Cannabis and mental health

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Introduction
What is cannabis?
Derivations of cannabis
Cannabis as a drug
Smoking cannabis
Eating cannabis
Potency
How many people use cannabis?
What are the psychological effects of cannabis?
Cannabis, psychosis and schizophrenia
Other psychological effects
What are the physical effects of cannabis?
Is cannabis addictive?
Does cannabis interact with other drugs?
Medical use of cannabis
Legal status
Further reading
Useful contacts
Useful websites

Introduction

This factsheet is primarily for people concerned about the psychological effects of cannabis on themselves and their relatives, and its possible role in the development of psychosis. It may also be of interest to students and professionals.

What is cannabis?

Cannabis is a plant that has been used by humans for thousands of years. For many years, cannabis, also known as hemp, was cultivated for its fibre. Hemp was produced and used for rope, cloth and paper. The names of Hampshire and Hampstead derive from the cultivation of hemp in these areas. Currently there is a limited revival of these uses.

The two most prevalent species of hemp are Cannabis sativa and Cannabis indica. Cannabis sativa was cultivated principally to make hemp, while Cannabis indica was grown mainly for the psychoactive properties of its resins. Plant breeders have crossed these two types to develop the flavours of different hybrids, and to increase the content of the psychoactive components, making a more potent drug. [1]

Cannabis contains chemicals called cannabinoids which are unique to the cannabis plant. These include cannabinol, cannabidiol, and several different forms of tetrahydrocannabinol, one of which, delta-9-tetrahydrocannabinol (THC), is believed to be responsible for most of the psychoactive effects.

THC (as well as nicotine and cocaine) was recently identified in an Egyptian mummy from approximately 950 BC.

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Derivations of cannabis 

Marijuana
Marijuana is a tobacco-like substance produced by drying the leaves and flowering tops of the cannabis plant.

Hashish
Hashish, or cannabis resin, is derived from the unpollinated female plant and also known as sinsemilla (meaning ‘without seed’), and has a higher THC content than herbal marijuana. As the female flowers mature without fertilisation, they continually secrete resin which coats the flowers and small leaves surrounding them. The flowers grow in thick clusters, heavy with resin. Hashish is produced when the resin is separated from the plant material.

Skunk
The name skunk has come to mean any strong cannabis, but originally referred to a plant developed by selective breeding in the 1970s, which is the origin of all the skunk varieties grown today. Nederwiet is the Dutch name for a strong form of skunk grown in the Netherlands. Skunk plants are usually grown under artificial conditions, either under grow lights or using hydroponic (without soil) techniques. The plants can be intensively cultivated to produce a THC content of about 15 per cent, but may be as high as 20 per cent or more. [2] This is very much higher than the content of ‘traditional’ herbal cannabis which is in the region of 3 per cent or less. As a result, the psychoactive effects of using skunk come on rapidly and people may be more likely to experience hallucinations and other effects that may be classed as psychotic.

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Cannabis as a drug

Cannabis is usually smoked, but can also be eaten. The effects experienced depend largely on the concentration of THC in the product used, but also on the relative concentrations of the other psychoactive ingredients.

Smoking cannabis

When cannabis is smoked (in a cigarette known as a joint), the blood in the lungs absorbs the THC. It then goes straight to the heart and from there to the brain. Thus the psychoactive effect – the high – occurs within minutes. [3]

THC also accumulates in other organs such as the liver, kidneys, spleen and testes. It readily crosses from the blood of a pregnant woman into the placenta and reaches the developing foetus. THC is absorbed into fat and remains in the body for a long time.

A week after smoking, about 30 per cent of the THC (and its break-down products) may remain in the body and continue to have subtle mental and physical effects. Regular users may therefore never be free from the effects.

