Long-Term Marijuana Dependence Linked to Problems at Midlife

A new landmark study by an international team of researchers reports that people who smoked cannabis four or more days of the week—for many consecutive years—experienced a wide range of social and economic problems at midlife.

The researchers of this longitudinal study followed children from age 3 to age 38. Their findings identified a correlation between the persistent, heavy use of cannabis and an increase of financial and work-related troubles, as well as difficulties with personal relationships.

The study was led by Magdalena Cerdá at the University of California, Davis, Health System along with Avshalom Caspi and Terrie Moffitt at Duke University. Other universities involved in this study included: the University of Otago, Dunedin, New Zealand; Institute of Psychiatry, King’s College, London; and Arizona State University.

The March 2016 study, "Persistent Cannabis Dependence and Alcohol Dependence Represent Risks for Midlife Economic and Social Problems: A Longitudinal Cohort Study," was published online today in the journal Clinical Psychological Science.

In a press release, Magdalena Cerdá, first author of the study and an epidemiologist at the UC Davis Violence Prevention Research Program, summed up the study saying, “Our research does not support arguments for or against cannabis legalization, but it does show that cannabis was not safe for the long-term users tracked in our study.”

For this study, the researchers assessed the frequency and duration of cannabis use among participants in the long-term Dunedin Multidisciplinary Health and Development Study from New Zealand.

This is a four-decade project managed by the University of Otago that has been following the development of a group of 1,037 children born in 1972-1973 from birth to age 38. The Dunedin study includes participants who represent the full range of socioeconomic status and health in the general population, each of whom has had regular follow-up exams since 3 years of age.

The authors of the recent study measured both persistence of cannabis dependence, as defined by the total number of research periods that a participant met criteria for cannabis dependence, and persistence of regular cannabis use as the total number of study periods out of five that a participant used cannabis for four or more days per week.

Eighteen percent of the original group were considered marijuana dependent in at least one wave of the study, and 15 percent fell into the regular cannabis use categories, in at least one wave of the study.

Approximately Six Million Americans Have Cannabis Use Disorders (CUD)

A few days ago, I wrote a Psychology Today blog post, “Cannabis Use Disorders Are Skyrocketing in the United States,” based on a new study which found that approximately 2.5 percent of American adults—nearly 6 million people—experienced marijuana use disorder in the past year. Of those who used marijuana, 6.3 percent met the latest DSM-5 diagnostic criteria for CUD at some point in their lives.

The study also reported that marijuana use disorder—which is often associated with other substance use disorders, behavioral problems, and disability—goes largely untreated for the majority of Americans. In fact, the researchers found that only about 7 percent of people with past-year marijuana use disorder received any marijuana-specific treatment, and only about 13 percent of people with lifetime marijuana use disorder receive treatment.

Cannabis use disorder was associated with other substance use disorders, affective disorders, anxiety, and personality disorders. For example, one of the findings of this study was that adults who use cannabis are five times more likely to develop an alcohol use disorder (AUD)—compared with adults who do not use marijuana.

In the comments to this blog post, one reader wrote, “Where are the risks? So, neglecting important personal and professional obligations is a risk?“ Coincidentally, the study released today answers this reader’s question directly. In a press release, Cerdá said,

"Our study found that regular cannabis users experienced downward social mobility and more financial problems such as troubles with debt and cash flow than those who did not report such persistent use. Regular long-term users also had more antisocial behaviors at work, such as stealing money or lying to get a job, and experienced more relationship problems, such as intimate partner violence and controlling abuse."

Persistent Cannabis Use Has Major Consequences for Individuals and Society

The latest comprehensive longitudinal research on cannabis presents a wide range of potentially confounding factors that haven’t been assessed comprehensively until now. These findings serve to raise our awareness about cannabis' long-term effects on individual users, plus the consequences that persistent cannabis use can have on families, communities, and national social welfare systems.

"These findings did not arise because cannabis users were prosecuted and had a criminal record," said Caspi, a psychologist with dual appointments at Duke University and the Institute of Psychiatry at King's College London. "Even among cannabis users who were never convicted for a cannabis offense, we found that persistent and regular cannabis use was linked to economic and social problems."

