Cannabis and mental health

You could be forgiven for thinking cannabis was a major cause of serious mental illness, given the nature of the reporting on the media over the past 10 years or so, The "Reefer madness V2" scare was used to great effect by prohibition campaigners, enthusiastically supported by most sections of the media and used by the government as a reason to keep prohibition going.

In truth this is a complex issue and while it is true to say that cannabis isn't the cause of mental illness some have claimed, it is also true that there is an important connection to understand.

Information on this page was originally compiled with the help of the mental health charity RETHINK in 2005 and has since been updated


Brain care and under 18's binge toking
Is cannabis a drug?
What is mental illness?
Are there links between cannabis use and mental health problems?
The compounds in cannabis
Does cannabis make mental illness worse or does it help?
The thoughts of Boojam

UKCIA would like to thank RETHINK for help in writing this page and also Boojam, a cannabis user who has long had problems with manic depression, for his thoughts.

Brain care

You get stoned because of a combination effect of several active chemicals which we call drugs, they're "active" because they do things in the brain.

By design or accident some of the chemicals in cannabis are the same shape as chemicals which occur in the brain that regulate the way the brain (and much of the body) works.

Most drugs used for fun or escapism - perception changing - work in something like this way, so if you don't like the idea of altering the way your brain works, don't do drugs - simple as that...

Out of your head - Lifeline info

The now defunct Manchester based Lifeline's "Out of your head" leaflet gave a good description of mental health problems and the way cannabis might complicate them. It Contained some good information about how cannabis works and what the symptoms of mental illness can be, but it's no longer avaiable.

The most important bit of advice was:

Young people under 18 are best advised not to get stoned - at least not very often - because their brains are still growing and developing. This is good advice not only for cannabis but also for any drug. Getting stoned is an adult thing, don't give it to young people under 15.

Is cannabis a drug? I thought it was a herb?

Cannabis is a herb - one that contains many different chemicals, some of which are drugs. This does make it different to most things that people call "drugs" and it's a very important distinction.

When people talk about "drug use", they usually mean one specific chemical such as Ecstasy (MDMA), LSD, cocaine, nicotine, caffeine or alcohol. Cannabis isn't like that, getting stoned isn't the effect of just one active chemical, it's the combined effect of several which all do their thing at once - see opposite.

It's important to understand that cannabis can have very different effects depending on the variety or "strain" of the plant because of the ratio of active chemicals is different for each strain.

Different types of cannabis are different and traditionally hash made from cannabis grown for making hash was different to weed which was grown to be used as herb.

Pobably the two most important of these compounds are THC and CBD.

So with cannabis there are two important things to be aware of: how strong and what variety it is - but because of prohibition, there's no way of knowing either for most users.

Some of the strains - what the media likes to call "skunk" - often contain a lot of THC but very little CBD, whereas the traditional forms of hash we used to get before the war on drugs seem to have had getting on for equal amounts of both chemicals. This is a part of the reason some people say modern cannabis is different to what it used to be.

Learn about cannabis and the different types. If possible buy cannabis from people you know who grow their own and take a pride in what they grow. Stronger doesn't mean better.

What is mental illness?

Mental illness is a wide term meaning illness that affects the way a person experiences the world around them and it's far more common than most of us realise. In fact 1 in 4 of the population experience some kind of mental health problem of one kind or another at some time in their lives, although for most it's a minor thing.

One thing that ill people do have in common is that they often experience an irrational stigma from a lot of people. Mental health is still a subject many people don't like to talk about, it frightens them, which is the fear the press plays on.

Mental health care for seriously ill people is covered by the mental health act and in extreme cases ill people can be taken into hospital for compulsory treatment, this is called "sectioning".

It's all very different to physical illnesses, in that people can't be treated for any physical illnesses (even contagious ones) if they don't want to be.

Support is mostly offered through community care but the mental health services in the UK are grossly under funded and this is one reason why, shockingly, a significant number of mentally ill people are caught up in the prison system.

Are there links between cannabis and mental health problems?

Claims of links between cannabis and mental health aren't new but it wasn't until 2004 - a year after cannabis was reclassified to class C - that the issue started to hit the headlines. Mental health campaigners claimed that the risks are not known and were not considered adequately when reclassification happened.

Unfortunately the issue was been taken up by prohibition campaigns and the tabloid press as a campaign to increase punishments for cannabis use, rather than to help understanding.

The campaign for information and further research about cannabis and mental health was led by the mental health charity RETHINK, some of whose members have direct experience of mental illness and the effect cannabis has on ill people either as ill people themselves or carers of people with mental illness.

A lot of people with mental health problems don't just use drugs but they use them heavily - what we can really call abusing drugs. One of the most common drugs they use is cannabis; in some cases it seems to help but in others this use makes the illness worse.

In addition to this complicated situation, some of the effects of cannabis seem similar to the symptoms of psychotic illnesses, but in fact aren't connected with mental illness at all. To make it even more complicated, they are the very effects some people enjoy the most about getting stoned.

