijuana use and change in health status among those with low levels of pain. But daily marijuana use was linked to worsening health status among those reporting high levels of pain.

However, strangely, there was no association between how often participants used marijuana per day and changes in health status. There's no easy explanation for this, Freisthler said.

"It shows how little we know about marijuana as medicine, how people are using it, the dosages they are receiving and its long-term effects," she said.

People use marijuana for a variety of different types of pain, including cancer, joint pain, HIV and nerve pain. Researchers don't know if marijuana has different effects on different causes of pain, Cooke said.

"Chronic pain is also associated with depression and anxiety. Marijuana may help with these problems for some people, even if it doesn't help with the pain," she said.

In addition, marijuana use seems to help people who have lost their appetite due to pain or nausea caused by cancer drugs.

"It may not be the pain that patients are trying to address," Cooke said.

The results do suggest we need to know more about the link between marijuana and pain relief, Freisthler said.

"Particularly since the opioid crisis, some people have been touting marijuana as a good substitute for opioids for people in pain," she said.

"But our study suggests we don't know that marijuana is helping to address pain needs."

https://www.sciencedaily.com/releases/2020/04/200408145805.htm

Focus on opioids and cannabis in chronic pain media coverage

January 17, 2020

Science Daily/University of Otago

New Zealand media reports on chronic pain are focusing on treatments involving opioids and cannabis at the expense of best practice non-drug treatments, researchers have found.

Chronic pain, defined as persistent or recurring pain present for more than three months, is the leading cause of disability worldwide and affects one in five New Zealanders.

The researchers analysed 240 news articles on chronic pain published in the New Zealand news media between January 2015 and June 2019. Their report is published in the latest issue of the New Zealand Medical Journal.

Lead author Dr Hemakumar Devan, a Postdoctoral fellow at the Centre for Health, Activity and Rehabilitation Research at the University of Otago, Wellington's School of Physiotherapy, says few of the news stories included information about non-pharmaceutical treatments for chronic pain, despite these being the preferred option for most chronic pain conditions.

"Pharmacological strategies are only recommended for some chronic pain conditions, such as cancer pain and neuropathic pain. For other pain conditions, drug treatments are recommended to be used with care and caution because of potential side effects and limited long-term effectiveness."

He says media coverage of pharmaceutical treatments for chronic pain focused almost entirely on opioid-based painkillers and cannabis. Stories on opioids mentioned their ineffectiveness in treating chronic pain and their potential for dependence and addiction, while reports about medicinal cannabis portrayed it as an effective and safe treatment with minimal side effects. This was despite the lack of scientific evidence to support its long-term use for chronic pain.

"The personal experience stories about cannabis focused on its positive effects and fewer side effects compared to opioid-based analgesics. There is, however, limited evidence to suggest cannabis as a substitute for opioids and a lack of high-quality evidence to support the use of cannabis for chronic pain.

"There was no reporting on the potential adverse effects of medicinal cannabis use, such as cognitive deficits, dependency and mood changes, which could particularly affect young people."

The researchers also found media coverage was dominated by the struggle associated with living in chronic pain, with little attention given to the resources available to support people to manage pain successfully and live a meaningful life.

"Non-drug based self-management strategies, which include exercise, relaxation and cognitive behavioural treatments, are a key component of managing chronic pain and are proven to be effective in the long term."

Dr Devan says the difficulties faced by patients in accessing pain services because of the lack of trained multidisciplinary health professionals, and inequities in terms of access for Māori and Pasifika, were accurately reflected by the media coverage.

The researchers found the level of media interest in chronic pain had increased in recent years.

"We expect this will continue to rise, with chronic pain becoming increasingly relevant in the lead up to New Zealand's 2020 cannabis referendum; and as the number of people living with chronic pain increases as the population ages."

https://www.sciencedaily.com/releases/2020/01/200117094323.htm

Medical cannabis significantly safer for elderly with chronic pain than Opioids

February 13, 2018

Science Daily/American Associates, Ben-Gurion University of the Negev

A new study found cannabis therapy is safe and efficacious for elderly patients who are seeking to address cancer symptoms, Parkinson's disease, post-traumatic stress disorder, ulcerative colitis, Crohn's disease, multiple sclerosis, and other medical issues. After six months, more than 18 percent of patients surveyed had stopped using opioid analgesics or had reduced their dosage.