Eating cannabis

If cannabis is eaten rather than smoked, less THC reaches the brain and it takes longer to get there. The peak levels of the drug last longer, but are lower than after smoking. Because of the way cannabis is broken down and absorbed in the body, blood and urine levels do not give a very good measure of the likely effects on behaviour. [4]

Potency

In the past 20 years, farming methods have greatly increased the potency of some cannabis products. In 1995, the mean THC content of hashish seized by law enforcement officers in the UK was 5.8 per cent, and by 2005 this had increased to 14.2 per cent. The potency of hashish did not change significantly over the same period, and that of marijuana increased from 3.9 per cent in 1995 to 8.5 per cent in 2000, after which no figures are available. [5]

The European drugs agency (EMCDDA) Statistical Bulletin for 2006 reports that the maximum potency (as percentage THC) of hashish sold in England and Wales in 2004 was 12 per cent, while that of skunk/nederwiet was 34 per cent. The minimum potency of both types was 1 per cent, and the mean potencies were 3.4 per cent for hashish and 12.7 per cent for skunk. [6]

This means that, while the strength of some varieties of cannabis has not changed significantly, skunk users now may be exposed to very much higher doses of THC than those who smoked cannabis in the 1960s and 1970s, before the original skunk variety was developed. The effects are dose-related, and so are much more marked in those people who use the strongest skunk.

In October 2007, Dean Ames, the head of the Forensic Science Service’s drug unit, was widely reported as saying that skunk accounted for 75 per cent of cannabis seized by police and customs officers in the first half of the year. [7]

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How many people use cannabis?

As cannabis is an illegal drug it is impossible to find exact figures on its use. Data from the British Crime Survey suggest that in 2002-2003 over 3.3 million people used cannabis, the majority of whom were aged 16 to 24 years. There is evidence of a slow decline in cannabis use since 1998, with no sign of any increase since it was reclassified from class B to class C in January 2004. [8] Indeed, figures from the British Crime Survey show that the proportion of 16 to 24–year-olds who had used cannabis in the past year fell from 25 per cent when the change in the law was introduced to 21 per cent in 2006-2007. At the same time the number of seizures of cannabis rose by 54 per cent. [9]

If public perception is that use is increasing, this may be because people are tending to use stronger varieties, with consequences that have a greater public impact than occurs with milder forms.

Findings from the British Crime Survey show that in 2001/2002, people from a mixed cultural background were most likely to have taken an illicit drug. The figures for cannabis use in different cultural groups are shown in the table below. [10]

In all groups, cannabis use is highest in the 16-24 age group and decreases with age.

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What are the psychological effects of cannabis?

Cannabis produces its effects on the brain through interactions between its psychoactive components (especially THC) and particular receptors found on brain cells. It is thought that these receptors usually interact with naturally occurring brain chemicals, one of which has been identified and called anandamide (ananda means ‘bliss’ in Sanskrit). [11] There is little research on this substance, but it has pain-relieving and tranquillising effects in animals.

Cannabis also causes dose-related changes in brain chemicals such as dopamine and serotonin, which are involved in the control of mood and emotion. Different strains of cannabis have different proportions of THC and other chemical (cannabinoid) components, and this accounts for some of the variation in effects between different people, or different occasions.

The main effect of cannabis on mood is that it produces euphoria – a high. Most people’s reason for taking it is ‘pleasure’. The high may be accompanied by changes in perception: colours may seem brighter, music more vivid, emotions more poignant and meaningful. However, it can also cause severe anxiety and panic, and psychosis. Paranoia and hallucinations may occur with high doses. [12]

It is suggested that the unwanted psychological effects of cannabis can be classified as:

• short-lived effects such as anxiety, panic, depression and psychosis, which usual occur after excessive consumption of the drug
• effects on pre-existing mental illness
• cannabis as a risk factor for mental illness
• dependency and withdrawal. [13] 

Cannabis, psychosis and schizophrenia

Depending on the kind that has been used, and your susceptibility to it, cannabis can cause psychotic experiences such as hallucinations, fantasies, depersonalisation and derealisation (feeling out of touch with yourself or your surroundings), feeling a loss of control, fear of dying, irrational panic and paranoid ideas.

