THE BIG QUESTION: SO HOW DANGEROUS IS CANNABIS?

Why are we asking this question now?

The head of the UN's anti-drugs office has said that cannabis use has
turned into a major pandemic which is causing as much harm as cocaine
and heroin. Antonio Maria Costa also implicitly criticised countries
such as Britain for relaxing the law on the possession of cannabis.

"Policy reversals leave young people confused as to just how
dangerous cannabis is," Mr Costa said. "With cannabis-related health
damage increasing, it is fundamentally wrong for countries to make
cannabis control dependent on which party is in government. Today,
the harmful characteristics of cannabis are no longer that different
from those of other plant-based drugs such as cocaine and heroin."

What is cannabis?

The most commonly used illicit drug in Britain, if not the world,
also called marijuana, it is produced from certain parts of the
Cannabis sativa plant and comes in various forms - dried leaves,
concentrated resin known as hashish, or distilled oil. The strongest
parts of the plant are the female flowering tops, which are prevented
from going to seed by growing them in a pollen-free environment.
Sensemillia, as this form of cannabis is sometimes called, is strong
because none of the plant's energy goes into making seeds, but
instead produces the psychoactive substances which cause the desired effect.

Cannabis grows wild in many parts of the world, from Poland and
Hungary to Afghanistan, India and China. Its dried leaves or resin
have been smoked by varied cultures over many thousands of years.
Cannabis has been used in societies ranging from the Hindus of India,
the Thracians of southern Europe and the ancient Scythians, who liked
to smoke it in a steam room. Indeed the charred seeds of cannabis
have been found at a Stone Age burial site in Romania, and cannabis
was first documented as a herbal remedy in a Chinese pharmacy text of
the first century AD.

Why do people take it?

Cannabis is a psychoactive substance; in other words, it affects the
brain. But it also affects other parts of the body. It increases
pulse rate, decreases blood pressure, causes bloodshot eyes and
increases appetite. However, it is the effects on the brain that
cause the feelings of calm euphoria and gentle elation that many users enjoy.

The drug has a mild sedative effect but the experience depends
greatly on individual mood and the social environment at the time it
is taken. Some people get the giggles and become talkative, others
become subdued and quiet - the classic symptoms of being "stoned".
Many people feel less inhibited while under the influence of
cannabis, in much the same way as drinking alcohol, which is why it
is a common party drug.

What does it do to the brain?

The most active ingredient of cannabis is a chemical called
tetrahydrocannabinol (THC). It can pass across the biological barrier
that separates the brain from the bloodstream, and in doing so
penetrates the central nervous system. Here, it acts on the natural
proteins or receptors that control nerve impulses passed from one
part of the brain to another.

Cannabinoids such as THC act on a specific protein receptor that is
widely distributed in the brain. As a result it interferes with
concentration and thought, memory, pain perception and muscle
co-ordination. THC particularly interferes with the cerebellum - the
"autopilot" of the brain - which is important for balance, posture,
and co-ordination of movement. The drug also affects the hippocampus,
which is important for the formation of memory.

These influences on the brain help to explain why cannabis
intensifies ordinary sensory experiences, such as eating, watching
films or listening to music. They also explain why users get a false
sense of how time passes, and why they suffer from various problems
with short-term memory, poor reaction time and general unsteadiness.

Are there any more dangerous side-effects?

This is a hotly disputed topic. Cannabis does not produce physical
dependency, as does heroin, but some people who use it regularly can
become psychologically dependent. Cannabis smoke is carcinogenic, and
so can contribute to lung cancer, just like tobacco smoke. And
regular smoking can exacerbate existing respiratory problems, such as
asthma, bronchitis and wheezing.

A few studies have suggested that regular users may also have
impaired immune systems, and there is little doubt that driving while
stoned is dangerous - one study found that smoking cannabis doubles
the risk of fatal car crashes. According to a study in The Lancet,
large doses of THC produce confusion, amnesia, delusions,
hallucinations, anxiety and agitation. "Such reactions are rare,
occurring after unusually heavy cannabis use; in most cases they
remit rapidly after abstinence from cannabis," it says.

