Pubdate: Mon, 19 Sep 2005
Source: Ottawa Citizen (CN ON)
Copyright: 2005 The Ottawa Citizen
Author: Jim Grose
Bookmark: (Cannabis - Canada)


Re: We need the truth about marijuana, Sept. 15.

Letter-writer L.S. Davidson proposes more research on the long-term effects 
of marijuana use. She specifically proposes a data base, with hospital 
psychiatrists collecting data on patient use and illness.

There are several problems with this approach.

First, we would only have data on people who have used marijuana and are 
seeking treatment. What about all those who have used marijuana but are not 
suffering from mental illness? What about all those who have used 
marijuana, are suffering from mental illness but are not seeking treatment? 
To compute rates we would need the total number of users and the number who 
suffer from mental illness.

Even so, this would not reveal any cause-effect relationship. Smoking 
marijuana may predispose a person to mental illness. Mental illness may 
predispose a person to smoke marijuana. Which came first, the chicken or 
the egg?

Additionally, a third unknown factor may predispose a person to both mental 
illness and smoking marijuana; that is, both are effects and neither is the 
cause of the other.

In fact, the necessary data are already collected by Statistics Canada. The 
Canadian Community Health Survey collects cross-sectional data on, among 
other things, illicit drug use, psychological well-being and contacts with 
mental health professionals. The National Population Health Survey collects 
similar data.

Why reinvent the wheel?

Jim Grose,


Research Analyst,

Applied Research and Analysis Directorate,

Health Canada 
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