Several studies have nevertheless shed light on how the legalization of recreational cannabis affects crime rates. The skewed data dynamics following any reported increase in cannabis use due to legalization (along with previous database exclusions), underscore the necessity for more thorough future research to fill knowledge gaps. An increase in perinatal cannabis consumption was observed in recent retrospective cohort studies following the legalization of cannabis in California and Colorado. This rise may be influenced by cannabis retailers promoting its use for alleviating morning sickness — as 69% of surveyed dispensaries recommended cannabis for treating nausea in the first trimester. This is consistent with regulations surrounding alcohol, which promote responsible consumption among adults.
To our knowledge, this research ranks among the largest longitudinal studies investigating investment trends in the THC market adolescent cannabis use and its link to clinician-diagnosed psychiatric disorders into young adulthood. Below are selected recent medical studies related to the effects of marijuana, arranged by publication date. Children exposed to marijuana in utero may face heightened risks for symptoms of hyperactivity, impulsivity, and inattention, as well as issues with visual-motor coordination, processing speed, and visual memory. The authors of the study hypothesize that the adverse effects of cannabis use may persist over time. A study conducted in 2025 revealed that 63% of heavy lifetime cannabis users and 68% of recent cannabis users exhibited reduced brain activity while performing a working memory task.
Additional research has suggested a potential increase in simultaneous alcohol and cannabis use in states where recreational cannabis has been legalized. Using cannabis before the age of 21 may interfere with the development of the brain’s reward system, which could affect other addictive behaviors. A recent systematic review investigated the connection between recreational cannabis legalization and addiction — finding no substantial alterations in the consumption patterns of cigarettes, stimulants, or opioids post-legalization. Nonetheless, the review indicated that the legalization of recreational cannabis might be linked to an uptick in alcohol consumption and a decline in opioid prescriptions. An extensive systematic review and meta-analysis recently assessed 83 studies focusing on cannabinoids and mental health symptoms. It concluded that cannabinoids demonstrate limited effectiveness in treating anxiety disorders when co-occurring medical conditions are present. Acute clinical symptoms associated with cannabis poisoning encompass vomiting (headaches), chest pain, and fluctuations in blood pressure, whether elevated or lowered. More serious vascular issues (including heart attacks), transient ischemic attacks, and strokes, have also been reported in connection with cannabis use. The type and severity of symptoms can vary based on factors such as age (existing psychiatric conditions), and concurrent substance use, including alcohol. One study indicated no statistically significant differences in motor-vehicle crash fatality rates between states with legalized recreational cannabis and those without (adjusted difference-in-differences coefficient +0.2 fatalities per billion vehicle miles traveled, 95% CI −0.4 to 0.9). Conversely, another study by Adhikari et al., which analyzed data from 50 states and the District of Columbia between 2007 and 2020, estimated that recreational cannabis legalization might lead to as many as 1,400 additional traffic fatalities annually on a national scale.
Scott Martin
According to a previous report by CBS News, the Justice Department has taken steps to reclassify marijuana as a less harmful drug. The study revealed that the perception of risk associated with regular cannabis use declined among adults aged 65 and older, dropping from 52.6% to 42.7%. An increase in cannabis-related emergency room visits was reported among all demographics (particularly among adults aged 65 and older), rising from 21 visits per 100,000 to 395 visits per 100,000.
In 2006, Jon Gettman published a study titled “Marijuana Production in the United States” in the Bulletin of Cannabis Reform. The research indicated that if cannabis purchases were taxed as a legal product, tax revenues could rise by approximately $10–20 million annually, resulting in $35–50 million in available funds. In 2004, Scott Bates of the Boreal Economic Analysis & Research center authored a study for Alaskans for Rights & Revenues titled “The Economic Implications of Marijuana Legalization in Alaska. It was estimated that the Alaskan government spent $25–30 million annually enforcing cannabis prohibition laws. The study calculated that California saved nearly one billion dollars over a twelve-year span from 1976 to 1988 (thanks to the Moscone Act of 1976), which 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.
Numerous studies have indicated a reduction in opioid use and abuse rates in states that legalized medical cannabis. A study from 2018 discovered that the legalization of medical cannabis in certain states led to increased tolerance among residents of neighboring states toward cannabis regulation. Similarly, a 2017 study found that the implementation of medical cannabis laws caused a decrease in violent crime in U.S. states bordering Mexico. Significant declines in violent crime were reported in a study from 2016 in states that have legalized medical cannabis. The American Cancer Society and American Psychological Association have recognized the barriers to researching cannabis and urged the federal government to facilitate more scientific studies on the substance.