Study: Adolescent marijuana use leaves lasting mental deficits
The persistent, dependent use of marijuana before age 18 has been shown to cause lasting harm to a person's intelligence, attention and memory, according to an international research team.
Among a long-range study cohort of more than 1,000 New Zealanders, individuals who started using cannabis in adolescence and used it for years afterward showed an average decline in IQ of 8 points when their age 13 and age 38 IQ tests were compared. Quitting pot did not appear to reverse the loss either, said lead researcher Madeline Meier, a post-doctoral researcher at Duke University. The results appear online Aug. 27 in PNAS.
The key variable in this is the age of onset for marijuana use and the brain's development, Meier said. Study subjects who didn't take up pot until they were adults with fully-formed brains did not show similar mental declines. Before age 18, however, the brain is still being organized and remodeled to become more efficient, she said, and may be more vulnerable to damage from drugs.
"Marijuana is not harmless, particularly for adolescents," said Meier, who produced this finding from the long term Dunedin Multidisciplinary Health and Development Study. The study has followed a group of 1,037 children born in 1972-73 in Dunedin, New Zealand from birth to age 38 and is led by Terrie Moffitt and Avshalom Caspi, psychologists who hold dual appointments at Duke and the Institute of Psychiatry at King's College London.
About 5 percent of the study group were considered marijuana-dependent, or were using more than once a week before age 18. A dependent user is one who keeps using despite significant health, social or family problems.
At age 38, all of the study participants were given a battery of psychological tests to assess memory, processing speed, reasoning and visual processing. The people who used pot persistently as teens scored significantly worse on most of the tests. Friends and relatives routinely interviewed as part of the study were more likely to report that the persistent cannabis users had attention and memory problems such as losing focus and forgetting to do tasks.
The decline in IQ among persistent cannabis users could not be explained by alcohol or other drug use or by having less education, Moffitt said.
While 8 IQ points may not sound like a lot on a scale where 100 is the mean, a loss from an IQ of 100 to 92 represents a drop from being in the 50th percentile to being in the 29th, Meier said. Higher IQ correlates with higher education and income, better health and a longer life, she said. "Somebody who loses 8 IQ points as an adolescent may be disadvantaged compared to their same-age peers for years to come," Meier said.
Laurence Steinberg, a Temple University psychologist who was not involved in the research, said this study is among the first to distinguish between cognitive problems the person might have had before taking up marijuana, and those that were apparently caused by the drug. This is consistent with what has been found in animal studies, Steinberg added, but it has been difficult to measure in humans.
Animal studies involving nicotine, alcohol and cocaine have shown that chronic exposures before the brain is fully developed can lead to more dependence and long-term changes in the brain. "This study points to adolescence as a time of heightened vulnerability," Steinberg said. "The findings are pretty clear that it is not simply chronic use that causes deficits, but chronic use with adolescent onset."
What isn't possible to know from this study is what a safer age for persistent use might be, or what dosage level causes the damage, Meier said. After many years of decline among US teens, daily marijuana use has been seen to increase slightly in the last few years, she added. Last year, for the first time, US teens were more likely to be smoking pot than tobacco.
"The simple message is that substance use is not healthy for kids," Avshalom Caspi said via email from London. "That's true for tobacco, alcohol, and apparently for cannabis."
More information: "Persistent Cannabis Users Show Neuropsychological Decline From Childhood to Midlife," Madeline H. Meier, Avshalom Caspi, et al. Proceedings of the National Academy of Sciences, Online Early Edition, Monday, Aug. 27, 2012.
