Netherlands National Drug Monitor - Research and Documentation ...

2.7 Illness and deaths
Illness
Increasingly, cannabis use is associated with mental problems.
• Evidence is mounting that cannabis use increases the risk of later psychotic disorders
(CAM, 2008).
• The risk increases with the frequency of use.
• Individuals with a prior history of psychotic symptoms are at greater risk of developing
psychosis following cannabis use than those without a prior history.
• It is possible that genetic factors play a role in this. There are indications that people
with a certain variant (Val/Val) of the COMT-gene, which is involved in the breakdown
of the receptor dopamine in the brain are extra susceptible to developing a
psychosis, particularly if they have commenced cannabis use at a young age (Caspi
et al., 2005).
• Between six and ten percent of all new annual cases of psychotic disorders can be
attributed to cannabis use.
• Dutch-grown weed contains relatively little cannabidiol (CBD) compared to THC
content. CBD counteracts some of the effects of THC, and may possibly have a
protective effect against the development of psychoses.
• Research into the relationship between cannabis use and the onset of other mental
problems, such as anxiety disorders depression, has yielded a less consistent picture
(Moore et al., 2007).
• Users can become dependent on cannabis, particularly with frequent use and an early
age of onset. Often other personal and environmental factors play a role as well.
Chronic, heavy use of cannabis is also associated with other health risks.
• Heavy, chronic cannabis use probably increases the risk of respiratory problems and
lung cancer. This is because cannabis smoke contains toxic combustion and incineration
substances. In addition, the manner of smoking a joint (prolonged, deep inhalation),
results in increased absorption of these substances in the airwaves, compared to
smoking a cigarette.
- Increased likelihood of infection appears only to occur in cannabis smokers whose
immune system is already compromised.
- In the Netherlands, cannabis is generally mixed with tobacco. Tobacco smoke causes
the same respiratory symptoms.
- Since the majority of cannabis smokers quit the habit after some time, thus limiting
the amount of dangerous substances that they inhale, compared to tobacco
smokers who often smoke for longer periods, it is expected that the contribution
of smoking cannabis to the incidence of cancer will remain limited.
• To date it has not been established that cannabis use during pregnancy causes serious
birth defects. Any congenital defects that have been found are slight effects on cognitive
development at a later stage of development.
54 Netherlands National Drug Monitor - NDM Annual Report 2009