What has research over the past two decades revealed about the adverse health effects of recreational cannabis use
Summary (1 min read)
Conclusions:
- The epidemiological literature in the past 20 years has confirmed that cannabis use increases the risk of accidents, can produce dependence and that there are consistent associations between regular cannabis use and poor psychosocial outcomes and mental health in adulthood that warrant efforts to discourage adolescent cannabis use.
- The effects sought by cannabis users -euphoria and increased sociability -seem to be primarily produced by delta-9-tetrahydrocannabinol (THC) [3] .
- THC content has also increased in the Netherlands and probably in other developed countries [5].
- Cannabis is usually smoked in a "joint" or with a water pipe (sometimes with tobacco added) because smoking is the most efficient way to achieve the desired psychoactive effects [3] .
- This pattern, when continued over years and decades, predicts increased risks of many of the adverse health effects attributed to cannabis that are reviewed below [6] .
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"What has research over the past two..." refers background or methods in this paper
...An attempted meta-analysis of similar studies [97] concluded that the designs of these studies and measures used were too varied to quantify risk meaningfully, and most of the studies had not excluded reverse causation or controlled adequately for confounding....
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...A meta-analysis of these studies [97] reported a modest association between cannabis use and depressive disorders (OR = 1....
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1,824 citations
"What has research over the past two..." refers background in this paper
...Our best estimate is that the risk of developing a psychosis doubles from approximately 7 in 1000 in nonusers [102] to 14 in 1000 among regular cannabis users....
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1,315 citations
"What has research over the past two..." refers result in this paper
...The bestdesigned and most informative of these studies have been two New Zealand birth cohort studies whose members lived through a historical period during which a large proportion used cannabis during adolescence and young adulthood; sufficient numbers of these had used cannabis often enough, and for long enough, to provide information about the adverse effects of regular and sustained cannabis use....
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...A recent meta-analysis of three Australian and New Zealand longitudinal studies [72] showed that the earlier the age of first cannabis use, the lower the chances of completing school and undertaking postsecondary training....
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...For example, a New Zealand case–control study [116] of suicide attempts that resulted in hospitalization found that 16% of the 302 suicide attempters had a cannabis disorder compared with 2% of 1028 community controls....
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...This study assessed changes in IQ between age 13 (before cannabis was used) and at age 38 in 1037 New Zealanders born in 1972 or 1973 [63]....
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...A New Zealand case–control study of lung cancer in 79 adults under the age of 55 years and 324 community controls [145] found a dose–response relationship between frequency of cannabis use and lung cancer risk....
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1,239 citations
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Frequently Asked Questions (10)
Q2. How many times did a person who tried cannabis use a diagnosis of schizophrenia?
After statistical adjustment for a personal history of psychiatric disorder by age 18 and parental divorce, those who had used cannabis 10 or more times by age 18 were 2.3 times more likely to receive a diagnosis of schizophrenia than those who had not used cannabis.
Q3. What is the consistent finding in epidemiological studies of drug use in young adults?
The order of involvement with cannabis and other illicit drugs, and the increased likelihood of using other illicit drugs, are the most consistent findings in epidemiological studies of drug use in young adults.
Q4. What is the effect of cannabis on the risk of a car crash?
In summary, the epidemiological and laboratory evidence on the acute effects of cannabis strongly suggests that cannabis users who drive while intoxicated increase their risk of motor vehicle crashes 2-3 times [20] as against 6-15 times for comparable intoxicating doses of alcohol.
Q5. How much of the risk of failing to complete high school or post-secondary training was ?
The authors estimated that early use of cannabis contributed to 17% of the risk of failing to complete high school or post-secondary training.
Q6. How many times did conscripts who tried cannabis have schizophrenia?
Conscripts who had tried cannabis by age 18 were 2.4 times more likely to be diagnosed with schizophrenia over the next 15 years than those who had not [91].
Q7. What was the main reason for the lack of studies that reported increased rates of birth defects?
It was also difficult to interpret the few studies that did reported increased rates of birth defects (e.g [22]) because cannabis users were more likely to smoke tobacco, and use alcohol and other illicit drugs during pregnancy [23].
Q8. How many low income women have reported lower scores on the Stanford-Binet Intelligence?
In the past 20 years another cohort of low income women with higher rates of regular cannabis use [31] has reported lower scores on memory and verbal scales of the Stanford-Binet Intelligence Scale at age 3 in children born to 655 low income women (half African-American and half Caucasian) in Pittsburgh between 1990 and 1995.
Q9. What did the authors conclude that the studies were too varied to quantify risk?
An attempted meta-analysis of similar studies [97] concluded that the designs of these studies and measures used were too varied to meaningfully quantify risk and most of the studies had not excluded reverse causation or adequately controlled for confounding.
Q10. What is the reason for the decline in cognitive performance of cannabis users?
Cognitive impairmentIn 1993 case-control studies reported that regular cannabis users had poorer cognitive performance than non-cannabis-using controls but it was unclear whether this was because cannabis use impaired cognitive performance, persons with poorer cognitive functioning were more likely to become regular cannabis users, or some combination of the two [9].