Study reveals impact that legalization of marijuana have on teens

Oregon study raises concerns about the connection between legalization and teen health.

Study reveals impact that legalization of marijuana  have on teens
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The legalization of marijuana use continues to sprout in states willing to pass such laws, partially due to voter demand and also the lure of greater tax revenue.

We will focus on Oregon in this article for two reasons. First, the ratio of Oregonians using cannabis outpaced the general U.S. population by nearly 40 percent from 1999 through 2005. Second, Oregon has recently studied the effect of marijuana legalization on teens.

In 2015, Oregon Governor Kate Brown signed a bill declaring marijuana sales legal to recreational users from dispensaries starting October 1, 2015. State officials began working on establishing a regulatory structure for sales of marijuana, and taxing of such sales, with the Oregon Liquor Control Commission (OLCC) to oversee it. Effective January 1, 2017, dispensaries were no longer permitted to sell cannabis for recreational use unless they applied for, and received, an OLCC license for such sales. From early December 2016 to early January 2017, the number of retailers licensed to sell recreational marijuana grew from 99 to 260, and hundreds more applications continue to be received and processed.

The Oregon Research Institute (ORI) has released the results of a study about the effect of legalized marijuana on teens and youth in general. Those results are published online in Psychology of Addictive Behaviors.

Results of the study

Recent results from the ORI indicate that the influence of legalization on youth may depend on whether they were already using at the time of legalization. Following the legalization of recreational marijuana, no significant changes in the numbers of youth who used marijuana occurred, yet increases in the frequency of use by youth who were already using marijuana were found. 

For teenagers who had tried marijuana by 8th grade, the frequency of use during the following year increased 26% more for those who were in 9th grade after marijuana was legalized compared to those who were in 9th grade prior to legalization.

"When making policy decisions about marijuana, it is important to consider how those policies can effect teenagers. Although legalization of recreational marijuana prohibits use in those under 21, changes in youth attitudes toward marijuana, age of initiation, and frequency of use may occur," said Julie C. Rusby, Ph.D., principal investigator of the research.

When Oregon began legal sales of recreational marijuana in October 2015, Rusby and her team were perfectly positioned. Their study examining substance use among Oregon 8th and 9th graders was already underway and investigators were able to collect data about youth marijuana use before and after legalization. Additionally, Oregon allowed counties and cities to prohibit marijuana sales, so investigators examined the impact of community sales policy on teenagers' use. 

Teenagers from 11 rural and suburban middle schools in seven Oregon school districts answered surveys about their marijuana use, attitudes towards marijuana, and willingness to use marijuana. Their parents answered questions about their own use of marijuana.

The association of legalization with changes in youth marijuana use varied by the sales policy of the community. Youth surveyed prior to legalization from communities that later prohibited sales were less likely to increase willingness and intent to try marijuana compared to those from communities that later allowed sales. Similarly, youth surveyed prior to legalization from communities prohibiting sales increased marijuana use at a lower rate by the spring of ninth grade compared with youth in communities with sales. 

Youth surveyed post-legalization from communities with marijuana sales had lower rates of marijuana use during spring of eighth grade and increased marijuana use almost twice as much by the spring of ninth grade compared with the other groups. There were no differences for legalization and community policy on parent report of their own use.

Usage Trends

According to results from the 2018 National Survey on Drug Use and Health. An estimated 43.5 million individuals reported using marijuana during the past year. Survey results reveal that marijuana use is widespread among young people. Some statistics of its use include:

3.1 million adolescents aged 12 to 17 (about 1 in 8) used marijuana in the past year

• 11.8 million young adults aged 18 to 25 (about 1 in 3) used marijuana in the past year

• 14% of 8th graders have used marijuana in their lifetime

• 33% of 10th graders have used marijuana in their lifetime

• 44% of 12th graders have used marijuana in their lifetime

• 22% of 12th graders have used marijuana in the past month

• 6% of 12th graders (about 1 in 16) use marijuana on a daily basis

The National Institute on Drug Abuse (NIDA) reports that marijuana use can have much more long-term effects for teenagers. The teenage brain is not yet fully mature, with neurodevelopment continuing until at least the early or mid-20s. During adolescence the brain is particularly sensitive to drug exposure, and marijuana use impacts how connections are formed within the brain. Other effects on the developing brain include interference with neurotransmitters and abnormal brain shape and structure volume.

NIDA Studies also have shown that the use of marijuana is associated with reduced cognitive function in teens. One study found that teens who regularly use marijuana lose an average of 5.8 IQ points by the time they reach adulthood. A recent study found that marijuana has a more negative impact on a teenager’s cognitive development than alcohol.

Other long-term risks associated with marijuana use include respiratory issues, increased chance of lung cancer and heart attack, problems with child development during and after pregnancy, and the development of Cannabinoid Hyperemesis Syndrome (characterized by cycles of severe nausea, vomiting, and dehydration that may require emergency medical attention).

Oregon study conclusions

"In states that legalize recreational marijuana, the study results point to the importance of preventing youth who use marijuana from escalating their use," noted Rusby.

The results indicate there may be an immediate impact of legalization for youth who had already initiated marijuana use because they increased their use after legalization. This was true even in communities that prohibited recreational marijuana sales, indicating that community sales policies may not effectively reduce the frequency of use by teenagers.

Research that follows up teenage marijuana use post-legalization for a longer period of time and in different locations could further contribute to inform marijuana policy. 

Prevention campaigns that educate youth of the risks of using marijuana while their brains are still developing, and building capacity and resources for parents to discuss marijuana with their adolescent children, may provide guidance as communities and states navigate the new landscape of legal recreational marijuana.


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Frank Racioppi
See all posts by Frank Racioppi