People
who drive under the influence of marijuana double their risk of being in a car
crash, and about one in 10 daily marijuana users becomes dependent on the drug,
according to a new review.
Marijuana
use has become increasingly prevalent over the years, and the review of
marijuana studies summarizes what researchers have learned about the drug's
effects on human health and general well-being over the past two decades.
In
the review, author Wayne Hall, a professor and director of the Center for Youth
Substance Abuse Research at the University of Queensland in Australia, examined
scientific evidence on
marijuana's health effects between 1993 and 2013.
He
found that adolescents who use cannabis regularly are about twice as likely as
their nonuser peers to drop out of school, as well as experience cognitive
impairment and psychoses as adults. Moreover, studies have also linked regular
cannabis use in adolescence with the use of other illicit drugs, according to
the review, published today (Oct. 6) in the journal Addiction.
Researchers
in the studies still debated whether regular marijuana use might actually lead
to the use of other drugs, Hall wrote in the study. However, he pointed to
longer-term studies and studies of twins in which one used marijuana and the
other did not as particularly strong evidence that regular cannabis use may
lead to the use of other illicit drugs. [Marijuana vs. Alcohol: Which Is Worse
for Your Health?]
The
risk of a person suffering a fatal overdose from marijuana is "extremely
small," and there are no reports of fatal overdoses in the scientific
literature, according to the review. However, there have been case reports of
deaths from heart problems in seemingly otherwise healthy young men after they
smoked marijuana, the report said.
"The
perception that cannabis is a safe drug is a mistaken reaction to a past
history of exaggeration of its health risks," Hall told Live Science.
However,
he added that marijuana "is not as harmful as other illicit drugs such as
amphetamine, cocaine and heroin, with which it is classified under the law in
many countries, including the USA."
The risks of using
marijuana
Marijuana
use carries some of the same risks as alcohol use, such as an increased risk of
accidents, dependence and psychosis, he said.
It's
likely that middle-age people who smoke marijuana regularly are at an increased
risk of experiencing a heart attack, according to the report. However, the
drug's "effects on respiratory function and respiratory cancer remain
unclear, because most cannabis smokers have smoked or still smoke
tobacco," Hall wrote in the review.
Regular
cannabis users also double their risk of experiencing psychotic symptoms and
disorders such as disordered thinking, hallucinations and delusions — from
about seven in 1,000 cases among nonusers to 14 in 1,000 among regular
marijuana users, the review said. And, in a study of more than 50,000 young men
in Sweden, those who had used marijuana 10 or more times by age 18 were about
two times more likely to be diagnosed with schizophrenia within the next 15
years than those who had not used the drug.
Critics
argue that other variables besides marijuana use may be at work in the
increased risk of mental health problems, and that it's possible that people
with mental health problems are more likely to use marijuana to begin with,
Hall wrote in the review.
However,
other studies have since attempted to sort out the findings, he wrote, citing a
27-year follow-up of the Swedish cohort, in which researchers found "a
dose–response relationship between frequency of cannabis use at age 18 and risk
of schizophrenia during the whole follow-up period."
In
the same study, the investigators estimated that 13 percent of schizophrenia
cases diagnosed in the study "could be averted if all cannabis use had
been prevented in the cohort," Hall reported.
As
for the effects of cannabis use in pregnant women, the drug may slightly reduce
the birth weight of the baby, according to the review.
More THC?
The
effects of euphoria that cannabis users seek from the drug come primarily from
its psychoactive ingredient, called delta-9-tetrahydrocannabinol, better known
as THC, Hall wrote in the review. During the past 30 years, the THC content of
marijuana in the United States has jumped from less than 2 percent in 1980 to
8.5 percent in 2006.
The
THC content of the drug has also likely increased in other developed countries,
Hall wrote in the report.
It
is not clear, however, whether increased THC content may have an effect on
users' health, the report said. [The Drug Talk: 7 New Tips for Today's Parents]
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