48 Education and Health Vol.26 No.3, 2008

The purpose of this article is to set out ten
key facts that teachers need to know
about cannabis if they are to be able to inform
the pupils in their care authoritatively and
which ideally they need to actively
communicate when the context or situation
arises:

1. Persistence in cells
Cannabis stays in the body: Some children
will know that cannabis persists in the
system and is detectable for some weeks, but
few will know why. It is because THC
(tetrahydrocannabinol), the psychoactive
ingredient in cannabis is, uniquely among
commonly abused illegal drugs, fat-soluble.
This means it stays in brain cell membranes
for a long time. Fifty per cent is still there a
week later and ten per cent after a month. A
monthly joint will ensure the drug a
permanent presence in the brain.

2. Strength
Cannabis has become ’stronger’ and has
changed: Again some children will know that
cannabis has become ’stronger’ in recent
years but fewer will know by how much, or
that the second difference with the past is the
balance of the content of the cannabis
between the THC content and the CBD
(cannabidiol) content.
THC content in the herbal form of
cannabis in the 1960s was around 1-2%. In
cannabis resin it was 4-6%. The new form of
cannabis, Skunk, which now constitutes
about 80% of the British cannabis market and
is mostly home grown, has a THC content
that now averages 14 to 16%. The “old”
herbal cannabis had approximately equal
amounts of THC and CBD, or cannabidiol,
which is thought to have anti-psychotic
properties which ameliorated the effects of
the THC. With today’s Skunk, which has
virtually no CBD content but more THC, the
THC effects are no longer moderated and
ameliorated. This has implications for
psychosis risk.

3. Brain function and mood
Cannabis does affect brain function and
mood: Nerve cells (neurons) communicate by
releasing chemicals (neurotransmitters).
Their molecules fit into receptor sites by
shape on the next neuron, as a key fits a lock.
One neurotransmitter affected by THC is
dopamine. Most drugs that can be abused,
including cannabis, increase its production.
This is the “pleasure” chemical that gives the
“high” and gives drugs their appeal.

4. Physical dependence
Cannabis use leads to physical
dependence or addiction: THC mimics the
shape of one of the neurotransmitters,
anandamide, replacing it in the brain.
Production of anandamide decreases as it is
being substituted. If a person stops taking
cannabis, the receptor sites will stay empty
and withdrawal will set in: anxiety,
sleeplessness, irritability, even violence can
follow. This is physical dependence.
Withdrawal from cannabis is not as dramatic
as that from heroin as the THC takes much
longer to dissipate in the body.

5. Tolerance, psychological dependence
Cannabis use leads to psychological
dependence: It is the increase in dopamine
which creates the overpowering craving for
drugs that addicts feel - this is psychological
Mary Brett is the UK spokesman for EURAD (Europe against Drugs), a member of Prisons and Addictions Forum - Centre for Policy Studies
and was a biology teacher. To read the report, .Cannabis - a general view of its harmful effects’, visit www.talkingaboutcannabis.com
Mary Brett
Ten key facts that teachers need to know
about cannabis
263.qxd 09/07/2008 15:12 Page 48
Vol.26 No.3, 2008 Education and Health 49
dependence. Dopamine’s increased
production triggers the formation of two
other substances. One damps down the
effects and so more is needed creating
tolerance; the other causes new connections
to be made so the brain becomes more
sensitive to the drug and is reminded of how
pleasurable the experience was. This last
substance persists for a long period of time.
Scientists, through studying the
responsiveness of rats to cocaine, have
identified a mechanism in the brain that
helps to explain why craving for cocaine, and
the risk of relapse, seems to increase in the
weeks and months after drug use is stopped.
Exposure to environmental cues (e.g., people,
places, things) previously associated with
drug use can trigger drug craving, often
leading to relapse1.

6. Mental illness link
A link between cannabis use and mental
illness has been established and papers have
now been published on this link. A faulty
gene which leads to the enhanced production
of dopamine has been found in 25% of
humans2.
If an adolescent with one copy of this gene
uses cannabis his/her risk of developing a
psychotic illness increases by 5 or 6 times.
With two copies of the gene the chances of
such illness increase tenfold.
Schizophrenia patients have an excess of
dopamine. In brain scans, similar damage has
been observed in adolescent daily cannabis
users to that found in non-using adolescent
schizophrenics.
Violence, possibly connected with
psychotic episodes or during withdrawal,
and cases of suicide have been linked with
cannabis. Depression, anxiety, panic attacks
and paranoia can occur3. People who smoke
skunk, the extra strong cannabis grown in
hothouse conditions, are 18 times more likely
to develop psychosis that those who take the
milder forms such as hash (cannabis resin)4.

7. Personality, academic failure
Cannabis use affects academic
performance detrimentally and this is why:
THC interferes with the normal release of all
the neurotransmitters. Concentration,
learning and memory all suffer as new
neuron connections are compromised.
Academic performance and grades fall,
exams are failed and often the student will
drop out of education. Young people become
irritable, even violent, fixed in their ideas and
opinions, cannot plan or solve problems,
struggle to find words, and at the same time
feel lonely, misunderstood and miserable.
Few children using cannabis, even
occasionally, will achieve their full potential5.

8. Medical consequences
Cannabis use has physical as well as
mental health consequences: THC affects
new cells made in the adult body. Men who
smoke marijuana frequently have
significantly less seminal fluid, a lower total
sperm count and their sperm behave
abnormally, all of which may affect fertility
adversely6. Similarly it can lead to
underweight babies and to children who
show hyperactivity, learning and behaviour
problems. Another outcome is a lower
production of white blood cells needed to
protect against disease. Heart attacks have
been attributed to cannabis use. Cannabis
deposits 3 to 4 times as much tar as tobacco
does in the airways. Lung cancer has been
seen to result and also rare head and neck
cancers normally only found in tobacco
smokers over 60. Bronchitis and emphysema
can also occur7.

