LONG-TERM CANNABIS TWIN STUDY

Does marijuana use have residual adverse effects on self-reported
health measures, socio-demographics and quality of life? A
monozygotic co-twin control study in men. Eisen SA et al.
Addiction (2002) 97:1137-44

Dear Colleagues,

This is another study with strong scientific rigour indicating that
long-term heavy cannabis use does not necessarily lead to
significant harm in later decades. This does not prove that cannabis
is safe by any means, but confirms that, at least for men who reach
maturity without problems, it is possible to smoke cannabis heavily
without adverse consequences when compared with identical twin
brothers who do not smoke cannabis.

The researchers from Seattle, Boston and St Louis gained access to
the 7000-strong Vietnam-era Twin Registry, finding 117 identical
twins in whom one member smoked cannabis heavily and the other
did not. Recent cannabis smokers (within one month) were
excluded, as were users of other illicit drugs (more than once
weekly) or subjects who had experienced alcohol withdrawal
symptoms (as a marker for dependency).

Of the 117 pairs who were eligible across America, 56 agreed to
participate (112 individuals who were paid $200 for their time).
There were no significant differences found in known health, race
or age characteristics of those who did not respond when compared
with those who did. An extensive questionnaire was taken
involving medical, mental and 'quality of life' details. No difference
was detected between partners who smoked heavily (minimum of
one day weekly for a year, mean 1085 days in life) when compared
with the non-smoking twin controls (less than five days ever). The
mean age of first cannabis use was 21 =B1 4 years.

This study excluded women and only involved men who had served
in the Vietnam war. There may be a 'non-responder' bias as well as
limited relevance to those whose general health would not qualify
them for military service. Thus while its findings are limited, it is
strong scientific evidence on the subject as it excluded those with
alcohol or other drug problems as causation 'confounders'. It is
also consistent with other long term studies of cannabis users (eg.
Tashkin 97, Gruber 97).

Many supporters of continued legal sanctions against cannabis rely
strongly on its dangers, both known and as yet unknown. It is a
paradox that although these dangers seem to be less than with
alcohol and tobacco, whatever their degree, they still persuade
strongly in favour of regulation rather than prohibition which
appears to have been ineffective as a form of control in most
communities, despite the enormous resources employed.

This report concludes, almost inescapably, yet very conservatively:
"The results of this study may be applicable to the ongoing
controversy in the US related to whether marijuana should remain a
Schedule I drug ... Thus it may be justifiable to investigate
marijuana's increasing list of possible therapeutic uses (Joy et al.
1999) under very carefully controlled medical supervision, without
exposing patients to a substantial risk of long-term adverse health
effects."


Date: Tue, 12 Nov 2002 1054 -0800
From: "D. Paul Stanford" <stanford@crrh.org>
Subject: 004 Long-term cannabis twin study
comments by Andrew Byrne ..