Medical cannabis therapy can significantly reduce chronic pain in patients age 65 and older without adverse effects, according to researchers at Ben-Gurion University of the Negev (BGU) and the Cannabis Clinical Research Institute at Soroka University Medical Center.

The new study, published in The European Journal of Internal Medicine, found cannabis therapy is safe and efficacious for elderly patients who are seeking to address cancer symptoms, Parkinson's disease, post-traumatic stress disorder, ulcerative colitis, Crohn's disease, multiple sclerosis, and other medical issues.

"While older patients represent a large and growing population of medical cannabis users, few studies have addressed how it affects this particular group, which also suffers from dementia, frequent falls, mobility problems, and hearing and visual impairments," says Prof. Victor Novack, M.D., a professor of medicine in the BGU Faculty of Health Sciences (FOHS), and head of the Soroka Cannabis Clinical Research Institute. Novack is also the BGU Gussie Krupp Chair in Internal Medicine.

"After monitoring patients 65 and older for six months, we found medical cannabis treatment significantly relieves pain and improves quality of life for seniors with minimal side effects reported."

This older population represents a growing segment of medical cannabis users, ranging from approximately seven percent to more than 33 percent, depending on the country. Recent U.S. polls indicate Americans over 65 represent 14 percent of the total population and use more than 30 percent of all prescription drugs, including highly addictive painkillers.

BGU researchers surveyed 2,736 patients 65 years and older who received medical cannabis through "Tikun Olam," the largest Israeli medical cannabis supplier. More than 60 percent were prescribed medical cannabis due to the pain, particularly pain associated with cancer. After six months of treatment, more than 93 percent of 901 respondents reported their pain dropped from a median of eight to four on a 10-point scale. Close to 60 percent of patients who originally reported "bad" or "very bad" quality of life upgraded to "good" or "very good" after six months. More than 70 percent of patients surveyed reported moderate to significant improvement in their condition.

The most commonly reported adverse effects were dizziness (9.7 percent) and dry mouth (7.1 percent). After six months, more than 18 percent of patients surveyed had stopped using opioid analgesics or had reduced their dosage.

All patients received a prescription after consulting with a doctor who prescribed treatment. More than 33 percent of patients used cannabis-infused oil; approximately 24 percent inhaled therapy by smoking, and approximately six percent used vaporization.

While the researchers state their findings to date indicate cannabis may decrease dependence on prescription medicines, including opioids, more evidence-based data from this special, aging population is imperative.

https://www.sciencedaily.com/releases/2018/02/180213111508.htm

Cannabis: Non-addictive pathway to pain relief?

Medicinal properties of cannabis examined

January 12, 2017

Science Daily/Oregon Health & Science University

OHSU research suggests an avenue for developing treatments for chronic pain that harness the medicinal properties of cannabis while minimizing the threat of addiction.

The study, conducted in a rodent model, provides additional rationale for the development of therapeutics using cannabinoid receptors to treat chronic pain, which afflicts about 30 percent of the U.S. population. OHSU investigators studied the function of two forms of cell membrane receptors that bind cannabinoids that occur naturally within the body, called endocannabinoids.

"It may be an avenue where we can get better pain medications that are not addictive," said senior author Susan Ingram, Ph.D., an associate professor of neurosurgery in the OHSU School of Medicine.

Ingram and colleagues report the treatment of chronic pain has challenged the medical system, with medications that are ineffective or create serious side effects: "However, emerging data indicate that drugs that target the endocannabinoid system might produce analgesia with fewer side effects compared with opioids."

The body's endocannabinoid system comprises receptors, endocannabinoid molecules and enzymes that make and degrade the endocannabinoids located in the brain and throughout the central and peripheral nervous system. The research team focused on two cannabinoid receptors, known as CB1 and CB2, in the rostral ventromedial medulla -- a group of neurons located in the brainstem known to modulate pain. The study is the first to examine CB1 and CB2 receptor function at the membrane level in late adolescent and adult neurons.

