With voters in several states asked to decide about recreational and medical marijuana, a quick look at the state of knowledge about the drug and its derivatives
Voters will go to the polls Tuesday to determine whether several states will legalize marijuana for medical or recreational uses, even as the federal government maintains it is an illegal drug to possess, grow, buy or sell.
That federal status makes it hard to study marijuana's effects directly, through clinical trials and other kinds of research.
But several University of Michigan researchers have studied the effects of marijuana, also called cannabis, and looked at evidence from other researchers.
Here's what they say:
Impacts on the brain: Meghan Martz, Ph.D.
Martz, a research psychologist in the U-M Addiction Center and Department of Psychiatry, and former research team member at the U-M Institute for Social Research, looks at the impact of long-term marijuana use on the brain, and patterns of marijuana use on populations.
She was first author of a 2016 paper in JAMA that found that those who had used marijuana for a while had a dampened response to rewards, when researchers looked at their brains in MRI scanners.
"Research findings indicate that early substance use has detrimental effects on the brain, so early adolescent marijuana use is generally thought of as more problematic than adult use in terms of negative outcomes. But certain areas of the brain may be more sensitive to drug use even through early adulthood.
For example, the brain's prefrontal cortex, which is involved in impulse control and decision making, continues to mature though the mid-20s. Marijuana can also impact other brain regions, such as those associated with reward responsivity and emotional processing.
Our research lab here at Michigan, led by Mary Heitzeg, Ph.D., has found that marijuana use in the early twenties may contribute to decreased brain activation during the anticipation of non-drug rewards. Our interpretation of these results is that natural rewards may be dampened in marijuana users, which may increase risk for addiction to marijuana.
In another study from our lab, we found that marijuana use in adolescence may have downstream effects on emotional functioning in the early twenties.
It is possible that low levels of marijuana use may be less concerning in relation to effects on the adolescent and young adult brain, but we do not yet really know what "safe" levels are and how those thresholds may vary by age. In our work, we're most often concerned with developmental trajectories of heavy use over time.
The Adolescent Brain Cognitive Development (ABCD) Study, which has a site here at Michigan, is a multi-site, 10-year longitudinal study that, along with other areas of interest on adolescent health and well-being, seeks to answer questions pertaining to factors that contribute to risk for developing substance use problems and the effects of continued drug use over time on the brain. The ABCD Study just began, so it will be interesting to see results over time. This is the first large-scale study to examine predictors and outcomes of substance use using both neural and psychosocial measures in a nationally representative sample of youth."
A Pain Expert's View: Daniel Clauw, M.D.
Clauw, who specializes in treating fibromyalgia and other chronic pain disorders, worked with colleague Kevin Boehnke, Ph.D., to study cannabis' impact on chronic pain among 244 Michigan medical marijuana users; their results were published in 2016.
He notes that medical marijuana advocates have used scientific data and compelling patient stories to show the impact of substances derived from marijuana, called cannabinoids.
But the evidence on using marijuana or cannabinoids to treat non-cancer chronic pain is far from perfect, he says.
He points to a recent new analysis of data from 104 studies on cannabis and cannabis-derived substances for treatment of chronic-non-cancer pain. They find that many of the studies of cannabis and its derivatives were too small, and too short, to make definitive answers possible – and that they didn't record the cannabis doses well, and didn't consider the longer-term implications of cannabis use.
The authors, and Clauw, called for well-conducted, large randomized controlled trials with at least 100 participants receiving the cannabis-derived chemical, and 100 participants receiving some other treatment.
"Marijuana legalization advocates have especially focused on conditions such as chronic pain, epilepsy and post-traumatic stress disorder, which are notoriously difficult to treat with standard therapies.
Although the lay public has moved rapidly toward accepting cannabis decriminalization or legalization, the medical community does not generally share this enthusiasm for cannabinoids. Notwithstanding the legal issues (cannabis is still a Schedule I drug that cannot be prescribed), there are other legitimate issues that preclude acceptance by physicians. Even if we could prescribe cannabis, we have no idea what strength or dose to use, or which route of administration is most effective.
Cannabis should generally be used after more established therapies (both drug and non-drug) have failed. In this regard, using this therapy should be considered a bit like opioids should have been – after most other things have failed. However, it's important to note that those risks are not nearly as bad as opioids – for instance, you cannot die of a cannabis overdose, and it's less addictive -- but cannabinoid has very little risk or potential for harm we are aware of.
