National Commission on Marihuana and Drug Abuse
Investigations of Very Heavy, Very Long-Term Cannabis Users
Proving a causal relationship between the use of any substance and an associated
illness or condition is extremely difficult. Ideally, prospective longitudinal studies on
large populations of both substance users and nonusers matched for socioeconomic and
psycho-cultural variables should be performed for many years in order to detect subtle or
cumulative effects. Unfortunately, the enormous expenditures of research effort and
finances that would be required for a large scale investigation of this nature are
prohibitive.
Consequently, carefully designed and controlled, clinical and epidemiological studies
of very heavy, very long-term cannabis users in foreign countries must be relied upon to
provide important data on possible effects because these populations are not obtainable in
the United States.
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