The researchers observed that chronic inflammatory pain increased activity of CB2 receptors and decreased CB1 activity. Cannabis activates both CB1 and CB2 receptors equally. The study suggests that selective activation of CB2 receptors contributes to the medicinal benefit of cannabis while minimizing the propensity of the other cannabinoid receptor, CB1, to induce tolerance and withdrawal. Ingram said the next phase of the research will further explore this area of brain circuitry, which ultimately could lead to the development of a new class of pain medications.

Co-authors include lead author Ming-Hua Li, Ph.D., and Katherine L. Suchland, both with the Department of Neurological Surgery, OHSU School of Medicine.

The study was funded by grants from the National Institutes of Health (DA035316 and R56NS093894) and American Heart Association (13SDG14590005, MH.L.).

https://www.sciencedaily.com/releases/2017/01/170112130145.htm

Medical marijuana could help patients reduce pain with opiates

December 6, 2011

Science Daily/University of California - San Francisco

A UCSF study suggests patients with chronic pain may experience greater relief if their doctors add cannabinoids -- the main ingredient in cannabis or medical marijuana -- to an opiates-only treatment. The findings, from a small-scale study, also suggest that a combined therapy could result in reduced opiate dosages.

More than 76 million Americans suffer from chronic pain -- more people than diabetes, heart disease and cancer combined, according to the National Centers for Health Statistics.

"Pain is a big problem in America and chronic pain is a reason many people utilize the health care system," said the paper's lead author, Donald Abrams, MD, professor of clinical medicine at UCSF and chief of the Hematology-Oncology Division at San Francisco General Hospital and Trauma Center (SFGH). "And chronic pain is, unfortunately, one of the problems we're least capable of managing effectively."

In a paper published this month in Clinical Pharmacology & Therapeutics, researchers examined the interaction between cannabinoids and opiates in the first human study of its kind. They found the combination of the two components reduced pain more than using opiates alone, similar to results previously found in animal studies.

Researchers studied chronic pain patients who were being treated with long-acting morphine or long-acting oxycodone. Their treatment was supplemented with controlled amounts of cannabinoids, inhaled through a vaporizer. The original focus was on whether the opiates' effectiveness increased, not on whether the cannabinoids helped reduce pain.

"The goal of the study really was to determine if inhalation of cannabis changed the level of the opiates in the bloodstream," Abrams said. "The way drugs interact, adding cannabis to the chronic dose of opiates could be expected either to increase the plasma level of the opiates or to decrease the plasma level of the opiates or to have no effect. And while we were doing that, we also asked the patients what happened to their pain."

Abrams and his colleagues studied 21 chronic pain patients in the inpatient Clinical and Transitional Science Institute's Clinical Research Center at SFGH: 10 on sustained-release morphine and 11 on oxycodone. After obtaining opiate levels from patients at the start of the study, researchers exposed them to vaporized cannabis for four consecutive days. On the fifth day, they looked again at the level of opiate in the bloodstream. Because the level of morphine was slightly lower in the patients, and the level of oxycodone was virtually unchanged, "one would expect they would have less relief of pain and what we found that was interesting was that instead of having less pain relief, patients had more pain relief," Abrams said. "So that was a little surprising."

The morphine group came in with a pain score of about 35, and on the fifth day, it decreased to 24 -- a 33 percent reduction. The oxycodone group came in with an average pain score of about 44, and it reduced to 34 -- a drop of 20 percent. Overall, patients showed a significant decrease in their pain.

"This preliminary study seems to imply that people may be able to get away perhaps taking lower doses of the opiates for longer periods of time if taken in conjunction with cannabis," Abrams said.

Opiates are very strong powerful pain medicines that can be highly addictive. They also can be deadly since opiates sometimes suppress the respiratory system.

As a cancer doctor, Abrams was motivated to find safe and effective treatments for chronic pain. Patients in the cannabis-opiates study experienced no major side effects such as nausea, vomiting or loss of appetite.