People should try cannabidiol (CBD) alone and only if that doesn't work add a bit of THC. Instead of using CBD or high CBD-low THC strains people are typically using far too much THC, and often getting high instead of getting good pain relief. The THC is also where all of the "risks" are.
A public poll leader's view: Preeti Malani, M.D.
As a trained specialist in treating older adults, Malani is interested in finding out their thoughts about health-related issues on a national scale, to help inform what health providers and policymakers do. She leads the National Poll on Healthy Aging, funded by U-M and AARP, which conducts rigorously designed polls of adults over age 50 and publishes reports about the findings.
Earlier this year, the poll issued results from questions about marijuana-related issues, asked of more than 2,000 people ages 50 to 80 in October 2017.
Malani describes the key findings:
We found that four out five of poll respondents support allowing medical marijuana if it's recommended by a physician, and two out of five support allowing marijuana use for any reason.
Two-thirds say the government should do more to study the drug's health effects, which is very difficult to do directly under current law.
While just six percent of our poll respondents said they'd used marijuana for medical purposes themselves, 18 percent said they know someone who has. With medical marijuana already legal in 29 states and the District of Columbia, and other states considering legalizing this use or all use, this is an issue of interest to patients, providers and policymakers alike.
I think our findings show that older Americans have a sense of wariness, rather than wholehearted acceptance, around medical use of marijuana. This may be surprising to those who think of the Baby Boom generation - who are now in their mid-50s to early 70s - as embracing marijuana use in their youth in the 1960s and 1970s.
Just under one-third of respondents said they feel that marijuana definitely provides pain relief, and another 38 percent said it probably does. But only 14 percent thought marijuana was more effective than prescription pain medication, while 48 percent believed the opposite and 38 percent believed the two were equally effective.
We asked about negative effects of marijuana and prescription pain medicines. Nearly half thought the prescription drugs are more addictive than marijuana, and more than half said that such medicines have more side effects than marijuana.
These perceptions of relative safety and efficacy are important for physicians, other providers and public health regulators to understand, since marijuana use, particularly long-term use, has been associated with impaired memory, decision making and ability to perform complex tasks.
A long-term youth study's view:
For more than 40 years, a team from the U-M Institute for Social Research has fanned out to high schools, college campuses and the community, to ask teens and young adults about their use of substances ranging from tobacco and alcohol to marijuana, opioids, methamphetamine and cocaine.
Called the Monitoring the Future Study, it's considered a gold standard for understanding young people's attitudes and practices regarding these substances.
In September, the study's leaders published a review of trends they've seen over those 40 years. One of their key findings: that marijuana use is now at the highest level in 30 years among people ages 19 to 22, whether or not they are in college.
In all, the researchers say, 38 percent of full-time college students aged 19-22 reported using marijuana at least once in the prior 12 months, and 21 percent reported using at least once in the prior 30 days.
Among those not in college, or not attending college full-time, 41 percent had used it in the past year, and 28 percent had used it in the past 30 days. And more than 13 percent of these young people used marijuana daily – a doubling in the past decade, and a contrast with full-time students, whose daily use was around 4 percent.
While these levels are lower than what the researchers saw in the early 1980s when they started surveying post-high-school young people, the researchers note that only 27 percent of today's 19- to 22-year-olds say they think marijuana is harmful.
"The continued increase of daily marijuana use among non-college youth is especially worrisome," said John Schulenberg, principal investigator of the Monitoring the Future Panel Study. "The brain is still growing in the early 20s, and the scientific evidence indicates that heavy marijuana use can be detrimental to cognitive functioning and mental health. Getting a foothold on the roles and responsibilities of adulthood may be all the more difficult for these one-in-eight non-college youth who use marijuana on a daily or near daily basis. As for college students, we know from our research and that of others that heavy marijuana use is associated with poor academic performance and dropping out of college."
More reading: A two-part review of evidence
U-M College of Kinesiology professor Victor Katch has published a two-part review of cannabis, including history, policy, and available evidence around its medical use, for the Michigan Today publication. Read the pieces here:
Part 1: Cannabis and Health: https://michigantoday.umich.edu/2018/10/17/cannabis-and-health-part-1/
Part 2: Cannabis and Health: https://michigantoday.umich.edu/2018/10/25/cannabis-and-health-part-2/
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