As a teenager, Johns Hopkins psychiatrist Christopher Hammond was concerned to see several friends develop problems related to cannabis, alcohol and opioid use that dramatically impacted their health and life trajectories. Today, he directs a full research program dedicated to understanding how cannabis and other drugs affect brain development as well as physical and mental health in young people, with an eye toward finding new ways to prevent and treat cannabis use and other substance-related problems in that population.

“Substance use and addictive behaviors really begin for the majority of people during adolescence, which is a period of time where the brain is still maturing and is more sensitive to the effects of exposure to drugs,” says Hammond, who is medical director of Johns Hopkins’ Co-occurring Disorders in Adolescents and Young Adults Clinic. The facility is for patients with substance use and mental health conditions and their families. In the past five years, he has expanded his research to examine how changing state-level cannabis laws in the United States influence young people’s societal perceptions, cannabis use patterns and mental health outcomes.

A study, published in the Journal of the American Academy of Child & Adolescent Psychiatry, found that legalization of medical and recreational marijuana was associated with increased suicide-related mortality among female youth and among boys and girls age 14 to 16. A follow-up study, presented at last year’s American Academy of Child and Adolescent Psychiatry’s annual meeting, in October, found similar associations among Hispanic and Asian youth.

Hammond is now looking into why this occurs.

“One of our hypotheses is that adolescents living in states that have enacted cannabis laws, particularly recreational cannabis laws, may have increased their cannabis use, or shifted to using higher potency products containing more delta-9-tetrahydrocannabinol” (THC), he says, noting such factors might influence mental health symptoms and lead to a higher likelihood of suicide-related attempts and deaths.

Other investigators’ studies have shown that an increase in cannabis use and cannabis vaping among Hispanic youth mirrors a similar increase among Hispanic adults living in states that have legalized cannabis. Hammond believes these parallel trends may reflect changes in parental attitudes and parenting practices regarding adolescent cannabis use or mental health treatment that are more pronounced for Hispanic families because of legalization.

Hammond’s research also examines clinical and neural correlations regarding youth cannabis use. In a study recently published in Substance Use & Misuse, he and collaborator Carol Vidal, a Johns Hopkins psychiatrist, found an association between past-month cannabis use and adverse psychosocial functioning, including higher rates of suicidal thoughts among North American college students.

Another study, recently completed by Hammond’s group and published in Brain Sciences, looked at “meta-analyzing” functional MRI studies that examined neural effects of cannabis use among youth. This study found that cannabis use during adolescence was associated with alterations in brain function in medial prefrontal cortical and insular brain regions during cognitive task. The study measured executive functioning, emotional reactivity and regulation, and processing of rewarding stimuli.

With a grant from the National Institute on Drug Abuse, Hammond and his colleagues are now examining variations among state cannabis laws to see which provisions, such as potency limits, advertising restrictions and purchase quantity limits, may contribute to or reduce health risks for young people. This research could help inform evidence-based policy adjustments regarding cannabis and how it is distributed, with the goal of minimizing risk to vulnerable subgroups that are negatively impacted by these laws.