In the summer and fall of 2020, researchers at New York University conducted an in-depth analysis of marijuana use data from the most recent National Survey on Drug Use and Health (NSDUH). The study, released online in January 2021 and scheduled for publication in February 2021, assessed quarterly trends in past-month marijuana use among people age 12 and over between 2015 and 2019. The goal of the study was to gain a detailed understanding of patterns of marijuana use over the calendar year. Researchers wanted to learn when use increased, when it decreased, and when it stayed the same, in order to tailor mitigation and prevention strategies and maximize their impact.

The study included responses from 282,768 individuals and focused on this survey question:

How long has it been since you last used marijuana or hashish?

Researchers then organized answers that indicated participants used marijuana or hashish in the past month into quarterly groups: January through March (Quarter One/Q1), April through June (Quarter Two/Q2), July through September (Quarter Three/Q3), and October through December (Quarter Four/Q4).

The trends they found were consistent across all groups and over the five years of data analyzed.

Consistent for all groups except for one: teenagers.

Marijuana Use Increases Over the Year for Most Age Groups

Here’s an overview of what the researchers found:

• Past-month marijuana use increased 38.2% for all groups between 2015 and 2019
• In each calendar year, past-month marijuana use increased from an average of 8.9% in Q1 to 10.1% in Q4 for all groups, with the exception of adolescents age 12-17
• The largest increase in use from 2015-2019 occurred in adults over the age of 65, who showed a 52.7% increase in past-month use
• Past month use increased for people without a prescription for medical marijuana use and for people without a diagnosis of cannabis use disorder

We’ll get to the teen-specific data in just a moment, after we address some of the interesting bits of information embedded in the data above.
The first item of note is that the in-year rise and fall of marijuana use for each year was consistent over the five years examined. While overall use rose consistently between 2015 and 2019, marijuana use was highest in Q4 of each year and lowest in Q1. Researchers suggest this pattern was related to the common practice of having a dry January or making a New Year’s Resolution to quit using marijuana. But those are only guesses, since the survey questions did not ask people to identify the reasons they did or did not use marijuana.

The second item of note is the increase in marijuana use for people without a prescription for medical marijuana use and for people without a cannabis use disorder diagnosis. This data is an initial indicator that recreational use, as opposed to medical or disordered use, drives these upward trends.

The third item of note is the increase in use among adults age 65+ over the five years analyzed: additional research indicates that this increase is, indeed, related to the legalization of medical marijuana.

Marijuana Use in Teens

The adolescent population, as a whole, did not follow the general in-year quarterly trend seen in adults over the age of 18. Instead, in the adolescent population, past-month marijuana use:

• Increased from Q1 to Q2 for all five years
• Increased from Q2 to Q3 for all five years
• Peaked in Q3 for all five years
• Decreased in Q4 to Q1/Q2 levels for all five years

That makes sense to everyone who understands that, with some small regional variation, Q3 corresponds to summertime. As we all know, summer is the season when teenagers have more free time and fewer responsibilities, compared to the rest of the year. People who work in adolescent drug treatment – and parents of teens – know it’s also the time when teens are most likely to experiment with drugs.

Science Confirms Common Wisdom

During the summer, teens work jobs where they may meet people who use marijuana. They go away to camps and various sports or study programs where they may meet people who use marijuana. Teens who neither work jobs nor travel for summer programs have long days to fill – often on their own and unsupervised.

When we said, above, “People who work in adolescent drug treatment…and parents of teens know…” what we really meant was that “People who work in adolescent drug treatment and parents of teens have an abundance of anecdotal evidence to support the idea that teens are most likely to experiment with drugs during the summer.”

With this data, counselors, therapists, and parents now actually know they were right all along, at least where marijuana is concerned. The data indicates unequivocally that teen marijuana use peaks in the summertime.

For parents and for people who work in adolescent substance abuse treatment, this means they know when and where to focus mitigation and prevention strategies with regards to marijuana: in summertime, in the adolescent population.

Many have done this all along, based on experience and intuition. Now they have the data to back it up. They can leverage this data to encourage local community leaders, school administrators, and policymakers to increase vigilance during the summertime, and allocate resources to programs that keep teens busy and productive over the summer, and less likely to experiment with marijuana.