"What we need to do now is look at pain as the primary endpoint of a larger trial," he said. "Particularly I would be interested in looking at the effect of different strains of cannabis."

For instance, Delta 9 THC is the main psychoactive component of cannabis but cannabis contains about 70 other similar compounds with different effects. One of those is cannabidiol, or CBD. It appears to be very effective against pain and inflammation without creating the "high" created by THC.

"I think it would be interesting to do a larger study comparing high THC versus high CBD cannabis strains in association with opiates in patients with chronic pain and perhaps even having a placebo as a control," Abrams said. "That would be the next step."

Abrams is the lead author of the paper; co-authors are Paul Couey, BA, and Mary Ellen Kelly, MPH, of the UCSF Division of Hematology-Oncology at SFGH; Starley Shade, PhD, of the UCSF Center for AIDS Prevention Studies; and Neal Benowitz, MD, of the UCSF Division of Clinical Pharmacology and Experimental Therapeutics.

The study was supported by funds from the National Institutes on Drug Abuse (NIDA), a subsidiary of the National Institutes of Health (NIH).

Major Components of Cannabis

·     Delta-9 Tetrahydrocannabinol (Delta-9 THC)-- It is the main psychoactive component of cannabis with mild to moderate painkilling effects. It also helps treat nausea associate with cancer chemotherapy and to stimulate appetite. It induces feelings of euphoria. Potential side effects include accelerated heartbeat, panic, confusion, anxiety and possible paranoia.

·     Cannabidiol (CBD)- It is a major, non-psychoactive component of cannabis that helps shrink inflammation and reduce pain without inducing the euphoria effects of THC. It has been used to treat rheumatoid arthritis, inflammatory bowel diseases, psychotic disorders and epilepsy. Larger amounts of CBD can relax the mind and body without causing negative side effects associated with THC.

·     Cannabinol (CBN)-- It is a secondary psychoactive component of cannabis. It is not associated with painkilling effects of THC or CBD. CBN is formed as THC ages. Unlike the euphoria effects of THC, CBN can induce headaches and a sense of lethargy.

·     Tetrahydrocannabivarin (THCV) -- It is found primarily in strains of African and Asian cannabis. THCV heightens the intensity of THC effects and the speed in which the component is delivered, but also causes the sense of euphoria to end sooner.

https://www.sciencedaily.com/releases/2011/12/111206151448.htm

Marijuana vaporizer provides same level of THC, fewer toxins

May 16, 2007

Science Daily/University of California - San Francisco

A smokeless cannabis-vaporizing device delivers the same level of active therapeutic chemical and produces the same biological effect as smoking cannabis, but without the harmful toxins, according to University of California San Francisco researchers.

Results of a UCSF study, which focuses on delivery of the active ingredient delta-9-tertrahydrocannibinol, or THC, are reported in the online issue of the journal "Clinical Pharmacology and Therapeutics."

"We showed in a recent paper in the journal 'Neurology' that smoked cannabis can alleviate the chronic pain caused by HIV-related neuropathy, but a concern was expressed that smoking cannabis was not safe. This study demonstrates an alternative method that gives patients the same effects and allows controlled dosing but without inhalation of the toxic products in smoke," said study lead author Donald I. Abrams, MD, UCSF professor of clinical medicine.

The research team looked at the effectiveness of a device that heats cannabis to a temperature between 180 and 200 degrees C, just short of combustion, which occurs at 230 degrees C. Eighteen individuals were enrolled as inpatients for six days under supervision in the General Clinical Research Center at San Francisco General Hospital Medical Center.

Under the study protocol, the participants received on different days three different strengths of cannabis by two delivery methods--smoking or vaporization--three times a day.

Plasma concentrations of THC were measured along with the exhaled levels of carbon monoxide, or CO. A toxic gas, CO served as a marker for the many other combustion-generated toxins inhaled when smoking. The plasma concentrations of THC were comparable at all strengths of cannabis between smoking and vaporization. Smoking increased CO levels as expected, but there was little or no increase in CO levels after inhaling from the vaporizer, according to Abrams.