9. Driving
The Transport Research Laboratory
(TRL) reported in 2000 that, .In terms of road
safety, it cannot be concluded that driving
under the influence of cannabis is not a
hazard, as the effects on various aspects of
driver performance are unpredictable.8. On
the incidence of drugs and alcohol in road
accident fatalities, the TRL found that
cannabis was the most common illegal drug
found in the bloodstream of road accident
victims9.
A 20mg (average) joint is thought to be
equivalent to a person being just over the
263.qxd 09/07/2008 15:12 Page 49
50 Education and Health Vol.26 No.3, 2008
legal drink-drive limit. An alcohol-cannabis
combination is 16 times more dangerous than
using one alone.

10. A ‘gateway’ effect
Cannabis use as a gateway to other drug
use has been much disputed but beyond
argument is the fact that earlier use leads to
heavier and regular use later on: In Australia,
among young adults who had not been using
amphetamines at age 20 years, the strongest
predictor of use at age 24 years was the use of
other drugs, particularly cannabis, at 20
years10. Research in Sweden shows that
cannabis actually “primes” the brains of
animals for other drugs11. A New Zealand
study concluded that, “the use of cannabis in
late adolescence and early adulthood
emerged as the strongest risk factor for later
involvement in other illicit drugs”12.
Teachers have a duty to be able to
authoritatively communicate the risks and
dangers involved with cannabis use.
Currently our school children are being badly
let down.

References

1. Conrad KL, Tseng KY, Uejima JL, Reimers JM, Heng LJ,
Shaham Y, Marinelli M, Wolf ME,. Formation of accumbens
GluR2-lacking AMPA receptors mediates incubation of
cocaine craving. Nature, May 25th 2008
http://www.nida.nih.gov/newsroom/08/NR5-25.html
(Last accessed 4th July 2008)

2. Caspi A, Moffitt T, Cannon M, McLay J, Murray R,
Harrington H, Taylor A, Arsenault L, Williams B, Braithwaite
A, Poulton R, Craig I,. Moderation of the Effect of
Adolescent-Onset Cannabis Use on Adult Psychosis by a
Functional Polymorphism in the COMT Gene. Longitudinal
Evidence of a Gene X Environment Interaction. Biol.
Psychiatry 2005: 57: 1117-1127

3. Murray RM, Morrison PD, Henquet C, Di Forti M,.
Cannabis, the mind and society: the hash realities. Nature
Reviews Neuroscience 8, 885-895 November 2007.
http://www.nature.com/nrn/journal/v8/n11/abs/nrn2253.html
(Last accessed 4th July 2008)

4. Press Release from the Royal College of Psychiatrists,
“People who smoke skunk are 18 times more likely to
develop psychosis”. 2 July 2008.
http://www.rcpsych.ac.uk/pressparliament/
pressreleases2008/bank2008/amcannabis.aspx
(Last accessed 9th July 2008)

5. Van Ours JC, Williams J, 2007b Why parents worry:
Initiation into Cannabis Use by Youth and their Educational
Achievement CEPR Discussion Paper No. 6449.
http://papers.ssrn.com/sol3/papers.cfm?abstract_id=1012269
(Last accessed 4th July 2008)

6. Press Release from University of Buffalo, “Sperm from
Marijuana Smokers Move Too Fast Too Early, Impairing
Fertility, UB Research Shows”. October 13, 2003
http://www.buffalo.edu/news/fast-execute.cgi/articlepage.
html?article=64270009
(Last accessed 9th July 2008)

7. Aldington S et al, Cannabis use and risk of lung cancer: a
case-control study European Respiratory Journal 2008; 31:
280-6.
http://ersj.org.uk/cgi/content/abstract/31/2/280
(Last accessed 4th July 2008)

8. Sexton, BF, Tunbridge, RJ, Brook-Carter, N, Jackson, PG,
Wright, K, Stark, MM, Englehart, K,. The influence of
cannabis on driving. Transport Research Laboratory 2000
http://www.trl.co.uk/store/
report_detail.asp?srid=2633&pid=211
(Last accessed 9th July 2008)

9. Tunbridge RJ, Keigan M, James FJ,. The incidence of
drugs and alcohol in road accident fatalities. Transport
Research Laboratory 2001
www.trl.co.uk/store/downloadreport.asp?id=2650
(Last accessed 9th July 2008)

10. Degenhardt L, Coffey C, Carlin JB, Moran P, Patton
GC,. Who are the new amphetamine users? A 10-year
prospective study of young Australians. Addiction, 102 (8)
1269-1279. 2007.
http://www3.interscience.wiley.com/journal/117968141/
abstract?CRETRY=1&SRETRY=0
(Last accessed 9th July 2008)

11. Ellgren,M,. Neurobiological effects of early life cannabis
exposure in relation to the gateway hypothesis. Thesis. The
Karolinska Institute. 2007.
http://diss.kib.ki.se/2007/978-91-7357-064-0/
(Last accessed 9th July 2008)

12. Fergusson DM, Boden JM, Horwood LJ,. The
developmental antecedent of illicit drug use: Evidence from
a 25-year longitudinal study. Drug and Alcohol Dependence
2008; 96: 165-177.
http://www.ncbi.nlm.nih.gov/pubmed/18423900
(Last accessed 4th July 2008)
263.qxd 09/07/2008 15:12 Page 50