The really important issue is whether cannabis can cause serious,
long-term problems for a person's mental health. Earlier this year
the Advisory Council on the Misuse of Drugs concluded that there may
be a link between cannabis use and the onset of psychotic illnesses,
although there was insufficient evidence to state that frequent users
were more likely to develop schizophrenia. Nevertheless, several
studies have suggested that there may well be an association between
smoking cannabis in adolescence and mental illness in later life -
including schizophrenia.

What does the stronger version do to you?

It has been suggested that the smoking of more potent forms of
cannabis, known as "skunk", can result in something called cannabis
psychosis, although this has not been conclusively proved. Skunk is a
generic name used to describe the 100 or so varieties of cannabis
plant that have higher-than-average levels of THC. Skunk may also
contain higher levels of the 40 other substances in cannabis that are
thought to be capable of having an effect on the body.

Traditional varieties of cannabis have a THC content of between 2 and
4 per cent, while some varieties of skunk can have THC levels of up
to 20 per cent. Some users say the immediate effect of smoking skunk
is that they get stoned more quickly. They also report higher levels
of transient hallucinations, which are particularly common in people
who have already taken LSD, a known hallucinogenic drug.

Skunk's potency can sometimes catch people out if they have been used
to more dilute forms of cannabis. As a result they can suffer from
anxiety attacks and feelings of mild paranoia. However, there is no
evidence to suggest that smoking skunk poses any new risks compared
with the heavy smoking of weaker forms of cannabis.

Is cannabis medicinal?

Cannabis has a long history as a folk remedy, and some of its natural
constituents are reported to have therapeutic value for illnesses
such as asthma, glaucoma, mild to severe muscle spasms and pain, as
well as anorexia and mood disorders.

Is smoking cannabis really that bad for you?

Yes...

* There is convincing evidence to suggest a link between heavy use
and serious mental illness

* Cannabis smoke is just as dangerous as cigarette smoke in causing
lung disease

* Driving while even mildly stoned significantly increases the risk
of fatal accidents

No...

* There is no evidence that cannabis causes physical dependency in
the manner of heroin or cocaine

* Mild users of cannabis are not more likely to become addicted to
'harder drugs'

* Many long-term users of cannabis lead normal, healthy lives which
they find enhanced by recreational use of the drug

Why are we asking this question now?

The head of the UN's anti-drugs office has said that cannabis use has
turned into a major pandemic which is causing as much harm as cocaine
and heroin. Antonio Maria Costa also implicitly criticised countries
such as Britain for relaxing the law on the possession of cannabis.

"Policy reversals leave young people confused as to just how
dangerous cannabis is," Mr Costa said. "With cannabis-related health
damage increasing, it is fundamentally wrong for countries to make
cannabis control dependent on which party is in government. Today,
the harmful characteristics of cannabis are no longer that different
from those of other plant-based drugs such as cocaine and heroin."

What is cannabis?

The most commonly used illicit drug in Britain, if not the world,
also called marijuana, it is produced from certain parts of the
Cannabis sativa plant and comes in various forms - dried leaves,
concentrated resin known as hashish, or distilled oil. The strongest
parts of the plant are the female flowering tops, which are prevented
from going to seed by growing them in a pollen-free environment.
Sensemillia, as this form of cannabis is sometimes called, is strong
because none of the plant's energy goes into making seeds, but
instead produces the psychoactive substances which cause the desired effect.

Cannabis grows wild in many parts of the world, from Poland and
Hungary to Afghanistan, India and China. Its dried leaves or resin
have been smoked by varied cultures over many thousands of years.
Cannabis has been used in societies ranging from the Hindus of India,
the Thracians of southern Europe and the ancient Scythians, who liked
to smoke it in a steam room. Indeed the charred seeds of cannabis
have been found at a Stone Age burial site in Romania, and cannabis
was first documented as a herbal remedy in a Chinese pharmacy text of
the first century AD.

Why do people take it?

Cannabis is a psychoactive substance; in other words, it affects the
brain. But it also affects other parts of the body. It increases
pulse rate, decreases blood pressure, causes bloodshot eyes and
increases appetite. However, it is the effects on the brain that
cause the feelings of calm euphoria and gentle elation that many users enjoy.