In theory, cannabis may cause a psychotic reaction in the following ways:

• Taking a high dose may cause a psychotic reaction with hallucinations or confusion, which goes away after the drug is stopped.
• It may lead to a long-term psychosis that does not go away when the drug is stopped.
• Long-term use may induce psychosis that gets a bit better if the drug is stopped.
• Cannabis may be a trigger for serious mental illness, such as schizophrenia. [14] 

Among people who already have a diagnosis of psychotic illness, cannabis users are thought to experience more psychotic relapses. Again, experience depends on the strength of the type used as well as frequency of use.

Research in young people suggests that using cannabis as a teenager increases the likelihood of experiencing symptoms of schizophrenia in adulthood, and early cannabis use (by age 15) confers greater risk than using it later on (by age 18). This research suggests that, although the majority of adolescents are not harmed by using cannabis, a small minority are. [15]

Results of a Swedish study suggest that cannabis increases the risk of schizophrenia by 30 per cent. However, this does not appear to be reflected in the figures for schizophrenia in the population in general, which have remained constant over a long period. This study also concludes that cannabis has few harmful effects overall, but that there is a potentially serious risk to the mental health of people who use cannabis, particularly in the presence of other risk factors for schizophrenia. [16]

Researchers who examined further published evidence on cannabis and psychosis in 2004 came to the conclusion that, for any individual, using cannabis doubles the risk of developing schizophrenia in later life, and, for the population as a whole, elimination of cannabis use would reduce the incidence of schizophrenia by about 8 per cent, if you assume that it has a causal effect. Cannabis use alone does not cause psychosis, but it is one of the things that may contribute to its development; therefore, using cannabis increases the risk, and some cases of psychosis could be prevented by discouraging cannabis use among vulnerable young people. [17] A response to this report further suggested that adolescents may be more vulnerable to the adverse effects of cannabis than are adults because their brains are still developing. [18] A further study concluded that cannabis use increases the risk of psychotic symptoms in young people, but has a much stronger effect in those with evidence of a predisposition for psychosis (such as a family history of mental illness). [19]

Support for this suggestion is provided by a study in young people of a particular enzyme called COMT (catechol-O-methyl transferase), which is involved in the regulation of the brain chemical dopamine (psychosis is thought to be associated with high levels of dopamine). COMT is produced by a gene, two variants of which occur in the population, and produce two forms of the enzyme, which break down dopamine to different degrees. As with all genes, people inherit one copy from each parent. The study found that people who inherited two ‘good’ subtypes could use cannabis without it affecting their mental health; those with one of each subtype were at slightly more risk of psychosis with cannabis; while in those who had two ‘bad’ subtypes the risk was increased ten-fold. [20] [21]

A further study, reported in The Lancet in July 2007, which analysed reports from 35 published studies, found ‘a consistent increase in incidence of psychosis outcomes in people who had used cannabis’. Their analysis suggested that there was a 40 per cent increase in risk of psychosis in study participants who had ever used cannabis. Effects were larger with frequent use, with an increased risk of up to 200 per cent in those who used cannabis most heavily. [22]

In a written answer to the House of Commons on 18 July 2005, Rosie Winterton MP said that admissions associated with cannabis use rose to 710 in 2003-2004, from 580 in the previous two years. [23] There is some evidence that, since cannabis was down-graded in the UK from a class B to a class C drug in January 2004, psychiatrists have seen further increasing numbers of people being hospitalised with psychotic episodes associated with cannabis use. [24] This is in spite of the fact that overall numbers of people using cannabis have fallen, and a further indication that of those people who use cannabis, more of them are using strong varieties which are more likely to cause adverse effects on mental health.

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Other psychological effects

There are other, less frightening, effects of cannabis on mental functioning. Heavy users may experience lethargy, loss of communication skills and a general lack of ambition. Their faculties do return, however, if they stop smoking. The idea that cannabis use causes long-term memory loss may arise because most heavy smokers are too ‘stoned’ to absorb much information in the first place: cannabis is not thought to affect memories which are already in place, only the ability to store new ones.