A large study was undertaken by Keele University to see if the huge increase in cannabis use had caused a rise in mental ilness. The expected rise was not found, which seems to show that cannabis does not cause mental illness. Read more about it here

In the event the government ignored the evidence and used the mental health issue as an excuse to move cannabis back to class B. The education campaign RETHINK were after never happened.


Perhaps the worst of the brain problems, it's often called a "split personality" but that's wrong. Schizophrenia is what is meant by the common term "madness".

It's better to think of schizophrenia as meaning "split from reality"; ill people hear voices which aren't there, suffer hallucinations and, put simply, don't always experience the real world around them correctly. Schizophrenia usually affects young adults in their late teens and early 20's, there is also a form which affects old people known as "late onset schizophrenia", which is usually less serious. It is important to know that this has always happened, schizophrenia affected the same type of people before cannabis became popular.

People can suffer degrees of the illness and no two people's illness are the same

Many people recover from schizophrenia, but others do not. Some don't get the help they need and have a low quality of life, are socially excluded or find their symptoms unmanageable.

The symptoms of schizophrenia are called a "psychosis", which means ill people experience paranoia attacks, sometimes feeling they are being watched and people are talking about them.

Does cannabis make you mad? UKCIA blog

For more in-deapth information see Cannabis and mental health

For more information on what Schizophrenia is, see the RETHINK site:

Does cannabis cause schizophrenia?

Cannabis isn't a cause of psychotic conditions like schizophrenia in the sense that it directly leads to psychosis. That's obvious - we all know people who've smoked for years and haven't got schizophrenia; we also know people who have psychotic symptoms who haven't used any drugs. Research has also failed to show any increase in rates of psychosis which would have been expected if cannabis did cause the illness, given the use of cannabis has increased so much over the past half century.

There are no specific causes of schizophrenia as no single cause has ever been identified. Theories of a genetic link (the COMT gene) haven't been supported by more recent work, in all honestly its still not known what makes schizophrenia happen. It's better to think of "risk factors" - factors which increase the risk of it developing. Some people put birth complications as the main causal factor in about 40% of cases of schizophrenia, stress is another risk factor and there are many others.

The thing is that if more than one risk factor is present, the chances of developing a psychotic condition goes up, or as researchers put it, the risk factors interact.

Cannabis use might be one of these risk factors, especially for children or young teenagers and especially if they use a lot of it.

One large study carried out in Denmark in 2008 seems to show that people who react badly to cannabis with psychotic symptoms may be likely to develop the illness anyway. The authors write:

"The results agree with those of other studies that show that cannabis predominantly causes psychotic symptoms in those persons who are predisposed to develop psychosis or show signs of psychosis in the absence of cannabis use".

they also say

"Psychotic symptoms after cannabis use should be taken extremely seriously. It is recommended that individuals with a cannabis-induced psychosis ... be treated as though the condition is a first sign of schizophrenia, regardless of predisposition to a psychiatric disorder".

In other words, a bad reaction to cannabis might be an early warning that a person is likely to develop schizophrenia. In any case, it should never be ignored and if you do have what you consider to be a bad reaction to cannabis, don't use cannabis again.

Reefer Madness - a still from the film

"Reefer Madness" - a film from the 1930's


Cannabis compounds

The "active chemicals" in cannabis are complex hydrocarbons, which means they're made mostly of carbon and hydrogen with some extra oxygen molecules. The shape of the chemicals is what's important. In the drawings below there's a carbon atom at the point where the lines meet, each one having four "bonds". The spare bonds (not shown) have hydrogen atoms fastened to them.

Tetrahydrocannabinol THC

THC molecule
Cannabis is famous for containing a chemical called Tetrahydrocannabinol - THC. This is the one which gives the near psychedelic side to getting stoned. It's the chemical you'll hear most about, but it's only one of many cannabis contains. The cannabis effect is not the same as pure THC gives.

Cannabidiol CBD

CBD moleculre

Cannabis is less well known for containing another substance called CBD or cannabidiol. It's almost, but not quite, the same shape as THC and because of this it doesn't fit into the same receptor in the brain that THC fits like a key in a lock.

CBD seems to have good anti-psychotic properties and, although it doesn't make you stoned, it does affect the way THC works.

There are a lot of other similar chemicals in cannabis (see wikipedia for some more info) and this is why cannabis is a complicated substance which needs to be understood and its why different strains of the plant have different effects - it's not just "dope".

Does cannabis make mental illness worse or does it help?

For those who have schizophrenia cannabis is extremely
likely to make the condition worse and to delay recovery

But like many of the issues about cannabis and mental health, it's complicated and some people with certain conditions insist cannabis helps them cope.

People who have schizophrenia are more likely to use (and often overuse) cannabis and other drugs than the population in general, in spite of advice not to do so. This might be because use of drugs gives temporary relief or escape from the voices and other symptoms of the illness. So is the heavy use of drugs a symptom of the illness, or a cause of it?

