Over 30 million psychedelic users in the United States

We estimated lifetime prevalence of psychedelic use (lysergic acid diethylamide (LSD), psilocybin (magic mushrooms), mescaline, and peyote) by age category using data from a 2010 US population survey of 57,873 individuals aged 12 years and older. There were approximately 32 million lifetime psychedelic users in the US in 2010; including 17% of people aged 21 to 64 years (22% of males and 12% of females). Rate of lifetime psychedelic use was greatest among people aged 30 to 34 (total 20%, including 26% of males and 15% of females).


Introduction
The classical serotonergic psychedelics, LSD (lysergic acid diethylamide), psilocybin ("magic mushrooms"), and mescaline (peyote and other cacti), have their main mechanism of action at the serotonin 2A receptor (5-HT 2A ), produce similar, often indistinguishable subjective effects, and elicit cross-tolerance 1,2 . The mechanisms of action, subjective effects, and risk profile of the classical serotonergic psychedelics distinguishes them from other drugs sometimes also labeled "hallucinogens", such as entactogens, like methylenedioxymethamphetamine (MDMA; ecstasy) that act primarily at serotonin transporters, or dissociative anesthetics, like phencyclidine (PCP) or ketamine that act primarily at NMDA glutamate receptors 1 .
Prevalence data on psychedelic use in the US is often reported for LSD alone (ignoring psilocybin and mescaline), or for psychedelics grouped together with PCP (popular in the 1970s), MDMA (popular since the 1990s), and/or other "hallucinogens" (some older estimates of hallucinogen use even included cannabis, amphetamine, and cocaine as hallucinogenic drugs), or for use among teenagers but not adults. Here, we present estimated lifetime prevalence of psychedelic use by age category using data from a large US population survey.

Methods
We examined the estimated lifetime use of psychedelics by age based on 2010 data of the National Survey on Drug Use and Health (NSDUH). Results are presented for males and females separately. We counted participants as having any lifetime psychedelic use if they reported ever using LSD, psilocybin, mescaline, or peyote. The use of mescaline and peyote were combined into one category because mescaline is the active substance of the peyote cactus, but peyote use was also examined separately. Current age was only available as a categorical variable. This study was exempt from review by our Regional Committee for Medical Research Ethics because all data are available in the public domain without any identification of personal information.

Data source
The annual NSDUH survey provides estimates of substance use and mental health indicators from a randomly-selected sample representative of the US civilian non-institutionalized population aged 12 and older. The Substance Abuse and Mental Health Services Administration (SAMHSA) of the US Department of Health and Human Services is responsible for the NSDUH study design and methods of assessment. Trained interviewers met the randomlyselected participants in their homes, and participants listened to recorded questions via headphones and then entered their answers directly into a computer, providing a highly confidential and standardized setting. The response rate was approximately 78%. In addition, approximately 10% of participants were excluded from the public use data file, either because of excessive missing data on drug use or because they were excluded at random in order to increase anonymity. The total number of respondents in the public use file was 57,873. Detailed information on the sampling and data collection methods, including interview instructions and questionnaires, confidentiality and informed consent are available on the SAMHSA website (http://oas.samhsa.gov/nsduh.htm).

Data analysis
Estimates were calculated using the online Survey Documentation Analysis from the Inter-university Consortium for Political and Social Research (http://dx.doi.org/10.3886/ICPSR32722.v3). Calculations of estimated population percentages and extrapolated total numbers of psychedelic users in the US took into account the weights provided with the NSDUH public use data file. Variance estimates took into account the complex sample design of the NSDUH survey using Taylor series linearization. Respondents with missing data on psychedelic use (less than 1% of the respondents) were assumed to have no use.

Discussion
Psychedelics continue to be widely used in the US. Common reasons given for using psychedelics include curiosity, mystical experiences, and introspection 3 . Rates of lifetime psychedelic use are greater in males than in females. Overall rates of lifetime psychedelic use are roughly the same among the "baby boomers" and younger adults. However, psilocybin was more common among younger adults, while LSD and mescaline or peyote were more common among older adults. Use of psilocybin mushrooms has increased since the 1970s in the US and worldwide, likely due to dissemination of simple home cultivation techniques, instructions on finding wild mushrooms, and information about effects and methods of psilocybin mushroom use 4 . This was a retrospective cross-sectional study. Self-reports of drug use behaviors could be influenced by memory errors and under-reporting; however, a their age and sex. How are they characterised by SES, education, geographic areas of residence and experience with other illicit drugs e.g. cannabis, MDMA and stimulants? 5. What if anything follows from the findings? Should we be concerned about this use or should we regard psychedelic drug use as being of much lower public health concern than the use of other illicit drugs such as cannabis, amphetamine type stimulants, cocaine and opioids? I have read this submission. I believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.
No competing interests were disclosed. Competing Interests: