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Is Marijuana Addictive?
Well, yes. But it’s complicated.
The idea that pot is not addictive is widespread. A global survey of 55,000 cannabis users last year found that while 75% believe messages around the health risks of marijuana — from driving under the influence to forgetfulness, as well as harmful chemicals in the smoke — only 64% believe the fact that some people who try it become addicted. Yet health experts and scientists agree marijuana is addictive, though less so than, say, heroin. And as cannabis potency soars, some experts worry that the addictive potential is rising, especially for the under-25 set whose brains are still developing.
“Definitely, yes,” cannabis is addictive, says Ruben Baler, a health scientist at the science-policy branch of the National Institute on Drug Abuse (NIDA). “About 10% of people who use marijuana run the risk of addiction,” Baler says. “The risk goes up if you use it frequently.”
Furthermore, according to a NIDA statement, “data suggest that 30% of those who use marijuana may have some degree of ‘marijuana use disorder,’” a term recently rolled into the pot lexicon in an as yet confusing attempt to recognize a spectrum of use from relatively harmless to harmful, and to snuff out the stigma of addiction.
Your brain on pot
A brain-imaging study last year found the brain’s neural circuitry is altered in young adults with cannabis dependence, especially for those who start in adolescence. “People with heavy cannabis use had abnormally high connectivity in brain regions important for reward processing and habit formation,” wrote the researchers, led by Peter Manza at the National Institute on Alcohol Abuse and Alcoholism. The findings were detailed in the journal Biological Psychiatry: Cognitive Neuroscience and Neuroimaging.
All human addictions point back to dopamine, a chemical that transmits information between the brain’s neurons. Dopamine regulates many functions, from attention and learning to motor skills and emotions. In particular, dopamine is largely responsible for the sense of pleasure, that human frailty behind many motivations and all addictions. But dopamine doesn’t act alone. There’s serotonin (another feel-good chemical), adrenaline, and others.
“Whether you are watching a movie, having sex or eating a slice of pizza, neurotransmitters are flowing back and forth, helping you make sense of the experience,” Baler explains.
All this is governed by the endocannabinoid system, a set of molecules in the brain and throughout the body that act as an all-powerful puppet master for the other neurotransmitting systems. It employs its own neurotransmitters and also enzymes that make or can destroy others. “It dials things up or down to modulate the effect and balance various system in the brain,” Baler says. “It is a major translator of every experience you go through.”
But the endocannabinoid system has its kryptonite: delta-9-tetrahydrocannabinol, or THC.
THC, a cannabinoid produced in the resin of leaves and buds primarily from the female marijuana plant, is a master of disguise. It mimics the brain’s endocannabinoids and locks onto natural cannabinoid receptors.
“THC hijacks the system,” Baler says. The stoned mind is flooded with dopamine, no longer able to properly processes emotions, particularly pleasure. The result for most people, of course, is a good feeling. “Addiction happens when a substance or activity causes the dopamine system to make something pleasurable a habit that becomes stronger and stronger over time,” he says.
When cannabis use starts young, the hijacking alters the very structure of the brain’s developing hardware and inserts bad code into its software as it’s being written, potentially setting kids up for addiction problems down the road.
What, exactly, is “addiction”?
Official definitions, especially as they relate to marijuana, are vague and varying. Much of the confusion stems from a move over the past six years to strip the word “addiction” from scientific texts in favor of “substance use disorder.” NIDA, part of the National Institutes of Health (NIH), still sprinkles “addiction” liberally in its explanation of marijuana risks, while an NIH web page discussing “marijuana use disorder” completely avoids mentioning “addiction” in relation to marijuana. Meanwhile, “severe substance use disorder” and “addiction” are used interchangeably by the American Psychiatric Association.
Part of the motivation has to do with the meaning of “addiction” becoming diluted. In addition to describing chemically induced dependencies, “Addiction is a more general term, describing behaviors like sex, shopping and gambling,” as well as the internet, video games, and phones, Baler explains. The linguistic pivot also includes a move away from “disease” in favor of “disorder” and dropping “abuse” in favor of varying degrees of “use” — all efforts to destigmatize drug use.
The logic: Many people “use” substances that can be harmful, but that use may not necessarily interfere with life. “When that use becomes pathological, it becomes ‘substance use disorder,’” Baler says.
“Your life is not going to be upended by that infrequent use. If you smoke every day… the risk of it impacting your life shoots up.”
This emerging definition of substance use disorder was introduced in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, or DSM-5, published in 2013 and representing decades of evolved scientific thinking. DSM-5 was developed by the APA in cooperation with NIDA and other U.S. and global health agencies.
DSM-5 replaced “substance abuse” and “substance dependence” with one category: “substance use disorder.” It has three flavors: mild, moderate and severe. According to the definition, experiencing any two of these 11 criteria constitutes what experts used to call addiction:
Interpreting the DSM-5 for cannabis is even hazier. NIDA, interpreting DSM-5, puts it this way: “Marijuana use can lead to the development of problem use, known as a marijuana use disorder, which takes the form of addiction in severe cases,” suggesting mild and moderate use disorders don’t signify addiction. By the new definition, it remains unclear exactly how many people have marijuana use disorder and how many suffer outright addiction.
A 2015 study led by Deborah Hasin, a professor of psychology and epidemiology at Columbia University, found that nearly 30% of marijuana users “experienced a marijuana use disorder of abuse or dependence.” The finding is based on the DSM-5 definitions, “which are somewhat more inclusive than the way people ordinarily think of ‘addiction,’” Hasin says.
Risk factors for addiction
A person suffering from addiction, regardless of the substance, uses the substance compulsively, to the point that it takes over their lives, at least in part. They have “distorted thinking, behavior and body functions,” according to the American Psychiatric Association. “Changes in the brain’s wiring are what cause people to have intense cravings for the drug and make it hard to stop using the drug.” Over time, a person builds tolerance and needs more.
Marijuana is the most commonly used illicit drug in the United States, yet as with alcohol, not everyone who tries pot will develop a lifelong, destructive habit. Men are more likely than women to get hooked, as are people who smoke tobacco. Other factors that make a person more prone to cannabis addiction, according to several experts:
- Younger starting age
- Frequency of use
- Depression or other underlying psychiatric illness
- Potency of the pot
And as with alcohol, moderate marijuana consumption by most people 25 and older is seen by many experts as, well, no big deal.
“If you, as an adult, smoke a joint with relatively low potency during the weekends… you’ll probably be okay, unless you suffer from a mental illness or another environmental risk factor,” says Baler, the NIDA scientist. “Your life is not going to be upended by that infrequent use. If you smoke every day… the risk of it impacting your life shoots up.”
The zeitgeist of cannabis
Getting heavy marijuana users to recognize they have a problem can be difficult.
“People who are addicted are characteristically slow to recognize their own addiction, regardless of the substance that’s the issue, because of denial, because of impaired cognitive functioning, or whatever other factors are causing this,” Hasin says. “However, recognizing a cannabis use disorder or cannabis ‘addiction’ is even more problematic than other substances, because the zeitgeist right now is that cannabis is harmless.”
A classic sign of addiction is withdrawals, and marijuana withdrawal syndrome is included in DSM-5. Hasin and colleagues reviewed data from a nationwide series of in-home surveys from 2012–13 that included 1,527 frequent cannabis users 18 and older. Among them, 12% said they experienced cannabis withdrawal syndrome. Here were the most commonly reported symptoms, which Hasin says are also common to depressive disorders:
- Nervousness or anxiety: 76%
- Hostility: 72%
- Sleep difficulty: 68%
- Depressed mood: 59%
Common physical symptoms included headaches, shakiness or tremors and sweating, the researchers reported in the journal Drug and Alcohol Dependence.
“Cannabis withdrawal has been well-characterized in laboratory, clinical and epidemiologic studies, so there is solid evidence about this,” Hasin says. Upon stopping, heavy users may not realize their symptoms are due to withdrawal, so they use more, feel better, “and then think the cannabis is helping them.”
Cannabis withdrawal syndrome is “absolutely real,” says Edwin Salsitz, an associate clinical professor of psychiatry and a specialist in addiction medicine at Mount Sinai Icahn School of Medicine. He says the cycle of addiction is compounded by the fact that today’s cannabis is not your grandfather’s weed.
“A lot of Baby Boomers are remembering what it was like to smoke marijuana in the ’60s, when the THC level was significantly lower,” Salsitz explains. What’s more, “Mostly young adults were smoking marijuana in the ’60s and ’70s, not young kids. And now, unfortunately, young kids are smoking as well. It might not have been as addictive to a 25-year-old hippie, but it is more addictive to a teenager.”
Increasingly powerful weed
While cannabis has more than 500 different compounds, including more than 100 cannabinoids whose possible effects aren’t well studied, potency is generally measured by the concentration of THC.
The potency of cannabis seized on its way to illegal sales in the United States rose consistently from 4% in 1995 to about 12% in 2014, according to a study in the journal Biological Psychiatry. The reason is simple: The rise in sensimilla marijuana.
Marijuana comes in two basic varieties: regular, and sensimilla, which is derived from an unfertilized female marijuana plant unable to produce seeds. Instead, it puts all its energy into creating new buds with higher concentrations of THC, making sensimilla more potent. The number of seized regular marijuana samples declined from nearly 100% in 1995 to about 20% in 2014, while sensimilla rose from near zero to around 80%.
Meanwhile, in England and Wales, cannabis use had been declining through 2015, but the demand for cannabis addiction treatment was on the rise, according to Tom Freeman at University College London. He and a colleague looked into why, finding a “huge variation” in cannabis potency in the illicit and legal markets. And among young marijuana users, they found that 43% of those who preferred high-potency varieties were dependent on cannabis compared to 22% of those who went for the milder stuff.
“The illicit cannabis market is dominated by high-potency cannabis containing high THC,” Freeman says. “Our findings suggest that people who prefer this type of cannabis are around twice as likely to show problematic use.” The results were published in the journal Psychological Medicine.
THC concentrations can skyrocket in solutions that can be added to drinks, or in dabbing. In dabbing, people inhale vapors from a cannabis concentrate, with names like hash oil and waxy budder, by bong or vaping. Dabs can be four times as concentrated as the cannabis in a typical high-grade joint, according to the U.S. Drug Enforcement Administration.
Higher doses have a greater effect on a neuron when THC binds to its cannabinoid receptor, as well as “what happens to the user’s feelings, perceptions, emotions, desire to repeat the experience,” Baler says.
However, while cannabis use among U.S. adults has risen over the past two decades, the percentage of users who have marijuana use disorder has not changed, at least according to Hasin’s 2015 study. Yet with teen use of vape products soaring in recent years, it remains to be seen what effects the higher potency cannabis might have.
Vulnerable young brains
Marijuana use among teens peaked in the late 1990s, declined through the mid-2000s, and has since leveled off. Still, it is used daily by nearly 5.8% of high-school seniors in the United States and 3.4% of 10th graders, according to the National Institute on Drug Abuse. Nearly a quarter of seniors say they’ve tried it in the past month, and 44% during their lives. Nearly 14% of eighth graders have tried pot. Use by teens and young adults worries health experts, because THC is much more damaging to developing brains, and its addictive power is far greater.
Think of the brain as the most complex computer known, and the endocannabinoid system as head of programming. The brain’s hardware and software aren’t fully built and written until around age 25. Until then, every experience — from food and exercise to love and abuse — creates lasting connections between neurons, along with thick bundles of fiber connecting different brain regions. The mind’s memory cards and processor chips are soldered onto the motherboard, an operating system is designed, and apps are created for everything from decision-making to impulse control.
A study published last year in the American Journal of Psychiatry involving 3,826 Canadian adolescents across four years linked marijuana use to poorer memory, reasoning skills and ability to control inhibitions, especially when the kids started at younger ages. “Of particular concern was the finding that cannabis use was associated with lasting effects on a measure of inhibitory control, which is a risk factor for other addictive behaviors, and might explain why early-onset cannabis use is a risk factor for other addictions,” says study team member Patricia Conrod at the University of Montreal.
“It’s a vulnerable period,” Baler says. “You’re writing the programs for the rest of your life. If you interfere with programming, you run the risk of incorporating errors into the program.” THC doesn’t just hack the brain by inserting a feel-good script, it puts youth “exponentially higher” risk for addiction, he says.
It’s important to note, however, that the number of children using marijuana in the United States remained flat from 2008 through 2018, according to NIDA. Even in Colorado, where cannabis is widely available, use among youth has not risen since legalization, according to the state’s Department of Public Health and the Environment. Whether the rate of addiction among young users has changed remains an open question.
The National Organization for the Reform of Marijuana Laws (NORML), a group that advocates for legalization, acknowledges the dependency potential of marijuana and the additional risks for youth, though it emphasizes the lower “dependence liability” compared to either alcohol or tobacco, says Paul Armentano, the organization’s deputy director.