Cannabis and mental health: key facts
For many of us, cannabis is a way to relax – 2
million people in the UK smoke it and half of all 16 to 29 year
olds have tried it. But research suggests that it can cause
problems in some vulnerable people.
How does cannabis work?
When smoked, cannabis from the lungs
goes into the blood and is carried to every part of the body.
Several chemicals in cannabis bind to receptors in areas of the
brain that deal with pleasure, memory, thought, concentration and
the awareness of time. There are two main kinds of chemical
- A group called the cannabinoids, which seem to give you the
more pleasant effects - feeling relaxed, happy, sleepy, with
colours appearing more vivid and music sounding better.
- THC, which seems to produce hallucinations, anxiety and
These feelings don't usually last long -
although as the drug can stay in your system for some weeks,
subtle effects can last a few days. Long-term use can make you
depressed and make you less motivated.
What is the risk to mental health?
1600 Australian children aged 14 to 15 were
studied for seven years. The ones who used cannabis every day
were 5 times more likely to become depressed and anxious by
the end of the study.
- If you start smoking cannabis before 15, you are 4 times more
likely to develop a psychotic illness.
- The more cannabis you use, the more likely you are to develop
It isn't clear why cannabis use in adolescence
seems to have such an effect, but it may be because the brain is
Is there such a thing as ‘cannabis
Some people seem to get a short period of
psychosis that is brought on by cannabis but which stops soon after
the cannabis is stopped.
If it's so dangerous, why don't more of my friends get
Probably because most people don't use
cannabis before they are 15 and they don't go on smoking
large amounts. Psychotic illness is quite unusual anyway – only
about 1 in 200 people have it at any given time. Most of us
probably don't know that many people so, even if cannabis does
increase the risk, you aren't likely to notice an ”epidemic” among
the people you know.
What about other effects?
- Education: the connection
isn't clear, but regular cannabis use does seem to affect how you
do at school or college.
- Employment: cannabis users are more likely to
leave work without permission, spend work time on personal matters
or daydream. Regular users report that it has interfered with their
work and social life.
- Driving: a recent study in France showed
that cannabis users are more than twice as likely to be the cause
of a fatal crash than to be one of the victims.
Is cannabis addictive?
It has some of the features of addictive
drugs – a regular user has to take more and more to get the same
effect (tolerance) and can get withdrawal symptoms.
3 out of 4 long-term users get cravings,
half become irritable and 7 out of 10 switch to tobacco
to try to stay off cannabis. Many find that they spend much
of their life seeking, buying and using it. It is probably about as
hard to stop as tobacco.
What about skunk and stronger varieties of
The amount of the main active ingredient, THC,
in herbal cannabis varies from 1% up to 15%. The newer strains,
including skunk, can have up to 20%. On the whole, the newer
varieties are probably about 2 or 3 times stronger than
those available 30 years ago. They make you relaxed and cheerful
more quickly, but also produce more unpleasant effects.
How can I cut down my use of cannabis?
Guidance on cutting down and stopping
suggests that you:
- write down your reasons for wanting to change
- plan how you will change
- plan how to cope with withdrawal symptoms
- have a back-up plan.
You can also work through the leaflet on the
What other support can I get?
What about professional help?
Your GP or practice nurse can put you in touch
with a counsellor, support group or NHS substance misuse service.
These can help you to stop taking cannabis, to cut down the amount
you use and to reduce its impact on your life. Some now have
services especially for cannabis users.
For more in-depth information see our main
leaflet: Cannabis and Mental
This leaflet reflects the most up-to-date evidence at the time
Produced by the RCPsych Public Education Editorial Board.
Series Editor: Dr Philip Timms
Reviewed by Dr Ros Ramsay
© January 2014. Due for review: January 2016. Royal College of
Psychiatrists. This leaflet may be downloaded, printed out,
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