Cannabis impairs mental flexibility and problem-solving abilities. It also decreases attention and concentration, and impairs judgement and complex co-ordination (for example, the ability to drive a car or operate machinery). Unlike many drugs, including alcohol, it does not normally make people aggressive; however, there is some evidence that people may commit acts of violence under the influence of cannabis-induced psychotic delusions. [25]

In a study of adolescents in Australia, those who used more cannabis were more likely to develop depression and anxiety, and this was more marked in girls. Young women who used cannabis daily were five times more likely to have depression and anxiety than non-users, and using cannabis weekly doubled the rates of anxiety and depression. There was no evidence that girls who were already depressed before using cannabis were more likely than others to use it. [26]

Other studies, using self-reported questionnaires with groups of users, have reported panic attacks and anxiety in a significant number of users, and depression, tiredness and low motivation. [27]

Recent research using a rat model of depression suggests that cannabis may act as an antidepressant at low doses, increasing serotonin levels in the brain. Higher doses reverse this effect, causing serotonin levels to fall below those of the control group. The researchers reported that this effect was mirrored in their patients who were regular users of cannabis. [28]

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What are the physical effects of cannabis?

Cannabis smokers experience the same health problems as tobacco smokers; including bronchitis, emphysema (a lung condition causing breathing problems), bronchial asthma, and lung cancer. Immediate effects may include light-headedness and faintness. Other effects include increased heart rate, dry mouth, red eyes, impaired motor co-ordination, hunger, and an increased desire for sugar. It can reduce sperm production, disrupt the menstrual cycle, and affect the growth of an unborn child. Extensive use increases the risk to the lungs and reproductive system, and suppresses the immune system. [29]

It is unlikely that anyone has ever died from an overdose of cannabis, but people with heart disease or high blood pressure may be at risk, because it increases the heart rate and places greater stress on the heart.

Cannabis has effects similar to alcohol and benzodiazepines (minor tranquillisers) on the performance of tasks, including both thinking and motor co-ordination. It impairs concentration and short-term memory, and slows reaction times. It will therefore reduce the ability to perform skilled tasks such as driving. After alcohol, cannabis is the drug most commonly found in drivers following fatal accidents, and a French study has shown that driving under the influence of cannabis increases the risk of road accidents. [30]

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Is cannabis addictive?

Cannabis used to be thought of as non-addictive. Some people believe that its use is unlikely to lead to dependency, and that withdrawal is not generally a problem because it is stored in fatty tissues and disperses slowly over a period of days, thus suppressing its own withdrawal symptoms.

However, there is evidence that some people do develop tolerance to many of the effects of cannabis, meaning that increasing doses have to be taken to achieve the same effect. This is associated with withdrawal symptoms, including restlessness, insomnia, anxiety and muscle tremor. This leads users to continue to use cannabis, and therefore become dependent on it. These effects may be a feature of the more powerful types of skunk or nederwiet that are available now.

The number of people seeking help with cannabis use from drug dependency services has increased in recent years. [31]

Does cannabis interact with other drugs?

Very little scientific research has been carried out on cannabis use in combination with other drugs. Possible dangers could include interactions with heart or blood pressure medications, or with drugs that suppress the immune system. In addition, it has been shown that a combination of marijuana with cocaine can lead to dangerous effects on the heart.

Medical use of cannabis

Cannabis has many pharmacological actions and is effective in treating several medical conditions. These include nausea associated with cancer chemotherapy; loss of appetite and physical wasting associated with AIDS; glaucoma (a serious eye disease); muscle spasms occurring in multiple sclerosis and other disorders that produce involuntary muscle contractions; chronic pain, and migraine headaches. [32]

Nabilone, a synthetic version of THC, has been marketed in America for the control of nausea and vomiting caused by chemotherapy for cancer, and to stimulate the appetite in AIDS patients. Nabilone has also been found to significantly reduce anxiety, with postural hypotension (low blood pressure on getting up from lying or sitting, causing dizziness) as the only significant side effect.

Legal status

British law has, until recently, prohibited the use of cannabis for medical purposes. In the last few years, however, some research on medical uses of cannabis has been allowed in this country, and it is possible that cannabis-based drugs may become available for some conditions. However, it currently has no approved medical use.