There's a common public conception that alcohol is infinitely more dangerous than cannabis, which may be true from a physiological standpoint. However, the researchers believe that marijuana isn’t necessarily 'safer' than alcohol in the long run.

Both heavy alcohol and cannabis use were similarly associated with declines in social class, antisocial behaviors in the workplace, and relationship problems. However, the authors found that people who had long-term cannabis dependency actually experienced more financial difficulties—such as paying for basic living expenses and food—than those who were alcohol dependent.

The authors measured social and economic problems at midlife using both self-reported questionnaires and public data. These included credit ratings, government social-welfare benefit records, and court documents. Socioeconomic mobility was measured by comparing social class in childhood (highest occupational status of either parent from the participant's birth to age 15) with social class in adulthood (most recent occupation of the participant at age 38).

Although this study only addressed the economic and social consequences of cannabis use, within the socioeconomic domain, the researchers found that persistent, heavy cannabis was, in fact, just as harmful as alcohol abuse.

"Alcohol is still a bigger problem than cannabis because alcohol use is more prevalent than cannabis use," Cerdá said. "But, as the legalization of cannabis increases around the world, the economic and social burden posed by regular cannabis use could increase as well."

Conclusions: Public Health and the Need for More Awareness of Cannabis' Risks

Discussing the potential benefits or dangers of marijuana use often triggers fierce reactions and leads to passionate debate. For the record, I don't have any strong personal opinions about the legalization of marijuana. My motivation for writing about the latest scientific research on the consequences of heavy marijuana use is to educate readers, so that every individual can make an informed personal decision about his or her marijuana use.

As I've stated previously, I smoked a ton of pot as a teenager—but after having a really 'bad trip' on psilocybin when I was seventeen—I stopped using drugs. The last time that I took a hit of pot, the cannabis was so potent that it gave me flashbacks to having a bad trip and made me feel like I was hallucinating. Therefore, I don't smoke weed, because it's an unpleasant experience that makes me feel paranoid. That said, I don't cast any moral judgment on people who choose to use, or not use, cannabis.

Given the monumental and historic shifts that are taking place in terms of cannabis policies, and the legalization of marijuana within regions of the United States, it's an important time to be pragmatic and look at empirical data to help each of us better understand the effects of cannabis on our well-being throughout the human lifespan.

According to a 2012 report from the Substance Abuse and Mental Health Services Administration, perceptions about the riskiness of cannabis have changed dramatically in recent years. For example, in the United States, the proportion of adolescents who perceive cannabis as risky has decreased to an all-time low of 45 percent.

As a public health advocate, I feel an obligation to educate people (especially teenagers) about the risks vs. rewards of long-term heavy marijuana use and the potential consequences of persistent cannabis use on your physical and mental health, as well as your socioeconomic security and stability.

The latest research shows that cannabis dependence can ultimately be associated with more financial difficulties than alcohol dependence. We live in an era when so many people's lives are dominated by economic insecurity, stress, and the pain that poverty causes. This study should serve as a reminder to individuals and policymakers that heavy cannabis use exacerbates economic strains and may not be as innocuous as previously believed.

Although the physical detriments of cannabis may not be as harmful as alcohol; heavy, long-term use of marijuana appears to be clinically proven to have the potential to create a destructive downward social and economic spiral in someone's life.

To read more on this topic, check out my Psychology Today blog posts,

• "Does Long-Term Cannabis Use Stifle Motivation?"
• "What Causes Economic Insecurity to Morph Into Physical Pain?"
• "Cannabis Use Disorders Are Skyrocketing in the United States"
• "Heroin Addiction Is Destroying the Lives of Young Americans"
• "Why Have Marijuana Use Disorders Doubled in the Past Decade?"
• "Heavy Marijuana Use Alters Teenage Brain Structure"
• "High Potency Marijuana Damages Cerebral Brain Connections"
• "Why Are Cannabis Users Susceptible to Memory Distortions?"
• "Consuming Legalized Marijuana Is Blindsiding Out-of-Towners"
• "Why Are So Many Middle-Aged White Americans Dying Young?"

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