CLAIM ONE: 鈥淐ritical skills related to attention, memory and learning are
impaired among heavy users of marijuana . . .鈥�
MOST people think of marijuana users as dreamers with the attention span of a
gnat and no memory worth the name. Wrong. The picture emerging from psychology
labs is that there is at most a kernel of truth in this stereotype, while some
studies find no evidence of even subtle mental impairment in heavy users. And
even those that do are open to a range of interpretations鈥攏ot necessarily
worrying to marijuana users.
Take the latest findings on which the above claim is based. Harrison Pope and
his team at Harvard University compared 65 college students who smoked marijuana
daily with a control group of students who smoked it most every other month.
After a drug-free day, the subjects completed a range of standard mental tests.
Mostly, differences between the two groups were slight. When it came to
remembering lists of words, for example, the heavy users recalled about 1 in 10
fewer words than the light users.
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But in one test the heavy users underperformed more noticeably. The test
involved watching and mimicking the simple rules used by an experimenter to
match cards with coloured shapes on them, and then adapting whenever the rule
changed. Students who rarely smoked marijuana mistakenly carried on with the old
sorting rule on about 5 out of 100 occasions, while heavy users made about 8
mistakes. Pope takes this seriously. 鈥淚n the real world,鈥� he says, 鈥減eople have
to deal all the time with situations in which rules are changing . . .鈥�
Fine. But over the years, much stronger claims have surfaced: heavy marijuana
users do badly at work or school, are more likely to be delinquent and develop
psychiatric problems, or have abnormal brain waves. Time and again, however,
such studies encounter the same objection: are the problems caused by smoking
marijuana, or is it just that people with problems are more likely to end up
using marijuana heavily?
In the case of delinquency, schizophrenia and mental illnesses, the balance
of the evidence points to the second explanation. Marijuana doesn鈥檛 cause the
problems, although it may make them worse. Some schizophrenics, for example, are
drawn to the drug because it eases their sense of alienation. And most
researchers now accept that the evidence linking marijuana to abnormal brain
waves vanishes when people with psychiatric problems, illnesses or a history of
general drug abuse are excluded from studies.
But what about subtler problems like the card sorting deficiencies? After
all, it might just be that smart college students tend to smoke lightly while
others smoke heavily. In which case the card sorting results may have little to
do with marijuana.
Here opinions diverge. Pope believes the deficiency does have something to
with marijuana because his team controlled for such obvious things as IQ
differences, psychiatric histories and heavy use of other drugs. But others are
not convinced. What worries some critics is that in this study, as in others,
the women drug users did so much better than the men in most tests.
Deviant males
鈥淚 know of no reason why there should be a gender difference in cognitive
response to cannabis,鈥� says John Morgan, a pharmacologist at the City University
of New York Medical School and co-author of a controversial new book advocating
decriminalisation, Marijuana Myths Marijuana Facts. Morgan believes the
reason the males underperform in such studies is that they are 鈥渄eviant鈥� in
subtle ways that escape the researchers鈥� notice.
And what if the poor test results do turn out to be linked to marijuana? It
doesn鈥檛 automatically follow that heavy marijuana use is causing long-lasting
brain damage. One possibility is that, deprived of their favourite drug for a
day, heavy users suffer withdrawal symptoms or become so grumpy and distracted
that they do badly in tests. Another is that a single drug-free day is not long
enough for the effect of their last smoke to have disappeared. The Harvard
team鈥檚 follow-on experiments, in which marijuana users are being tested over a
28-day 鈥渄ry鈥� period, should provide answers.
