Kannabis ja suomalainen psykoositutkimus
Toukokuussa suomalaiset tiedotusvälineet uutisoivat näkyvästi
suomalaisesta tutkimuksesta, joka lehtien mukaan osoitti kannabiksen
aiheuttavan skitsofreniaa.
Mm. Helsingin Sanomat otsikoi lauantaina 31.05.2008: Tutkimus: Kannabiksen käyttö lisää skitsofrenian riskiä nuorilla.
(http://www.hs.fi/kotimaa/artikkeli/Tutkimus+Kannabiksen+käyttö+
lisää+skitsofrenian+riskiä+nuorilla/1135236794468 )
nuorisotutkimus “Association of cannabis use with prodromal symptoms of
psychosis in adolescence”, joka julkaistiin The British Journal of
Psychiatry -tiedejulkaisussa. (Association of cannabis use with
prodromal symptoms of psychosis in adolescence. The British Journal of
Psychiatry (2008) 192, 470–471. doi: 10.1192/bjp.bp.107.045740.
http://ukcia.org/research/AssociationOfCannabisUseWithProdromalSymptoms.php )
Tutkimusta uutisoivat likipitäen kaikki suomalaiset tiedotusvälineet ja
se sai julkisuutta myös briteissä. Julkaistuille uutisille oli yhteistä
se, että kannabiksen käytön kerrottiin "lisäävän riskiä", "aiheuttavan
skitsofreniaa" jne eli toimittajien mielestä tämä paljon väitetty
reefer madness -hypoteesi olisi jälleen kerran osoitettu oikeaksi.
Suomessa aiheesta ei käydä avointa keskustelua mutta Britannian julkisen terveydenhuollon (nhs.uk)
kotisivuilla kommentoidaan kyseistä tutkimusta ja heidän
johtopäätöksensä on, että 'because of its design, the study does not
prove that cannabis causes psychosis.'
Mikä tarkoittaa sitä, että tutkimuksen suoritustavan johdosta siitä ei
voi vetää syy-seuraus päätelmiä. Eihän tutkimuksessakaan vedetä niitä
(At best, the researchers can say that cannabis use is “associated
with” or “linked to” the prodromal symptoms. ) mutta toimittajille on
helpompaa tehdä sellaisia otsikoita, joissa ei ole epävarmuutta.
Toiseksi tutkijoiden käyttämä tutkimusväline eli karsittu
kysymyspatteri ei edes mittaa "psykoosia". (Importantly, a positive
“score” on the PROD-screen questionnaire does not diagnose psychosis).
Tutkimukseen osallistuneista 6298 nuoresta 352 ilmoitti käyttäneensä
kannabista ja sai muita enemmän positiivisia tuloksia tutkijoiden
käyttämässä kysymyspatterissa, joka ei kuitenkaan mittaa "psykoosia"
vaan esimerkiksi kannabiksen päihtymysoireita, mm. kieltolain
aiheuttamaa kyttäfiilistä. Eikö olisi aiheellista kertoa nuorten
ymmärtävän yhteiskunnallisia realiteetteja sen sijaan, että heidät
leimataan psykoottisiksi? Tämä on noitavainojen logiikkaa, ei
2000-luvun länsimaista tiedettä.
Kuitenkin NHS:n artikkelissa päädytään toteamaan tutkimuksen olevan osa
kasvavaa todistusaineistoa kannabiksen käytön ja mielenterveysongelmien
välillä. Kun tätä tutkimusta kritiikistä huolimatta pidetään
korkeatasoisena niin millaista materiaalia se loppu on tuosta
kasvavasta todistusaineistosta? Leimaako koko tätä päättelyketjua
tarkoitushakuisuus? Mm. EMCDDA:n vuoden 2008 kannabisraportissa
esitellään tämä psykoositutkimuslinja mutta tuodaan sitten esille se,
että tätä teoreettista riskiä ei olla koettu käytännössä: EU:ssa ei ole
todettu mielenterveysongelmien lisääntymistä kannabiksen käytön
runsastumisen myötä. (http://www.emcdda.europa.eu/publications/monographs/cannabis)
Kannabis kiellettiin maailmanlaajuisesti vuoden 1961
huumausainesopimuksella ja kiellon perustana käytettiin kahta
argumenttia: 1. kannabis on yhtä vaarallista kuin heroiini tai
kokaiini; 2. kannabiksella ei ole minkäänlaista lääkinnällistä käyttöä.
Kiellon molemmat perustelut on kumottu vuosia ja vuosikymmeniä sitten
mutta kielto pysyy. Siksi tälle asioiden tilalle yritetään löytää uusia
perusteluja: kannabis on vaarallista, eihän sitä muuten olisi kielletty!
Cannabis use and psychosis
Monday June 2 2008
http://www.nhs.uk/news/2008/06June/Pages/Cannabisuseandpsychosis.aspx
Girls were more likely to have used cannabis
“Cannabis increases risk of psychosis in teens” is the headline in The
Daily Telegraph today. Users of cannabis have a “higher average number
of symptoms associated with a risk of psychosis”, the newspaper adds.
The results of a study of more than 6,000 young people in Finland also
suggests that teen users had a greater risk of the “prodromal”, or
warning symptoms, of psychosis than older users.
The study behind the stories is a cross-sectional study of adolescents
enrolled in a larger study. The design of this study means that it
cannot prove that the link between these warning symptoms and cannabis
use is a causal one. However, the findings add to the evidence that
there is a link between use of cannabis and mental health. It is
important that other factors which may affect the relationship are
taken into account in such studies; this is not an easy task. Before
definitive answers are found through research, it seems wise to avoid
smoking cannabis, not only because of the debate around mental health,
but also because of the well-known link between smoking and a host of
other diseases, including lung cancer and heart disease.
Where did the story come from? Dr Juoko Miettunen and colleagues from
the University of Oulu in Finland carried out this study. The research
was funded by the Academy of Finland, the Signe and Ane Gyllenberg
Foundation, the Sigrid Juselius Foundation and the Thule Institute at
the University of Oulu in Finland. It was published in the
(peer-reviewed) medical journal: the British Journal of Psychiatry.
What kind of scientific study was this? The study is a survey of young
people who are enrolled in a prospective cohort study with their
mothers. In 2001–2002, when the participants were aged about 15 or 16
years, they were invited to a clinical check-up where they were also
given a questionnaire to assess “prodromal” (early warning of
psychosis) symptoms and drug use.
Of the 9,340 children in the original cohort, 6,298 of them provided
answers to questions about cannabis use, and could be included in the
final analysis. The researchers used a shortened version (12 questions)
of a longer questionnaire (21 questions) called the PROD-screen to
assess prodromal symptoms of psychosis over the previous six months.
The questions asked about whether the subject had a feeling that
something strange or inexplicable is taking place in oneself or in the
environment; feelings that one is being followed or influenced in some
special way. From this, the researchers were able to discern which
children were “at risk of developing a psychotic disorder”.
"Cannabis use is associated with prodromal symptoms of psychosis in adolescence." Jouko Miettunen, lead author
The researchers also had access to information about the young people’s
early emotional and behavioural symptoms through questionnaires
completed by their teachers when the participants were eight years old.
They took these into account when analysing the relationship between
early symptoms of psychosis and drug use. They also considered other
factors that may have an effect on the relationship, such as gender,
parent social class, tobacco use and use of other drugs, as well as
parent substance misuse.
What were the results of the study? The majority of adolescents
reported that they never used cannabis (5,948/6,298). However, 352 (6%)
participants reported having used cannabis (once or more). Girls were
more likely than boys to have used cannabis. The study also found that
those who had tried cannabis had a higher mean number of prodromal
(early warning of psychosis) symptoms (3.11 v 1.88), and that compared
with those who had never used, those who had tried cannabis (once or
more) were twice as likely to have three or more prodromal symptoms (OR
2.23, 95% CI 1.70 to 2.94). This result took into account other factors
that may have had an effect (e.g. age, gender, smoking, parental
substance misuse etc.). The researchers also found that more intensive
cannabis use was more strongly associated with these symptoms.
What interpretations did the researchers draw from these results? The
researchers conclude that lifetime cannabis use is associated with the
incidence of early warning symptoms of psychosis.
What does the NHS Knowledge Service make of this study?
There are limitations to a study such as this that should affect the
interpretation of results, particularly where causation is being
claimed:
• As the researchers collected data on cannabis use
and early warning symptoms at one point in time, this is a
cross-sectional study. Due to their design, cross-sectional studies
cannot establish causation. At best, the researchers can say that
cannabis use is “associated with” or “linked to” the prodromal
symptoms. Other factors that may be involved become important when
interpreting results of studies such as these.
• Although the researchers took into account early
emotional and behavioural problems around age eight, they did not
account for mental problems that may have occurred between ages eight
and 16 years.
• Importantly, a positive “score” on the PROD-screen
questionnaire does not diagnose psychosis. It is used to indicate
whether a person is entering the period of early symptoms or changes in
function that may come before psychosis. However, even for this, the
score is not 100% accurate at predicting psychosis, or even proven as a
tool for diagnosing the prodrome. The researchers used a shortened form
of the original PROD-screen questionnaire (they reduced it from 21
questions to 12). It is unclear what effect this would have on the
overall accuracy of the screening test. If it was too inclusive, i.e.
there were a high number of false-positives, the relationship between
drug use and symptoms would have been overstated.
• The researchers grouped all adolescents who had
ever used cannabis into one category for analysis (i.e. they do not
differentiate between adolescents who have tried cannabis once and
those who are regular users).
Overall, this study points to an area that requires more research, but
because of its design, the study does not prove that cannabis causes
psychosis. Confirmation of the usefulness and accuracy of the
PROD-screen in predicting increased risk of psychosis will also be
important. When the findings are considered in light of a growing body
of evidence of a link between cannabis use and mental health problems
such as schizophrenia, it seems wise to limit the use of the drug. This
is not only because of considerations of the effects on mental health,
but also the well-established risks for cancer and other diseases that
are associated with smoking.
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