"Using CO as an indicator, there was virtually no exposure to harmful combustion products using the vaporizing device. Since it replicates smoking's efficiency at producing the desired THC effect using smaller amounts of the active ingredient as opposed to pill forms, this device has great potential for improving the therapeutic utility of THC," said study co-author Neal L. Benowitz, MD, UCSF professor of medicine, psychiatry and biopharmaceutical sciences. He added that pills tend to provide patients with more THC than they need for optimal therapeutic effect and increase side effects.

Patients rated the "high" they experienced from both smoking and vaporization and there was no difference between the two methods by patient self-report of the effect, according to study findings. In addition, patients were asked which method they preferred.

"By a significant majority, patients preferred vaporization to smoking, choosing the route of delivery with the fewest side effects and greatest efficiency," said Benowitz.

Co-authors include Cheryl A. Jay, MD, UCSF neurology; and Starley B. Shade, MPH; Hector Vizoso, RN; and Mary Ellen Kelly, MPH, UCSF Positive Health Program at San Francisco General Hospital Medical Center.

The study was funded by the University of California's Center for Medicinal Cannabis Research.

https://www.sciencedaily.com/releases/2007/05/070515151145.htm

Cannabinoid drugs make pain feel 'less unpleasant, more tolerable'

September 19, 2018

Science Daily/Syracuse University

Researchers in the College of Arts and Sciences have determined that cannabinoid drugs do not appear to reduce the intensity of experimental pain, but, instead, may make pain feel less unpleasant and more tolerable.

Martin De Vita G'17, a doctoral candidate in the clinical psychology program, is the lead author of a highly anticipated paper on the subject in JAMA Psychiatry (American Medical Association, 2018).

The paper, whose publication coincides with "Pain Awareness Month," represents the first systematic review of experimental research into the effects of cannabis on pain.

"Cannabinoid drugs are widely used as analgesics [painkillers], but experimental pain studies have produced mixed findings," says De Vita, who studies interactions between substance use and co-occurring health conditions. "Pain is a complex phenomenon with multiple dimensions that can be affected separately."

Cannabinoids are chemical compounds that give the Cannabis plant its medical and recreational properties. Marijuana -- a mixture of dried, crumbled parts from the plant -- contains hundreds of these compounds, of which Tetrahydrocannabinol, or THC, is the best known.

"THC is the primary psychoactive compound in marijuana and, along with CBD [also known as cannabidiol, a naturally occurring constituent of cannabis] has been the focus of most medicinal use and research," says Associate Professor Emily Ansell, the study's senior author and director of the University's Research Lab on Personality, Addiction and Trauma (REPEAT).

When ingested, THC binds to receptors in the brain that control pleasure, time perception and pain. This activity boasts the production of dopamine -- what Ansell calls the "feel-good chemical," resulting in euphoria or relaxation.

Although the use of cannabis for medical purposes is legal in more than 30 states, the U.S. Drug Enforcement Administration still considers it a Schedule I drug, with no accepted medical use and a high potential for abuse. This classification, De Vita says, poses a significant challenge to researchers interested in cannabis' therapeutic effects.

Thus, high-quality evidence supporting the effectiveness of cannabis in treating chronic pain has yet to be established.

"Patients reliably endorse the belief that cannabis is helpful in alleviating pain; however, its analgesic properties are poorly understood," says De Vita, also a student therapist in the Syracuse VA Medical Center's PTSD clinic and a graduate researcher in the University's REPEAT Lab and Alcohol Research Lab. "Experimental pain studies of cannabinoid analgesia in healthy adults have produced mixed results."

De Vita and his co-authors in the Department of Psychology -- doctoral candidate Dezarie Moskal, Professor Stephen Maisto and Ansell -- initially identified more than 1,830 experimental studies on cannabis that had been conducted in North America and Europe over a 40-year period. They whittled the group down to 18 studies, and extracted data from more than 440 adult participants.

The team found that cannabinoid drugs were associated with modest increases in experimental pain threshold and tolerance, no reduction in the intensity of ongoing experimental pain, reduced perceived unpleasantness of painful stimuli and no reduction of mechanical hyperalgesia.