Other research suggests that evidence of dramatic mental decline is unlikely
to be found, even as a result of long-term heavy use. Over the past 25 years,
Jack Fletcher at the University of Texas in Houston and his colleagues have been
visiting Costa Rica to test the mental skills of very heavy users. Although some
of them have smoked 10 joints a day for more than 30 years, their ability to
learn and remember lists of words is only mildly impaired
(see figure). And even
when struggling with more demanding tasks, such as recalling information while
pressing a tapper as fast as possible, their scores fall well within the normal
range.FIG-21224701.jpg
鈥淭he effects are subtle and subclinical,鈥� says Brian Page, an anthropologist
from the University of Miami, who was involved in the study. 鈥淎lthough they
could be bad for somebody who鈥檚 trying to be an arbitrage trader or Wall Street
lawyer.鈥� And, Page adds: 鈥淧eople who sell bicycles had better not ride while
under the influence.鈥�
Or at any rate common sense suggests they should not. The verdict from
research into the impact of marijuana on road safety skills is less clear. In
Britain as many as 1 in 10 motorists involved in serious accidents test positive
for cannabis. And figures as high as 37 per cent have emerged from studies in
urban areas of the US. However, many of these drivers also test positive for
alcohol, and even the cases involving just cannabis cannot be equated with
people driving under the influence because the drug lingers so long in the
body.
In driving simulators, marijuana does impair visual skills and mental
dexterity. But studies of actual driving show that even high doses of marijuana
have less impact than alcohol, perhaps because smoking it doesn鈥檛 usually make
people so reckless. In one study, low doses of marijuana made drivers more
cautious.
The same broad message is likely to be true for the subtler, longer-lasting
effects of marijuana on the brain. Researchers like Pope and Morgan may look at
the data very differently, but they agree about one thing: heavy boozing is
worse for your neurons than dope.
CLAIM TWO: 鈥淢ore than 120 000 people in the US seek treatment each year for
their marijuana addiction . . .鈥�
AFTER years of decline, marijuana use among teenagers is now climbing rapidly
in almost every industrialised nation. Will this create a generation of cannabis
addicts?
The middle classes who enjoy a smoke once or twice a week may laugh at the
idea. But doctors who treat the minority of users who have lost control take it
more seriously. The pragmatic question is how big is this minority and would it
expand if the drug was decriminalised or even legalised? The experience of the
Netherlands
(see p 30)
suggests the answer to the second question is 鈥渘o鈥�. The first question is tougher.
At the very least, NIDA鈥檚 figure of 120 000 cannot be taken seriously. It
includes people who are arrested for cannabis offences and then given the chance
of going into treatment as an alternative to prosecution, as well as workers who
test positive for cannabis in random urine tests and opt for rehabilitation
rather than being fired. The figures don鈥檛 tell us how many people really get
hooked.
At Columbia University in New York, addiction epidemiologist Denise Kandel
has been taking a different tack. She has been analysing data collected every
year in the US National Household Survey on Drug Abuse. And she concludes that
subtle symptoms of dependence are more widespread among teenage users than
previously thought.
Shocking statistic
About 15 per cent of teenagers who smoke marijuana report three or more
鈥渟ymptoms鈥� of dependence from a list of six possible symptoms. They range from
鈥渇eeling dependent鈥� or being unable to cut down on consumption to using ever
larger amounts of cannabis to get the same effect. Applying these same measures
to alcohol, it turns out that marijuana is just as addictive as alcohol for
adults and even more so for teenagers
(see figure). That shocks most marijuana
users, but not Kandel, who believes kids may be unusually 鈥渟ensitive鈥� to
marijuana for biological as well as social reasons. The way she sees it, the
reason we have so many alcoholics is simply that there are so many people
drinking.FIG-21224702.jpg
The problem with this kind of research is that it all depends on what is
meant by addiction. A drug addict is usually seen as a person liable to both
withdrawal symptoms and long-term damage to their health. But Kandel鈥檚
self-report criteria are based on a broader definition. If we applied them to
coffee, vast numbers of us would qualify as addicts. Similarly, many people
might describe themselves as 鈥渁ddicted鈥� to shopping or television or chocolate.
Kandel鈥檚 analysis suggests young marijuana smokers are more likely to show
symptoms of dependence than their beer-swilling contemporaries, but it doesn鈥檛
tell us which substance is the more dangerously addictive.
What is clear is that as users enter their 20s, they report this dependence
far less frequently. And of the people who are still smoking the drug in their
50s, fewer than one in 30 qualify in her analysis as being dependent. Addiction
rates for nicotine follow the opposite trend.
This leads to what is perhaps the most telling statistic about the addictive
powers of cannabis: more than 90 per cent of people who have ever used the drug
have long since quit. While most people continue drinking and cigarette smoking
long after the first flush of youth, people drop the weed in droves after the
age of 30.
