Marijuana and Your Health: What 20
Years of Research Reveals.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.
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. 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. Some argue that there would be no increase in harm, if users
adjusted their doses of the drug and used less of the more potent cannabis
products to get the same psychological effects they seek, Hall said.
However, "the limited evidence suggests that users do
not completely adjust dose for potency, and so probably get larger doses of THC
than used to be the case," Hall said.
Studies on the use of alcohol — and, to a lesser extent,
other drugs such as opioids — have also shown that more potent forms of these
substances increase users' level of intoxication, as well as their risk of
accidents and developing dependence, he added.
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