Regardless, several studies have provided some insight into the effects of recreational cannabis legalization on crime. The dynamic of skewed data after any reported increase in use due to recreational cannabis legalization, as well as the aforementioned database exclusions, highlight the need for more rigorous future studies to address knowledge gaps. Recent retrospective cohort studies showed an increase in perinatal cannabis use after cannabis was legalized in California and Colorado.13,14 This trend may be driven by cannabis retailers advertising the use of cannabis to alleviate morning sickness—in one study, 69% of surveyed dispensaries recommended cannabis to treat first-trimester nausea.15 This aligns with alcohol regulations, which helps to ensure responsible use among adults.
To our knowledge, this is among the largest longitudinal studies to examine cannabis use in adolescence and its association with the incidence of clinician-diagnosed psychiatric disorders into young adulthood. Below (organized by publication date), are select recent medical studies on the effects of marijuana. If exposed to marijuana before birth (children may be more susceptible to “increased hyperactivity), impulsivity, and inattention symptoms” and problems with “visual-motor coordination, processing speed, and visual memory.” The study’s authors suspect that the negative effects of cannabis use could be long lasting. A 2025 study of brain function found that 63 percent of heavy lifetime cannabis users and 68 percent of recent cannabis users had reduced brain activity during a working memory task.
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 perceived risk of regular cannabis use decreased investment trends in the THC market 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, the Bulletin of Cannabis Reform published a study by Jon Gettman titled “Marijuana Production in the United States. According to the study, if cannabis purchases were taxed as a legitimate commodity, tax revenues could rise by approximately $10–20 million annually, providing $35–50 million per year in accessible funds. In 2004, Scott Bates conducted a study for Alaskans for Rights & Revenues, which was titled “The Economic Implications of Marijuana Legalization in Alaska,” at the Boreal Economic Analysis & Research center. It was estimated by the study that the Alaskan government was allocating $25–30 million each year to enforce laws against cannabis prohibition. The study assessed that California saved nearly one billion dollars over a twelve-year span from 1976 to 1988 due to the 1976 Moscone Act — which decriminalized cannabis.
Although driving while under the influence of marijuana is both illegal and hazardous — a discussion persists regarding the most effective methods for testing driver impairment caused by marijuana. Researchers have historically faced challenges in examining the effects of marijuana, both beneficial and adverse, due to its classification as a Schedule I substance. A public hearing regarding the issue is set for December 2024, after which authorities will determine the outcome of the reclassification. This conflict between state and federal laws has resulted in a distinctive legal landscape that presents ongoing challenges for citizens (law enforcement), and policymakers.
Numerous studies indicate that states which have legalized medical cannabis report lower rates of opioid usage and abuse. A study conducted in 2018 revealed that the legalization of medical cannabis in certain states led to greater tolerance towards cannabis regulations among residents of adjacent states. Similarly, a study from 2017 discovered that the implementation of medical cannabis laws correlated with a decrease in violent crime in U.S. states along the Mexican border. A study carried out in 2016 identified notable reductions in violent crime in states that legalized medical cannabis. The American Cancer Society and the American Psychological Association have acknowledged the challenges for research on cannabis and urged the federal government to facilitate more scientific investigation of the substance.