CLAIM THREE: 鈥淪moking marijuana can lead to abnormal functioning of lung
tissue . . .鈥�
SMOKING a couple of joints is as bad for your lungs as consuming a whole
packet of cigarettes, say the anti-dope brigade. Their opponents say smoking
marijuana has never caused anyone to die from lung cancer. So, is marijuana
smoke more鈥攐r less鈥攄angerous than tobacco smoke?
The person to ask is Donald Tashkin, a lung expert at the University of
California at Los Angeles. For the past 15 years, Tashkin鈥檚 team has been
keeping a close eye on the respiratory systems of more than 130 regular
marijuana smokers, comparing them with groups of people who smoke either just
tobacco, tobacco and marijuana, or nothing at all. It鈥檚 the biggest study of its
kind in the world. And the results so far suggest that in some respects, yes,
marijuana is more dangerous than cigarettes. But in one important respect,
joints may actually be better for you鈥攅specially if you鈥檙e an athlete.
First, the bad news. While the cigarette smokers in the study were ploughing
through 20 or more a day, the marijuana smokers seldom consumed more than three
or four joints. Despite this, the marijuana smokers coughed and wheezed as much
as the cigarette smokers. In both groups, about one in five people complained of
coughing up phlegm and suffering bouts of bronchitis.
And when it came to cellular damage to the lungs, there was also little to
choose between them. Both groups had too many mucus-secreting cells lining their
airways and too few hair cells, and both groups showed evidence of abnormalities
in cell nuclei and changes in genes known to have an early role in the
development of cancers.
The similarity may seem puzzling given that the marijuana smokers were
consuming so much less plant material. But there are good reasons for it, says
Tashkin. The first is that joints yield up to three times the tar of cigarettes
because they are more loosely packed and don鈥檛 have filters. The second reason
is that marijuana smokers inhale more deeply and hold their breath longer.
鈥淲e actually quantified this and found that the breath-holding time was
increased about fourfold,鈥� says Tashkin. 鈥淭hat resulted in about a 40 per cent
greater deposition of tar.鈥� Tashkin鈥檚 final factor鈥攃ontested by some
researchers鈥攊s that marijuana smoke is richer in benzopyrene and other
polycyclic aromatics known to trigger cancerous changes in cells.
So smoking marijuana can cause lung cancer, after all? Well, maybe. Despite
the gloomy cell biology, epidemiologists have so far failed to find a link
between marijuana and serious lung diseases. That might be because there isn鈥檛
one. Or it might be because 鈥渢he marijuana epidemic鈥� (as Tashkin calls it) is
still young and the people who started smoking in the 1960s haven鈥檛 reached an
age when cancers become common.
Meanwhile, some researchers are worried about another aspect of marijuana
smoke鈥攊ts ability to interfere with immune cells that help to fight off
lung infections. Tashkin鈥檚 team has just discovered that immune cells isolated
from the lungs of marijuana users are unusually bad at killing bacteria, 35 per
cent worse, in fact, than similar cells taken from cigarette smokers. The
marijuana-exposed cells were also below par at producing molecules needed to
mount inflammatory responses. In normal marijuana smokers, the effects may be
too slight to make much difference. Tashkin fears, however, that the same might
not be true in people with AIDS, many of whom use cannabis to stimulate their
appetites.
Footballer鈥檚 fancy
There鈥檚 some good news, though, for dope-smoking cricketers and footballers:
marijuana smoke won鈥檛 lead to blocked airways or emphysema. Despite all the
cellular changes noted by Tashkin鈥檚 team, the researchers found that even heavy
smoking of marijuana had no impact on any physical measure of lung function. In
fact, among their subjects, smoking three joints per day caused no greater rate
of decline in lung capacity and the ability to breathe than smoking no marijuana
per day.
And the reason for this silver lining? It could well be back to those
sluggish immune cells, speculates Tashkin: 鈥淚f cannabis impairs the ability of
immune cells to produce inflammatory cytokines, you might be spared mucosal
damage in peripheral airways.鈥�
CLAIM FOUR: 鈥淢arijuana causes long-term changes in the brain similar to those
seen with other drugs of abuse . . .鈥�
BACK in the 1970s, animal experiments led to groundless fears that marijuana
blew holes in brain tissue. The experiments organisations like NIDA now fund are
more sophisticated but the controversy still rages.
