Marijuana Policy Project

Researchers at the Institute for Child Health Policy at the University of Florida College of Medicine examined what effect, if any, medical marijuana laws have on teen use. U.S. anti-drug officials like the drug czar have said such laws decrease the perception of risk and therefore lead to an increase in teen use. Looking at data from 2003-2011 from Montana, Rhode Island, Michigan, and Delaware, these researchers found "no discernible pattern suggesting an effect on either self-reported prevalence or frequency of marijuana use." They conclude that passage of medical marijuana laws does not measurably affect adolescent marijuana use.

Replicating a prior study, but controlling for state characteristics and measurement error, researchers found that medical marijuana laws have little discernible impact on teen marijuana use or perceptions of the risk of marijuana use in those states. In fact, their research showed that passage of medical marijuana laws actually resulted in a slight decrease in teen marijuana use.

This article examines the subjective impact of medical cannabis on the use of both licit and illicit substances via self-report from 404 medical cannabis patients recruited from four dispensaries in British Columbia, Canada. A 44-question survey was used to anonymously gather data on the self-reported impact of medical cannabis on the use of other substances. Over 41% state that they use cannabis as a substitute for alcohol, 36.1% use cannabis as a substitute for illicit substances, and 67.8% use cannabis as a substitute for prescription drugs. The three main reasons cited for cannabis-related substitution are “less withdrawal,” “fewer side-effects,” and “better symptom management.”

Using data from the national and state Youth Risk Behavior Surveys and other government sponsored data collections, researchers from the Universities of Washington, Oregon, and Colorado at Denver found no association between medical marijuana laws and increased teen marijuana use. They concluded, "[o]ur results are not consistent with the hypothesis that legalization leads to increased use of marijuana by teenagers."

Applying the "routine activities theory" of crime, this NIDA-funded study used data from 95 census tracts in Sacramento to analyze two types of crime (violent and property) in areas with varying concentrations of dispensaries. Results indicated that while factors traditionally understood to lead to increased crime ��� large percentages of land zoned for commercial rather than residential use, a high percentage of one-person households, the presence of highway ramps, a higher percentage of the population being ages 15-24 ��� were positively associated with crime in those areas, the density of medical marijuana dispensaries was not associated with violent or property crime rates. In their conclusion, the researchers theorize that measures dispensaries take to reduce crime (i.e., doormen, video cameras) may increase guardianship, thus deterring crime.

This report by Release.org, a British organization focused on harm reduction in drug policies, looked at data from over 20 countries that have adopted some form of decriminalization of drug possession, including several that have only decriminalized marijuana possession. It found that decriminalization did not lead to significant increases in drug use in those countries, strongly indicating that harsh penalties for possession have little to no effect on drug use rates.

Replicating prior published study results that showed higher marijuana use rates in states with medical marijuana laws, researchers examined the link between those laws and teen marijuana use. Results showed that medical marijuana laws "decreased past-month use among adolescents by 0.53 percentage points and had no discernible effect on the perceived riskiness of monthly use," leading the authors to conclude that evidence linking medical marijuana laws to increased teen marijuana use was "limited."

Using a controlled setting, researchers observed seven continuous days of abstinence in 25 heavy marijuana users to quantify the concentration of 9-tetrahydrocannabinol (THC) in subjects' blood. Results showed that nine had no measurable THC content in their blood throughout the study, while 16 had at least one positive result (at least .25 ng/mL), though not necessarily on the first day. Surprisingly, on the last day of the study, six full days after entering the unit, six participants still displayed detectable THC concentrations, with the highest day-seven results yielding 3.0 ng/mL, leading the researchers to conclude that, "substantial whole blood THC concentrations persist multiple days after drug discontinuation in heavy chronic cannabis users."

Comparing heavy marijuana users with clinical anxiety symptoms to demographically equivalent heavy marijuana users with no anxiety symptoms, the authors found that "among several psychological variables (including anxiety, depression, schizotypy, and impulsivity), anxiety was most strongly predictive of amount of marijuana used and marijuana-related problems."

Comparing 101 youths (ages 12-22) with positive symptoms of psychosis to 59 healthy controls of the same age over a period of three years, this study's authors found that, of those clinically predisposed to psychosis, those who used marijuana tended to demonstrate better social functioning. Results also showed that lifetime marijuana use or abuse did not lead to psychosis, even among those youths clinically predisposed to psychosis.

Examining two separate meta-analyses of the long term negative cognitive impact of heavy marijuana use, the authors of this study conclude that, while cognitive performance is negatively affected by cannabis use, the negative effects appear to completely wear off within a month of cessation.

This analysis of the anti-cancer properties of cannabidiol, a non-psychoactive constituent of marijuana, studied its effect on mice and found that it reduced polyps, tumors, and other carcinogenic precursors, and in colorectal carcinoma cell lines, "protected DNA from oxidative damage, increased endocannabinoid levels and reduced cell proliferation," leading the authors to conclude that cannabidiol does exert a chemopreventive effect.

This meta-analysis of 38 other randomized-controlled trials that studied the use of cannabis based treatments found that, of these, 27 (71%) "concluded that cannabinoids had empirically demonstrable and statistically significant pain-relieving effects" while 11 (29%) did not.

This double-blind, randomized trial compared the effects of cannabidiol, a non-psychoactive constituent of marijuana, to amisulpride, a potent antipsychotic, in treatment of acute schizophrenia. Results showed that both treatments were safe and effective, but treatment by cannabidiol involved a much safer side-effect profile and presented greater evidence of long-term clinical improvement.

This placebo-controlled, crossover study on the effects of smoked marijuana on spasticity, a common and difficult to treat symptom of multiple sclerosis, found that marijuana was significantly more effective than placebo at both reducing muscle spasticity and patients' pain sensations.

This review describes short and long term negative effects of marijuana use from a cost-benefit perspective.

Prohibitionists sometimes claim marijuana causes depression and scoff at marijuana as a treatment for depression. Here a Viennese doctor describes repeated clinical successes using oral THC to treat depression.

This rather complicated study looks at the "gateway theory" through data collected from 510 pairs of twins who participated in a very large, long-term health study -- and the gateway theory doesn't emerge with much backing.