"What this means is that cannabinoid analgesia may be driven by an affective, rather than a sensory component. These findings have implications for understanding the analgesic properties of cannabinoids," De Vita says.

Adds Ansell: "The studies predominantly focused on THC varieties, so it is unclear whether or not other cannabinoids may have resulted in different experimental effects on pain."

The first meta-analytic review of its kind, Syracuse's study closely followed published guidelines for conducting and reporting systematic reviews, as well as a pre-registered protocol to enhance transparency. Two independent reviewers also examined the data separately.

"The mean quality and validity score across the studies was high, and analyses did not suggest publication bias," De Vita says.

Whereas the study was limited to experimental (i.e., laboratory induced) pain, the group hopes to expand their line of research into clinical and neuropathic pain.

Clinical pain usually is associated with a progressive, non-malignant disease; neuropathic pain is synonymous with disease or damage to the nervous system, resulting in tissue injury.

The researchers also are interested in studying dynamic pain processes, different types and doses of cannabinoids, and the role of recreational cannabis use.

"The cumulative research synthesized in our review has helped characterize how cannabis and cannabinoids affect different dimensions of pain reactivity," De Vita adds. "It may underlie the widely held belief that cannabis relieves pain. For now, we still have much to learn."

https://www.sciencedaily.com/releases/2018/09/180919111454.htm

Cannabis: A new frontier in therapeutics

February 15, 2015

Science Daily/McGill University Health Centre

While debate about recreational marijuana use continues, researchers are investigating the effectiveness of cannabis for treating pain, spasticity, and a host of other medical problems. In a symposium organized by the McGill University Health Centre (MUHC) as part of the 2015 American Association for the Advancement of Science Annual Meeting held this week in San Jose, California, experts from North America and the U.K. share their perspectives on the therapeutic potential of medical cannabis and explore the emerging science behind it.

"We need to advance our understanding of the role of cannabinoids in health and disease through research and education for patients, physicians and policy-makers," says Dr. Mark Ware, director of clinical research at the Alan Edwards Pain Management Unit at the MUHC, in Canada.

As a pain specialist Dr. Ware regularly sees patients with severe chronic pain at his clinic in Montreal, and for some of them, marijuana appears to be a credible option. "I don't think that every physician should prescribe medical cannabis, or that every patient can benefit but it's time to enhance our scientific knowledge base and have informed discussions with patients."

Increasing numbers of jurisdictions worldwide are allowing access to herbal cannabis, and a range of policy initiatives are emerging to regulate its production, distribution, and authorization. It is widely believed that there is little evidence to support the consideration of cannabis as a therapeutic agent. However, several medicines based on tetrahydrocannabinol (THC), the psychoactive ingredient of cannabis, have been approved as pharmaceutical drugs.

Leading British cannabis researcher Professor Roger Pertwee, who co-discovered the presence of tetrahydrocannabivarin (THCV) in cannabis in the 70's, recently published with collaborators some findings of potential therapeutic relevance in the British Journal of Pharmacology. "We observed that THCV, the non-psychoactive component of cannabis, produces anti-schizophrenic effects in a preclinical model of schizophrenia," says Pertwee, professor of Neuropharmacology at Aberdeen University. "This finding has revealed a new potential therapeutic use for this compound."

Neuropsychiatrist and Director of the Center for Medicinal Cannabis Research (CMCR) at the University of California, San Diego Dr. Igor Grant is interested in the short and long-term neuropsychiatric effects of marijuana use. The CMCR has overseen some of the most extensive research on the therapeutic effects of medical marijuana in the U.S. "Despite a commonly held view that cannabis use results in brain damage, meta analyses of extensive neurocognitive studies fail to demonstrate meaningful cognitive declines among recreational users," says Dr. Grant. "Bain imaging has produced variable results, with the best designed studies showing null findings."

Dr. Grant adds that while it is plausible to hypothesize that cannabis exposure in children and adolescents could impair brain development or predispose to mental illness, data from properly designed prospective studies is lacking.

https://www.sciencedaily.com/releases/2015/02/150215070209.htm