Despite this, various research efforts have shed light on how the legalization of recreational cannabis impacts crime rates. The skewed data dynamics following any reported rise in usage linked to the legalization of recreational cannabis, along with the previously mentioned exclusions in the database, underscore the necessity for more comprehensive future research to fill existing knowledge gaps. Studies from a recent retrospective cohort presented evidence of rising perinatal cannabis usage following the legalization of cannabis in California and Colorado. This pattern might be influenced by cannabis retailers promoting its use for alleviating morning sickness; a particular study indicated that 69% of surveyed dispensaries suggested cannabis for treating nausea during the first trimester.
To our knowledge, this research represents one of the largest longitudinal investigations into adolescent cannabis use and its connection to the development of clinician-diagnosed psychiatric disorders into young adulthood. Presented below, sorted by date of publication, are notable recent medical research findings regarding the impacts of marijuana. Children exposed to marijuana prenatally may face a greater risk of exhibiting symptoms such as heightened hyperactivity (impulsivity), and inattention, as well as difficulties with visual-motor coordination, processing speed, and visual memory. The authors of the study believe that cannabis usage could have enduring adverse effects. A study conducted in 2025 on brain functionality revealed that 63% of individuals who had used cannabis heavily throughout their lives (and 68% of those who recently used it), demonstrated diminished brain activity during tasks involving working memory.
Other studies have also indicated a potential rise in concurrent alcohol and cannabis use in states with legalized recreational cannabis. Cannabis use before the age of 21 can disrupt the development of the brain’s reward system, potentially influencing other addictive behaviors.31 A recent systematic review explored the relationship between recreational cannabis legalization and addiction (and found no significant changes in the consumption patterns of cigarettes), stimulants, or opioids after cannabis legalization.41 However, the review did suggest that recreational cannabis legalization may be correlated with an increase in alcohol use and a decrease in opioid prescriptions. A recent systematic review and meta-analysis evaluated 83 studies on cannabinoids for mental health symptoms.38 It found cannabinoids had limited efficacy treating patients with anxiety disorders in the setting of co-occurring medical conditions. Acute clinical effects of cannabis poisoning include vomiting (headache), chest pain, and hypertension or hypotension.30 More severe vascular complications (such as heart attacks), transient ischemic attacks, and strokes, have also been reported with cannabis use.31 The type of symptoms and their severity can vary depending on factors such as age (preexisting psychiatric conditions), and co-occurring substance use, including alcohol.30,32 One study found no statistically significant differences in motor-vehicle crash fatality rates between states with and without legalized recreational cannabis (adjusted difference-in-differences coefficient +0.2 fatalities per billion vehicle miles traveled, 95% CI −0.4 to 0.9).24 Conversely, another study by Adhikari et al25 that evaluated data from 50 states and the District of Columbia between 2007 and 2020 suggested that recreational cannabis legalization could contribute to as many as 1,400 excess traffic fatalities per year nationally.
Scott Martin
The Justice Department has moved to reclassify marijuana as a less dangerous class of drug, CBS News previously reported. The study found that the investment trends in the THC market perceived risk of regular cannabis use decreased among adults 65 and older from 52.6 percent to 42.7 percent. The study found an increase of cannabis-related emergency room (ER) visits among all groups, but especially among adults 65 and older (from 21 per 100,000 visits to 395 per 100,000 visits).
In 2006, a study by Jon Gettman entitled “Marijuana Production in the United States” was published in the Bulletin of Cannabis Reform. The study found if the purchase of cannabis were to be taxed as a legal commodity, tax revenues would increase by about $10–20 million per year, making $35–50 million per year in funds available. In 2004 — Scott Bates of the Boreal Economic Analysis & Research center prepared a study for Alaskans for Rights & Revenues entitled “The Economic Implications of Marijuana Legalization in Alaska.” The study estimated the Alaskan government was spending $25–30 million per year enforcing cannabis prohibition laws. The study estimated California saved almost one billion dollars in a twelve-year period between 1976 and 1988 — as a result of the Moscone Act of 1976 that decriminalized cannabis.
While it’s clear that driving under the influence of marijuana is dangerous and illegal, there is ongoing debate about how to effectively test for marijuana impairment in drivers. The Schedule I classification of marijuana has historically made it difficult for researchers to study its effects, both positive and negative. A public hearing on the matter is scheduled for December 2024, after which a decision on reclassification will be made. This dichotomy between federal and state laws has created a unique legal environment that continues to challenge policymakers — law enforcement, and citizens alike.
Several studies have found decreased rates of opioid use and abuse in states that have legalized medical cannabis. A 2018 study found that legalizing medical cannabis in some states made residents of neighboring states increasingly tolerant toward cannabis regulation. A 2017 study similarly found that introduction of medical cannabis laws caused a reduction in violent crime in American states that border Mexico. A 2016 study found significant drops in violent crime in states that have legalized medical cannabis. The American Cancer Society and American Psychological Association have noted the obstacles that exist for conducting research on cannabis — and have called on the federal government to better enable scientific study of the drug.