The drug has a mild sedative effect but the experience depends
greatly on individual mood and the social environment at the time it
is taken. Some people get the giggles and become talkative, others
become subdued and quiet - the classic symptoms of being "stoned".
Many people feel less inhibited while under the influence of
cannabis, in much the same way as drinking alcohol, which is why it
is a common party drug.

What does it do to the brain?

The most active ingredient of cannabis is a chemical called
tetrahydrocannabinol (THC). It can pass across the biological barrier
that separates the brain from the bloodstream, and in doing so
penetrates the central nervous system. Here, it acts on the natural
proteins or receptors that control nerve impulses passed from one
part of the brain to another.

Cannabinoids such as THC act on a specific protein receptor that is
widely distributed in the brain. As a result it interferes with
concentration and thought, memory, pain perception and muscle
co-ordination. THC particularly interferes with the cerebellum - the
"autopilot" of the brain - which is important for balance, posture,
and co-ordination of movement. The drug also affects the hippocampus,
which is important for the formation of memory.

These influences on the brain help to explain why cannabis
intensifies ordinary sensory experiences, such as eating, watching
films or listening to music. They also explain why users get a false
sense of how time passes, and why they suffer from various problems
with short-term memory, poor reaction time and general unsteadiness.

Are there any more dangerous side-effects?

This is a hotly disputed topic. Cannabis does not produce physical
dependency, as does heroin, but some people who use it regularly can
become psychologically dependent. Cannabis smoke is carcinogenic, and
so can contribute to lung cancer, just like tobacco smoke. And
regular smoking can exacerbate existing respiratory problems, such as
asthma, bronchitis and wheezing.

A few studies have suggested that regular users may also have
impaired immune systems, and there is little doubt that driving while
stoned is dangerous - one study found that smoking cannabis doubles
the risk of fatal car crashes. According to a study in The Lancet,
large doses of THC produce confusion, amnesia, delusions,
hallucinations, anxiety and agitation. "Such reactions are rare,
occurring after unusually heavy cannabis use; in most cases they
remit rapidly after abstinence from cannabis," it says.

The really important issue is whether cannabis can cause serious,
long-term problems for a person's mental health. Earlier this year
the Advisory Council on the Misuse of Drugs concluded that there may
be a link between cannabis use and the onset of psychotic illnesses,
although there was insufficient evidence to state that frequent users
were more likely to develop schizophrenia. Nevertheless, several
studies have suggested that there may well be an association between
smoking cannabis in adolescence and mental illness in later life -
including schizophrenia.

What does the stronger version do to you?

It has been suggested that the smoking of more potent forms of
cannabis, known as "skunk", can result in something called cannabis
psychosis, although this has not been conclusively proved. Skunk is a
generic name used to describe the 100 or so varieties of cannabis
plant that have higher-than-average levels of THC. Skunk may also
contain higher levels of the 40 other substances in cannabis that are
thought to be capable of having an effect on the body.

Traditional varieties of cannabis have a THC content of between 2 and
4 per cent, while some varieties of skunk can have THC levels of up
to 20 per cent. Some users say the immediate effect of smoking skunk
is that they get stoned more quickly. They also report higher levels
of transient hallucinations, which are particularly common in people
who have already taken LSD, a known hallucinogenic drug.

Skunk's potency can sometimes catch people out if they have been used
to more dilute forms of cannabis. As a result they can suffer from
anxiety attacks and feelings of mild paranoia. However, there is no
evidence to suggest that smoking skunk poses any new risks compared
with the heavy smoking of weaker forms of cannabis.

Is cannabis medicinal?

Cannabis has a long history as a folk remedy, and some of its natural
constituents are reported to have therapeutic value for illnesses
such as asthma, glaucoma, mild to severe muscle spasms and pain, as
well as anorexia and mood disorders.

Is smoking cannabis really that bad for you?

Yes...

* There is convincing evidence to suggest a link between heavy use
and serious mental illness

* Cannabis smoke is just as dangerous as cigarette smoke in causing
lung disease

* Driving while even mildly stoned significantly increases the risk
of fatal accidents

No...

* There is no evidence that cannabis causes physical dependency in
the manner of heroin or cocaine

* Mild users of cannabis are not more likely to become addicted to
'harder drugs'

* Many long-term users of cannabis lead normal, healthy lives which
they find enhanced by recreational use of the drug