Journal reference: Proceedings of the National Academy of Sciences
Provided by Duke University
- High childhood IQ linked to subsequent illicit drug use Nov 15, 2011 | not rated yet | 0
- Early exposure to drugs, alcohol creates lifetime of health risk Oct 16, 2008 | not rated yet | 0
- Lower childhood IQ associated with higher risk of adult mental disorders Dec 01, 2008 | not rated yet | 0
- Heavy marijuana use may damage developing brain in teens, young adults Feb 02, 2009 | not rated yet | 0
- Team finds childhood clues to adult schizophrenia Jan 21, 2010 | not rated yet | 0
- Motion perception revisited: High Phi effect challenges established motion perception assumptions Apr 23, 2013 | 3 / 5 (2) | 2
- Anything you can do I can do better: Neuromolecular foundations of the superiority illusion (Update) Apr 02, 2013 | 4.5 / 5 (11) | 5
- The visual system as economist: Neural resource allocation in visual adaptation Mar 30, 2013 | 5 / 5 (2) | 9
- Separate lives: Neuronal and organismal lifespans decoupled Mar 27, 2013 | 4.9 / 5 (8) | 0
- Sizing things up: The evolutionary neurobiology of scale invariance Feb 28, 2013 | 4.8 / 5 (10) | 14
Pressure-volume curve: Elastic Recoil Pressure don't make sense
10 hours ago From pressure-volume curve of the lung and chest wall (attached photo), I don't understand why would the elastic recoil pressure of the lung is...
If you became brain-dead, would you want them to pull the plug?
May 17, 2013 I'd want the rest of me to stay alive. Sure it's a lousy way to live but it beats being all-the-way dead. Maybe if I make it 20 years they'll...
MRI bill question
May 15, 2013 Dear PFers, The hospital gave us a $12k bill for one MRI (head with contrast). The people I talked to at the hospital tell me that they do not...
Ratio of Hydrogen of Oxygen in Dessicated Animal Protein
May 13, 2013 As an experiment, for the past few months I've been consuming at least one portion of Jell-O or unflavored Knox gelatin per day. I'm 64, in very...
Alcohol and acetaminophen
May 13, 2013 Edit: sorry for the typo in the title , can't edit I looked around on google quite a bit and it's very hard to find precise information on the...
Marie Curie's leukemia
May 13, 2013 Does anyone know what might be the cause of Marie Curie's cancer
- More from Physics Forums - Medical Sciences
More news stories
The latest makeover to a massive psychiatric tome honored by some, reviled by others and even called the "Bible" of mental disorders is being released Saturday with a host of new changes.
Psychology & Psychiatry 44 minutes ago | not rated yet | 0
(HealthDay)—Most Medicare beneficiaries treated in inpatient psychiatric facilities (IPFs) exhibit characteristics associated with hospital readmission, according to a report prepared for the National Association ...
Psychology & Psychiatry 22 hours ago | not rated yet | 0
Skydivers show the same level of physical stress before every jump whether a first-timer or experienced jumper, say Northumbria researchers.
Psychology & Psychiatry 23 hours ago | not rated yet | 0 |
Children of depressed parents pick up on their parents' sadness—whether mom or dad realizes their mood or not.
Psychology & Psychiatry May 17, 2013 | 4.5 / 5 (2) | 1 |
(HealthDay)—As many as one in five American children under the age of 17 has a diagnosable mental disorder in a given year, according to a new federal report.
Psychology & Psychiatry May 16, 2013 | 2.2 / 5 (5) | 1 |
A new case of the deadly coronavirus has been detected in Saudi Arabia where 15 people have already died after contracting it, the health ministry announced on Saturday on its Internet website.
1 hour ago | not rated yet | 0
An increasing number of U.S. children are experiencing gastrointestinal issues that require interventions to resolve, according to research presented at Digestive Disease Week (DDW).
3 hours ago | not rated yet | 0 |
A ground-breaking advance in colonoscopy technology signals the future of colorectal care, according to research presented today at Digestive Disease Week(DDW). Additional research focuses on optimizing the minimal withdrawal ...
3 hours ago | 5 / 5 (1) | 0
Big names in medicine are set to give an upbeat assessment of the war on AIDS on Tuesday, 30 years after French researchers identified the virus that causes the disease.
11 hours ago | 5 / 5 (1) | 0
For combat veterans suffering from post-traumatic stress disorder, 'fear circuitry' in the brain never rests
Chronic trauma can inflict lasting damage to brain regions associated with fear and anxiety. Previous imaging studies of people with post-traumatic stress disorder, or PTSD, have shown that these brain regions can over-or ...
12 hours ago | 5 / 5 (1) | 0 |
(Medical Xpress)—What if the quality of your work depends more on your focus on the piano keys or canvas or laptop than your musical or painting or computing skills? If target users can be convinced, they ...
May 17, 2013 | 3.7 / 5 (3) | 0 |