George Koob, an addiction researcher from The Scripps Research Institute in
La Jolla, California, claims the new message from the animals is simple: 鈥淭he
more we discover about the neurobiology of addiction the more common elements
we鈥檙e seeing between THC (tetrahydrocannabinol, the main active ingredient in
cannabis) and other drugs of abuse.鈥� And for Koob, one of these newly discovered
鈥渃ommon elements鈥� is marijauna鈥檚 ability to trigger chemical changes in the
brain that lead to strong withdrawal symptoms.
In humans, some researchers claim to see clear evidence of insomnia, anxiety
and even flu-like symptoms in heavy cannabis users who abstain. But if there鈥檚 a
consensus, it鈥檚 that symptoms are mild and variable. By contrast, Koob鈥檚 rats
are shivering wrecks. Does this mean marijuana is more addictive than we
think?
Not a bit of it, says Roger Pertwee, a university pharmacologist and
president of the Cannabinoid Research Society. That鈥檚 because those symptoms
aren鈥檛 so much observed as manufactured. The animals are injected with high
doses of THC, then injected with a second chemical to block cannabis receptors
in the brain. Without the block, the sharp withdrawal symptoms can鈥檛 be seen
because cannabis clears so slowly that even heavily doped rats are likely to
experience a gentle wind down.
Another debate rages over animal studies into the short-term effects of
marijuana on brain chemistry. Heroin, cocaine, alcohol and nicotine all trigger
a surge in the chemical dopamine in a small midbrain structure called the
nucleus accumbens. Many researchers regard this as a hallmark of an addictive
substance.
Last year, experiments showed that cannabis presses the same dopamine button
in rats, leading to claims that the drug must be more addictive than previously
thought. To critics, it is just another example of those old exaggerated
fears.
What nobody tells you, says John Morgan, a pharmacologist at City University
of New York Medical School, is that rats don鈥檛 like cannabis. It鈥檚 easy for them
to get hooked on heroin or cocaine鈥攂ut not marijuana. Nor, Morgan claims,
are researchers exactly open about awkward observations, such as the fact that
there are plenty of nonaddictive drugs that stimulate dopamine in the brain.
It鈥檚 easy to understand why biologists want to find simple chemical traits
that are shared by all addictive drugs. Unfortunately, the differences are as
important as the similarities when it comes to weighing the relative risks and
pleasures involved in taking drugs. And subjectively at least, the intense rush
of cocaine and orgasm-like high of heroin have little in common with dope鈥檚
subtler effects.
* * *
Drop in with Dr Dave
DAVID SMITH is professor of toxicology at the University of California鈥檚 San
Francisco Medical Center. He has also been running a free clinic in the Haight
Ashbury area of San Francisco since 1967. He has yet another view of what
constitutes addiction.
Addiction used to be defined in terms of the severity of the withdrawal. Then
we started seeing people who used amphetamines compulsively. But their
withdrawal was just a mild crash. They鈥檇 fall asleep or perhaps get a little
depressed.
That鈥檚 when I coined the idea of the three Cs: Compulsion, loss of Control,
and Continued use despite adverse consequences, as a definition of
addiction.
For cannabis, withdrawal was characterised by anxiety and insomnia. It wasn鈥檛
significant physical withdrawal, but that didn鈥檛 mean it wasn鈥檛 addicting. We
would see people use compulsively every day, stop going to school, and spend all
their money on marijuana. The toxicity was lower than for heroin, but it still
fits into our definition of addiction.
The people we see are smoking potent forms of marijuana, spending a
significant amount of their income on it, and suffering psychotic reactions,
anxiety and depression. But if you smoke a joint at the Filmore auditorium on a
Friday night and have a wonderful time, you don鈥檛 go see the Haight Ashbury
clinic. And we don鈥檛 know how many people like that are out there.
I鈥檓 an opponent of legislation, I prefer medicalisation. If marijuana were
legalised tobacco companies would be the main distributors and would target
youth. You鈥檇 have the equivalent of Joe Camel for marijuana.