Psychedelic drug use may be about as common now in the United States as it was in the 1960s generation, according to new data analysis. It seems that young Americans today are as apt to use substances like LSD and psilocybin during their lifetimes as their baby boomer parents were in their heyday.

Hallucinogens like LSD (lysergic acid diethylamide), psilocybin ("magic mushrooms"), mescaline, and peyote were popularized by countercultural members of the American "baby boom" generation during the 1960s, promoted as a means of expanding consciousness and introspection.

Such substances alter mood and perception by stimulating brain receptors of the neurotransmitter serotonin, which can cause hallucinations, sensory distortions, confusion, and intense emotions. They are valued by recreational users for what LSD inventor Albert Hoffman called "an inner joy" and "open mindedness."

In the United States, such drugs have been banned as Schedule I controlled substances since the Controlled Substances Act of 1970, which found no medical value and a high potential for abuse in psychedelics.

In recent years, however, researchers have identified psychedelic drugs as promising therapeutic agents for conditions as varied as alcoholism, PTSD, major depression, anxiety, and impending death. Activists suggest that laws restricting their use were a hasty reaction to the cultural upheaval of the 1960s, and should be revised in light of their apparent scientific merit.

Neuroscientists from the Norwegian University of Science and Technology decided to investigate how the prevalence of recreational psychedelic drug use has persisted in the United States over time, despite such restrictive laws.

In their research, they distinguished the use of psychedelics like LSD, psilocybin, and mescaline, which have similar effects because they act primarily on the serotonin 2A receptor in the brain, from other drugs commonly called hallucinogens like MDMA ("ecstasy) or ketamine, which have different mechanisms of action.

"Psychedelics are different from other drugs, in that they are not known to be physically harmful or cause addiction or compulsive use," said researchers Teri S Krebs and Pål-Ørjan Johansen in a news release. "Experts agree that psychedelics are less harmful than alcohol and most other recreational drugs, although psychedelics can elicit anxiety and confusion during the drug effects."

They examined data from the 2010 National Survey on Drug Use and Health (NSDUH), which surveyed 57,873 randomly selected Americans about their drug history, in order to determine the lifetime use of psychedelic drugs in that representative sample of the American population.

The results, published in F1000Research last month, indicate that about 32 million Americans have used any psychedelic drugs at least once in their lifetimes— about 17 percent of all American adults between the ages of 21 and 64. The survey data do not specify when in their lifetimes respondents used such drugs.

"Overall rates of lifetime psychedelic use are roughly the same among the 'baby boomers' and younger adults," wrote the researchers, and the drugs continue to be widely used in the United States and worldwide.

Lifetime psychedelic drug use among baby boomers aged 50 to 64 was on par with that of younger adults aged 21 to 25, about 15 percent. The highest rate was among adults aged 30 to 34- over 20 percent. Adults over the age of 65 largely missed the advent of psychedelic drugs in popular culture, since only 1 percent reported using them.

Men were more likely to have used psychedelics than women, regardless of age categories.

There were, however, generational differences in the types of psychedelic drugs most commonly used. LSD, mescaline, and peyote were more common among older adults, while younger adults were more likely to use psilocybin mushrooms.

The researchers attribute the difference to the rising worldwide use of psilocybin since the 1970s. A 2009 paper suggested that this increase is due to the wide availability of information about how to cultivate the mushrooms, compared to what previous generations had access to.

Krebs and Johansen conclude that psychedelic drugs have not declined in popularity among young Americans since the 1960s. Their conclusion seems to highlight the value of recreational use over scientific potential:

"People often report mystical experiences as a major reason for using psychedelics," they said in the news release. "Archaeological evidence shows that psychedelic plants have been used in the Americas for over 5000 years, and currently around 300,000 people in the US enjoy a recognized religious freedom right to use psychedelics."