Cannabis reclassification
In January 2004 cannabis was reclassified from a class B to a class C drug. This means that possession, production and supply are still illegal; only the penalties have been changed. For more details see the Home Office website ‘Tackling Drugs Saving Lives’ at http://drugs.homeoffice.gov.uk/

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Further reading

Understanding addiction and dependency, Mind 2007
Understanding dual diagnosis, Mind 2007
Understanding psychotic experiences, Mind 2004
Understanding the psychological effects of street drugs, Mind, 2007

Useful contacts

DrugScope
40 Bermondsey Street, London SE1 3UD
email: info@drugscope.org.uk
website: www.drugscope.org.uk 
tel: 020 7490 7500
Information on a wide range of drug related topics.

Talk to Frank (National Drugs Helpline)
tel: 0800 77 66 00 (freephone)
textphone: 0800 917 8765
email: frank@talktofrank.com
website: www.talktofrank.com
Website and telephone helpline offering advice, information and support to anyone concerned about drugs and substance misuse, including drug misusers, their families, friends and carers. You can talk to Frank in 120 languages - just call the same number and a translator will be there if necessary.

National Psychosis Service
National Psychosis Unit, Fitzmary 2, Bethlem Royal Hospital, Monks Orchard Road, Beckenham BR3 3BX
tel: 020 3228 4322
email: nps@slam.nhs.uk 
Accepts referrals for patients with problems with psychosis, including cannabis-induced psychosis.

Release
388 Old Street, London EC1V 9LT
helpline: 0845 4500 215
tel: 020 7729 5255
email: ask@release.org
website: www.release.org.uk
Helpline, legal advice and support for drug users, families, friends and professionals.

Turning Point
Standon House, 21 Mansell Street, London E1 8AA
tel: 020 7481 7600
email: info@turning-point.co.uk
website: www.turning-point.co.uk 
Social care charity providing services for people with complex needs, including those affected by drug and alcohol misuse, mental health problems and those with a learning disability.

Useful websites

www.marijuana-anonymous.org
Support for coming off, with groups in various countries including UK.

www.knowcannabis.org.uk 
Helps you assess your cannabis use and its impact on your life, and tells how to make changes if you want to

