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.