Alice G. Walton
Original Source: www.forbes.com
A new study in the journal Addiction lays out what the vast research on marijuana has revealed over the last 20 years, highlighting the drug’s adverse effects, both acute and chronic. Though researchers have been studying the effects of marijuana for decades, the science has really exploded just in the last 20 years, due in part to better study methods, and also spurred by the growing interest in legalization. The new study maps out exactly what marijuana does and does not do to the body and brain, both in the short and long terms. What’s clear is that marijuana has a number of adverse effects over years of use – in certain people, anyway. What’s not so clear is how policy should be informed by the science. But the researchers suggest that with increasing legalization should come increasing public awareness of the sometimes-serious effects of chronic use.
The acute effects aren’t so bad: No one has ever died from a natural marijuana overdose, the study found. (N.B. This is not true for synthetic marijuana, which can be very dangerous.) Driving while high on marijuana does seem to double the risk of a car crash, which is of course heightened if there is also alcohol in the system. Marijuana has been linked to low birth weight when it is used during pregnancy. Otherwise, acute effects mainly include anxiety, paranoia (especially among new users), dysphoria, cognitive impairment, and psychotic symptoms (especially in people with a family history of psychosis). These particular side effects seem to have risen over the last 20 years, which may be due to the fact that the THC content in marijuana has also risen over that time.
Over the long term, things get a little worse. It’s important to point out that in epidemiological studies, it can be very difficult to tease out whether cause and effect is actually at play, or whether there’s something else going on. But the authors have gone to great lengths to separate causation from correlation, combing the data for studies that point strongly to cause and effect. Here’s what they found:
- Marijuana can be addictive. But only for some people. About 10% of all users seem to develop dependence syndrome, and for those who start in adolescence, the number is more like 1 in 6. Withdrawal syndrome is also a real phenomenon, with depression, anxiety, insomnia, and appetite disturbance being the main symptoms, which can often be severe enough to have an effect on daily life.
- Marijuana use is linked to adverse cognitive effects. In particular, the drug is linked to reduced learning, memory, and attention. It hasn’t been entirely clear whether these effects persist after a person stops using the drug, but there’s some evidence that it does. One study found a reduction in IQ of 8 points in long-time users, the greatest decline being in people who’d started using as teenagers and continued daily into adulthood. For people who began in adulthood and eventually stopped using, a reduction in IQ was not seen a year later.
- Marijuana may change brain structure and function. There’s been an ongoing debate about whether marijuana actually changes the brain, but recent evidence has suggested that it is linked to changes in the hippocampus, amygdala, and prefrontal cortex. It’s unclear, however, how long these effects last, whether they’re linked to behavioral changes, and whether they reverse after a person stops using the drug.
- Regular use is linked to an increased risk of psychotic symptoms. That marijuana is linked to increased psychotic symptoms (e.g., delusions, hallucinations, disordered thinking) is fairly clear. But again, it’s been a chicken-and-egg problem, since it’s hard to show whether causation is at play, and which way the connection goes. However, it’s likely that the relationship actually goes both ways: Marijuana may lead to psychotic symptoms, and early psychotic symptoms may increase the likelihood that a person will smoke marijuana (particularly if there’s a family history of psychotic disorders).
- Marijuana is linked to lower educational attainment. When pot smoking begins in adolescence, people tend to go less far in school – but again, a causal relationship hasn’t been demonstrated.
- Marijuana may (or may not be) be a gateway drug. Regular teenage marijuana users are more likely to use other drugs in the future – but again, researchers don’t know whether the link is causal.
- Marijuana is probably – but modestly – linked to schizophrenia. The study found that marijuana is connected to a doubled risk of a schizophrenia diagnosis in the future. Many previous studies have suggested this connection, but, as always, showing causality is hard. The new study cites a number of well-executed studies that suggest a causal relationship between marijuana and schizophrenia. The authors estimate that marijuana use may double the risk of schizophrenia from 7 in 1000 non-users to 14 in 1000 marijuana users. On the upside, they point out that users who quit using the drug after a first psychotic episode have fewer psychotic symptoms and better social functioning moving forward, compared to people who have a psychotic episode but continue using.
- Marijuana may be linked to testicular cancer. Its connection to other forms of cancer is not very consistent, but there’s some evidence of an increased risk of testicular cancer in long-term marijuana users.
- Regular users may have cardiopulmonary issues. Regular marijuana users have a higher risk of developing chronic bronchitis. Marijuana “probably” increases the risk of heart attack in middle age, but it’s hard to know for sure, since many users also smoke cigarettes.
So the chronic effects of marijuana are becoming clearer, though some areas need more work. As the authors point out, none of this is to argue for or against the legalization of marijuana, which is gaining so much speed (and, of course, criticism) across the country. The authors are careful not to weigh in, except to say that if marijuana is legalized or decriminalized, it should be done with a number of safeties in place. As study author Wayne Hall, Director and Inaugural Chair at the Centre for Youth Substance Abuse Research at The University of Queensland, tells me, “Given that Colorado and Washington State have decided to legalise, the governments in these states should aim to regulate sales in ways that minimise the harms arising from use. This should certainly include informing users about the risks of use and doing what is possible to discourage uptake by adolescents.”
He stresses that methods to discourage new users, especially young ones, should be implemented by the government in as many ways as possible. “Regulation of cannabis,” says Hall, “should learn from experiences with alcohol and tobacco and use in limiting the number of heavy users by using taxation, limiting promotion of cannabis use and restricting where cannabis can be sold and by whom.” As more states debate the prospect of legalization, looking to the science may help them make some of the hard decisions. Or, of course, it could make the conversations that much more complex.
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