[1] www.skunk.co.uk
[2] www.seedsman.com/en/cannabis-seeds/skunk
[3] Ashton, CH, 2001, ‘Pharmacology and effects of cannabis: a brief review’, British Journal of Psychiatry, vol 178, pp 101-106.
[4] Ashton, CH, 2001, ‘Pharmacology and effects of cannabis: a brief review’, British Journal of Psychiatry, vol 178, pp 101-106.
[5] Advisory Council on the Misuse of Drugs, 2006, Further consideration of the classification of cannabis under the Misuse of Drugs Act 1971, Home Office.
[6] European Monitoring Centre for Drugs and Drug Addiction (EMCDDA), 2006, Drug availablity and drug markets, Statistical Bulletin. http://stats06.emcdda.europa.eu 
[7] Howie, M, 2007, ‘Majority of cannabis seized is powerful ‘skunk’’, The Scotsman, 16 October.
[8] Advisory Council on the Misuse of Drugs, 2006, Further consideration of the classification of cannabis under the Misuse of Drugs Act 1971, Home Office.
[9] Travis, A, ‘Fewer young people using cannabis after reclassification’, Guardian Unlimited, 25 October, www.guardian.co.uk/drugs/Story/0,,2198881,00.html 
[10] Aust R. and Smith N, 2003, Ethnicity and drug use: key findings from the 2001/2002 British Crime Survey, Home Office.
[11] Robson, P, 2001, ‘Therapeutic effects of cannabis and cannabinoids’, British Journal of Psychiatry, vol 178, pp 107-115.
[12] Ashton, C.H, 2001, ‘Pharmacology and effects of cannabis: a brief review’, British Journal of Psychiatry, vol 178, pp 101-106.
[13] Johns A. 2001, ‘Psychiatric effects of cannabis’, British Journal of Psychiatry, vol. 178, pp.116-122.
[14] Johns A, 2001, ‘Psychiatric effects of cannabis’, British Journal of Psychiatry, vol. 178, pp.116-122.
[15] Arsenault L, Cannon M, Poulton R, Murray R, Caspi A, and Moffit TE, 2002, ‘Cannabis use in adolescence and risk for adult psychosis: longitudinal prospective study’, British Medical Journal vol. 325, pp. 1212-1213.
[16] Zammit S, Allebeck P, Andreasson S, Lundberg I, Lewis G, 2002, ‘Self reported cannabis use as a risk factor for schizophrenia in Swedish conscripts of 1969: historical cohort study’, British Medical Journal vol. 325, pp. 1199-1201.
[17] Arseneault L, Cannon M, Witton J, and Murray R, 2004, ‘Causal association between cannabis and psychosis: examination of the evidence’, British Journal of Psychiatry, vol 184, pp 110-117.
[18] Dervaux A, Goldberger C, Laqueille X, and Krebs M-O, 2004, ‘Cannabis and psychosis’, letter, British Journal of Psychiatry, vol 185, p 352.
[19] Henquet C, Krabbendam L, Spauwen J, Kaplan C, Lieb R, Wittchen H-U, and van Os J, 2005, ‘Prospective cohort study of cannabis use, predisposition for psychosis, and psychotic symptoms in young people’, British Medical Journal, vol 330, 1 Jan, pp 11-13.
[20] Salvage, F. 2005, ‘Of cannabis and psychosis’, Royal Society of Chemistry, EiC September 2005, www.rsc.org/Education/EiC/issues/2005Sept/infochem.asp
[21] Caspi, A, Moffitt, T.E, Cannon, M, McClay, J, Murray, R, Harrington, H, Taylor, A, Arseneault, L, Williams, B, Braithwaite, A, Poulton, R, and Craig, I.W, 2005, ‘Moderation of the effect of adolescent-onset cannabis use on adult psychosis by a functional polymorphism in the catechol-O-methyltransferase gene: longitudinal evidence of a gene X environment interaction’, Biological Psychiatry, vol 57, pp 1117-1127.
[22] Moore, T.H.M, Zammit, S, Lingford-Hughes, A, Barnes, T.R.E, Jones, P.B, Burke, M. and Lewis, G, 2007, ‘Cannabis use and risk of psychotic or affective mental health outcomes: a systematic review’, The Lancet, vol 370, pp 319-328.
[23] Hansard, 18 Jul 2005 : Column 1467W
[24] Owen, J, 2007, ‘Mental illness soars in UK’s skunk hotspots’, The Independent, 21 October.
[25] for example, a report in the Evening Standard, 27 July, 2007, headed ‘Cannabis-fuelled violence’ listed several cases where cannabis was thought to be implicated in psychotic acts of violence.
[26] Patton G.C, Coffey C, Carlin J.B, Degenhardt L, Lynskey M, and Hall W, 2002, ‘Cannabis use and mental health in young people’, British Medical Journal, vol. 325, pp. 1195-1198.
[27] Johns A. 2001, ‘Psychiatric effects of cannabis’, British Journal of Psychiatry, vol. 178, pp.116-122.
[28] Bambico, F, Katz, N, Debonnel, G. and Gobbi, G, 2007, Journal of Neuroscience, 24 October, reported in Care and Health News: www.careandhealth.com, 23 November 2007.
[29] Marijuana, www.streetdrugs.org
[30] Laumon, B, Gadegbeku, B, Martin, J-L, and Biecheler, M-L, 2005, ‘Cannabis intoxication and fatal road crashes in France: population cased case-control study’, British Medical Journal, doi:10.1136/bmj.38648.617986.1F (published 2 December 2005)
[31] National Treatment Agency for Substance Misuse, 2007. Regional media releases - numbers in treatment, 19/10/07. www.nta.nhs.uk/media/default.aspx
[32] Johnson, B.A, 1998, ‘Comment on "Health aspects of cannabis: revisited (Hollister)’, International Journal of Neuropharmacology, vol 1, pp 81-82.

This factsheet was written and updated by Katherine Darton, November 2007.