Psychedelics include classic serotonergic hallucinogens (e.g., lysergic acid diethylamide [LSD or “acid”], psilocybin [“magic mushrooms”]), and dissociative agents such as ketamine that can produce mood and cognitive alterations and hallucinations [1,2]. Every year, millions of people around the world use psychedelics [3,4,5]. In the United States (US), psychedelic use prevalence has steadily risen over the past decade [2,3,6], from 1.0% of US adults reporting past-year use in 2014 [7] to 3.6% in 2024, with particularly high rates among those ages 18–25 (6.8%), 26–29 (9.6%), and 30–34 (6.2%) [8].

Research on psychedelic benefits and risks has yielded mixed results [5,9,10,11,12,13,14,15]. Some studies indicate therapeutic benefits for treating various mental health conditions (e.g., major depressive disorder, substance use disorders) and/or longer-term impacts of experiencing a history of trauma (e.g., post-traumatic stress disorder [PTSD]), such as trauma related to adverse childhood events (ACEs) [5,9,10,11,12,13,14,16,17]. Furthermore, some consider self-administered psychedelics as more effective in managing symptoms than other medical treatments [5,18]. However, therapeutic promise exists alongside risks (e.g., misuse, addiction, other mental health conditions), especially when not clinically controlled [15,19,20,21,22,23,24,25,26,27,28]. It remains unclear whether these associations indicate that psychedelic use contributes to these outcomes—or if individuals use psychedelics to treat mental health and substance use disorders [27]. Thus, further research is necessary [29,30,31].

Notably, the 1971 United Nations’ Convention on Psychotropic Substances categorized psychedelics as Schedule 1 substances in 197 countries [32], making recreational psychedelic use nearly globally prohibited [32,33]. However, renewed interest in therapeutic use has led some countries (e.g., Australia, Israel, Canada) to permit psychedelics for medical purposes. Under US federal law (the Controlled Substances Act [CSA], passed in 1970), most psychedelics are classified as Schedule I substances (i.e., no medical use, high potential abuse), but some with mild psychedelic effects are classified differently (e.g., ketamine is Schedule III) [34,35,36]. However, state laws on psychedelics vary [37]. Two states have decriminalized and created regulatory frameworks for psychedelics: (1) in 2020, Oregon legalized psilocybin for therapeutic purposes (e.g., mental health conditions); and (2) in 2022, Colorado legislation created a framework for psychedelic regulation and legalization (covering psilocybin and psilocin offered in “healing centers”) [37]. Certain states have reduced penalties for growing or using psychedelics, some allow medical research, and others are developing/considering new legislation [37]. Within this context, use prevalence has shown particular increases in decriminalized states (i.e., Oregon, Colorado: 3.3% in 2019–2020 to 5.4% in 2021–2023) vs. non-decriminalized states (2.4% to 2.8%) [38].

Psychedelics’ shifting regulatory context is reminiscent of shifts for cannabis in the US. Like psychedelics, cannabis has some medical uses (e.g., pain, muscle spasticity, nausea/vomiting, seizures), but also risks (e.g., use disorder, psychosis, mood disorders, cognitive impairment) [39]. Furthermore, the 1970 CSA also categorized cannabis as a Schedule 1 substance. Recognizing potential medical benefits, in 1996, California became the first state to legalize medical use. By December 2025, 40 states, DC, Puerto Rico, Guam, and the US Virgin Islands, have laws allowing medical use [40]. States have also legalized nonmedical (i.e., ‘recreational’) cannabis, starting in 2014 in Colorado and Washington; as of 2025, 25 states fully legalized cannabis for both nonmedical and medical use [40]. Notably, use prevalence has increased over the past decade, from 12.1% of US adults reporting past-year cannabis use in 2014 [7] to 23.4% in 2024, with particularly high rates among those ages 18–25 (35.0%), 26–29 (37.7%), and 30–34 (31.7%) [8].

Perceptions of these products are important for understanding their use and the extent to which the population will support continued legal expansion. One UK-based study found that viewing drug use as a health issue, rather than a criminal issue, predicted lower perceived risk and greater psychedelic legalization support [41]. US-based studies found that psychedelic use was perceived as posing a range of psychospiritual benefits (e.g., enhanced life meaning, spirituality) but more risks (e.g., bad “trips,” accidents, impaired judgment, legal problems) [42], and that recreational use was perceived as having negative health consequences while therapeutic use was perceived as having positive health consequences [43]. Similarly, cannabis perceptions (e.g., risks, social acceptability) and interest in its medical utility in the US have generally become more favorable over the past decade [44,45,46,47,48], which have coincided with increased support for cannabis legalization [44,49].

Perceptions and attitudes are shaped by exposure to information. A US-based survey found that prominent sources of adults’ information about psychedelics were their own experiences (80%), online (e.g., websites 62%, discussion forums 57%), friends (61%), books (57%), and scientific articles (55%) [50]. Similarly, studies have documented various cannabis information sources communicating both benefits (e.g., advertising, retailers, friends/family, online) and risks (e.g., public health campaigns, warning labels, friends/family, online) [51,52,53,54,55]. Unfortunately, many of these sources may include misinformation—either intentionally or unintentionally [56,57].

Given the parallels between psychedelics and cannabis and the more recent shifts in the psychedelic regulatory and use context, it is crucial to examine attitudes and use outcomes that can inform legislative, regulatory, and prevention efforts. Factors associated with use and support for decriminalization/legalization may be similar across these substances and thus are important to understand [58]. One relevant theoretical framework for understanding how populations form opinions about ideas over time is diffusion of innovation (DOI) theory [59,60,61]. DOI posits that communication is key to shaping opinions and that support increases as the proportion of the population that favorably perceives the idea increases and expands communication about potential benefits [59,60,61]. This theory also suggests the importance of exposure to relevant information (both favorable and unfavorable), as these exposures influence perceptions and attitudes, and ultimately behavior [59,60,61]. Thus, factors associated with use and support for decriminalization/legalization likely include exposure to information, highlighting both benefits and risks, as well as perceived risk and social acceptability. Additionally, given these substances’ potential therapeutic utility, whether individuals experience mental health symptoms or historic trauma like ACEs may also impact their perceptions of these substances [5,9,10,11,12,13,14,16,17,39]. This study assessed cannabis and psychedelic use, use intentions, and legalization support, as well as potential correlates (mental health, ACEs, promotional and risk-message exposure, perceived risk and social acceptability). Message exposure, perceptions, use intentions, and legalization support for cannabis vs. psychedelics were also compared.