There is also recent research that suggests that CBD (see above) has antipsychotic benefits, although THC (the main active ingredient) is generally accepted is harmful to people with schizophrenia. The type or strain of cannabis might be very important for ill people, some types may help, others may make things worse possibly depending on the ratio of THC and CBD it contains.

If you suffer from schizophrenia, cannabis is extremely likely to make your illness worse or delay your recovery. Cannabis is not for everybody - be supportive of people with schizophrenia for whom it can do harm.

Bipolar depression

People with bipolar (manic) depression can swing from moods of deep depression to periods of overactive, excited behaviour, this is called "mania".

Between these severe highs and lows there may be relatively stable times, although this isn't always the case. Some people also see or hear things that others around them don't (known as having visual or auditory hallucinations or delusions).

One form of treatment for this illness is to use antipsychotic drugs, so it's no surprise that cannabis can have quite an effect on depression.

But, despite the scare stories in the papers, far from making things worse there are many sufferers of depression who claim cannabis helps their condition.

The fact is, there are different types of depression and cannabis may help with some, but not others and of course, there are different types of cannabis...


The vast majority of people with mental health problems are also heavy tobacco smokers. Because tobacco seems to relieve some of the symptoms in ill people, it isn't generally seen as a problem.

However, illnesses such as schizophrenia are thought to be linked with the regulation of a brain chemical called dopamine and tobacco is known to disrupt that balance.

If you smoke a lot of cannabis with tobacco, you're also going to be smoking a lot of tobacco. Tobacco is also addictive and you could end up smoking cannabis simply to have a joint to satisfy a tobacco craving.

UKCIA strongly advises you not to smoke cannabis with tobacco - See Tokepure.

The thoughts of Boojam

This originally came from a post on the UK420 forum, used here with permission. Boojam suffers from long term depression

Under 18's and binge toking: It's not so much the altering of perception that's potentially harmful to developing teenagers, it's the constant, unrelenting alteration of perception. We're still learning to be "us" at that age, we're not yet who we are destined to become, and it's probably not a very good idea to derail that process by getting hammered every single day.

You can't learn to be "you" if you never get the opportunity to be "you", you can't forge your adult links with consensual reality if you're never in touch with consensual reality. You can't get a handle on your own personal perception of the world if that perception of the world is always altered.

Cannabis isn't a problem in itself, but heavy and habitual use of any substance that alters your perception of reality during the late developmental stage of the minds growth cannot be anything but a bad idea. You've got to anchor the good ship 'Mind' before you go diving to explore the depths.


Most cannabis users have the occasional"session" - when a lot gets smoked and everyone gets very stoned. But if you know someone - especially someone young - who's doing this a lot, perhaps to the exclusion of most other things it might be an idea to check out what's going on. Cannabis isn't for children.


I think until more is known about mental illness itself it's difficult to isolate the role that any single factor plays. I do know that there is a lot said about cannabis and mental illness by people that neither smoke cannabis nor suffer from mental illness, and I do wonder to myself precisely what gives these people the idea that they are qualified to comment on something that they themselves have never experienced. Then of course there is the use of this umbrella term 'mental illness' to describe a number of conditions ranging from the relatively minor to the life destroying, I don't think that does the cause of debate any favours. To kinda highlight those points I am a cannabis smoker and I suffer from mental illness, type 1 bipolar disorder, so I feel qualified to offer an opinion about cannabis and manic depression and depressive illness, but I cannot offer any informed opinion about cannabis and schizophrenia, because I do not suffer from schizophrenia.

I can offer an opinion, but not an informed one - that's kinda my point, there's lots of opinion floating around (much of it wearing the thin guise of scientific research when it is nothing of the sort). My informed opinion regarding cannabis and manic depression/depressive illness is that it generally improves my mood if I am in a depressive phase, but smoking strains with high THC and low CBD when I am towards the manic side of my cycle can make me edgy and anxious. I do not believe that smoking cannabis in any way led to my illness (I was diagnosed, wrongly, with simple depression years before I started smoking, if anything I started smoking to try and find answers for my condition, which I did in the sense that cannabis puts me in a more contemplative frame of mind), and I am convinced that without cannabis I would be less able to live a 'normal' life than I am now, since it also enables me to deal with my alcoholism.

My uninformed opinion of cannabis and schizophrenia is different, however. I do not believe it is a good idea for schizophrenics to smoke cannabis. I do not think there is a causal link, but I suspect that if you have schizophrenia cannabis could conceivably exacerbate the symptoms, and if you are in the early stages of undiagnosed schizophrenia I suspect smoking cannabis may increase your awareness of the symptoms thus speeding the onset. Which again goes back to this umbrella term 'mental illness', looking at cannabis and mental illness is a nonsense, because mental illness is just a convenient term to link otherwise unrelated conditions of the mind. With some forms of mental illness I believe cannabis - the right strains, selected for THC to CBD ratio, can be beneficial. With other forms of mental illness I believe cannabis can be detrimental. I do not believe, however, that cannabis is causal, with any form of mental illness.



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