The Commission broadly defines public health concerns as all health problems which affect people en masse and are thereby difficult to treat on a traditional physician-to-patient basis. This category would include social and economic dependence and incapacity. A health problem which spreads to other susceptible members of the society cannot be controlled by the individual physician. This view coincides with the concept of preventive medicine, recognizing that all public health problems must be dealt with on both an individual and societal level.

To illustrate, the increasing incidence of deaths due to lung cancer subsequent to chronic, heavy tobacco usage is a major public health concern. In this instance, prevention of smoking and ascertaining the cause of the malignancies, rather than the individual treatment of each case by a physician, define the public health dimension. A major concern exists because the population at risk is large and growing, and the risk of harm is great.

In addition to the risk of large numbers of the populace being affected, the issue of contagion must also be examined. Unlike infectious diseases such as influenza and smallpox, where the person affected " catches" the ailment unintentionally, those individuals who use marihuana choose to come into contact with it. The contagion model is relevant only insofar as social pressure from proselytizing friends and social contacts play a role in spreading the use of the, drug. This dimension exists with marihuana, as well as alcohol and tobacco.

After assessing the potential harm to the individual and society, the size of the population at risk and the contagion aspect, society must determine the nature of the control mechanism used to deal with the problem, and how nine]) of its health resources, manpower and facilities will be allocated to meet the perceived threat to the public health. Therefore, an analysis of the relative risk of marihuana use must be undertaken. We must examine not only the effects of the drug on the individual but also determine which groups are at risk and why.

Practically all substances consumed by man are potentially dangerous to the physical or mental health of the individual if used irresponsibly or by particularly sensitive persons. Certain substances are sufficiently complex in their effects that societal control is necessary to reduce risk, for example, fluorides added to the water supply, prescription drugs, and food additives. The degree of concern and control varies, depending on relative public health dangers.