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Wednesday, 03 August 2016 11:24

The Five Most Addictive Substances On Earth – And What They Do To Your Brain Featured

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What are the most addictive
drugs? This question seems
simple, but the answer depends on
whom you ask. From the points of
view of different researchers, the
potential for a drug to be addictive
can be judged in terms of the harm
it causes, the street value of the
drug, the extent to which the drug
activates the brain’s dopamine system,
how pleasurable people report
the drug to be, the degree to
which the drug causes withdrawal
symptoms, and how easily a person
trying the drug will become
There are other facets to
measuring the addictive potential
of a drug, too, and there are even
researchers who argue that no drug
is always addictive. Given the varied
view of researchers, then, one
way of ranking addictive drugs is
to ask expert panels. In 2007,
David Nutt and his colleagues
asked addiction experts to
do exactly that – with some interesting
1. Heroin
Nutt et al.’s experts ranked
heroin as the most addictive drug,
giving it a score of 3 out of a maximum
score of 3. Heroin is an opiate
that causes the level of
dopamine in the brain’s reward
system to increase by up to 200%
in experimental animals. In addition
to being arguably the most addictive
drug, heroin is dangerous,
too, because the dose that can
cause death is only five times
greater than the dose required for a
Heroin also has been rated
as the second most harmful drug
in terms of damage to both users
and to society. The market for illegal
opiates, including heroin, was
estimated to be $68 billion worldwide
in 2009.
2. Cocaine
Cocaine directly interferes
with the brain’s use of dopamine
to convey messages from one neuron
to another. In essence, cocaine
prevents neurons from turning the
dopamine signal off, resulting in
an abnormal activation of the
brain’s reward pathways. In experiments
on animals, cocaine caused
dopamine levels to rise more than
three times the normal level. It isestimated that between 14-20m
people worldwide use cocaine and
that in 2009 the cocaine market
was worth about $75 billion.
Crack cocaine has been
ranked by experts as being the
third most damaging drug and
powdered cocaine, which causes a
milder high, as the fifth most damaging.
About 21% of people who
try cocaine will become dependent
on it at sometime in their life. Cocaine
is similar to other addictive
stimulants, such as methamphetamine
– which is becoming more of
a problem as it becomes more
widely available – and amphetamine.
3. Nicotine
Nicotine is the main addictive
ingredient of tobacco. When
somebody smokes a cigarette,
nicotine is rapidly absorbed by the
lungs and delivered to the brain.
Nutt et al’s expert panels
rated nicotine (tobacco) as the third
most addictive substance.
More than two-thirds of
Americans who tried smoking reported
becoming dependent during
their life. In 2002 the WHO estimated
there were more than 1 billion
smokers and it has been
estimated that tobacco will kill
more than 8m
people annually
by 2030. Laboratory
animals have
the good sense
not to smoke.
However, rats
will press a button
to receive
nicotine directly
into their bloodstream
– and this
causes dopamine
levels in the brain’s reward system
to rise by about 25-40%.
4. Barbiturates (‘downers’)
Barbiturates – also known
as blue bullets, gorillas, nembies,
barbs and pink ladies – are a class
of drugs that were initially used to
treat anxiety and to induce sleep.
They interfere with chemical signalling
in the brain, the effect of
which is to shut down various
brain regions. At low doses, barbiturates
cause euphoria, but at
higher doses they can be lethal because
they suppress breathing. Barbiturate
dependence was common
when the drugs were easily available
by prescription, but this has
declined dramatically as other
drugs have replaced them. This
highlights the role that the context
plays in addiction: if an addictive
drug is not widely available, it can
do little harm. Nutt et al’s expert
panels rated barbiturates as the
fourth most addictive substance.
5. Alcohol
Although legal in the US
and UK, alcohol was scored by
Nutt et al.’s experts 1.9 out of a
maximum of 3. Alcohol has many
effects on the brain, but in laboratory
experiments on animals it increased
dopamine levels in the
brain’s reward system by 40-360%
– and the more the animals drank
the more dopamine levels increased.
Some 22% of people who
have taken a drink will develop dependence
on alcohol at some point
during their life. The WHO has estimated
that 2 billion people used
alcohol in 2002 and more than 3m
people died in 2012 due to damage
to the body caused by drinking. Alcohol
has been ranked as the most
damaging drug by other experts,
Eric Bowman
Lecturer in Psychology
and Neuroscience,
University of St Andrews

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