The participants, many of whom were born in Colorado and Minnesota but had since moved, were surveyed before and after 2014 on how many days they had used cannabis in the past six months, and scientists initially found there was an increase of about 24% in use in states that have legalized recreational cannabis compared to those that have not. Based on where respondents lived at the time of the surveys, nearly every state was represented, along with Washington, DC, and Puerto Rico.
The study also included 111 pairs of identical twins, one of whom lived in a state that legalized recreational cannabis and the other in a state that did not. Among identical twins, the researchers found that use increased about 20% in states that legalized recreational cannabis compared to those that did not.
Since identical twins share so many similarities, that percentage is a more accurate estimate of the causal influence of cannabis legalization on cannabis use, said study lead author Stephanie Zellers, now a researcher at the University of Helsinki in Finland. .
Identical twins share the same genes and often the same type of upbringing, which could influence how often someone uses cannabis, said Zellers, who was a doctoral candidate in psychology at the University of Minnesota at the time. of the project.
“Because that 20% estimate comes from analysis controlling for measured and unmeasured variables,” Zellers said, “it is the most accurate estimate of the causal influence of cannabis legalization on cannabis use.”
Many states that, like Colorado, have legal recreational cannabis also have a large number of dispensaries, making purchases easy, a factor that could have contributed to the higher rate of use, Zellers said.
No legal consequences, such as fines or jail time, could also affect the increased use in recreational states, he added.
“In addition, the existence of recreational policies influences the perception of cannabis use,” said Zellers, “making it seen as safer and less stigmatized.”
How legalization affects use
As more states legalize recreational cannabis use, it’s important to recognize how that legalization affects use, said Dr. Nora Volkow, director of the National Institute on Drug Abuse at the National Institutes of Health.
“This knowledge can be used to inform strategies to implement legalization while minimizing potential harms,” said Volkow, who was not involved in the study.
The statistics could also help researchers understand how recreational use affects the rate of cannabis addiction, he said.
In states where recreational use is legal, ads often label the drug as safe, Volkow said.
More research needs to be done on how safe cannabis is and its impact on the body before people jump to conclusions about safety. she said.
it’s not black and white
“People often want to say that cannabis is good or bad,” Volkow said. “But in biology, nothing is black and white, there is a lot of gray.”
Frequent or long-term cannabis use is associated with health problems such as chronic bronchitis and schizophrenia, he said.
However, its use has also been shown to be effective in treating some painful conditions, such as nausea and vomiting, Volkow said.
Zellers said he hopes to do more research on the effects of increased cannabis use on conditions such as mental health and addiction.