The drug effect of marihuana can only be realistically discussed within the context of who the user is, how long he has used, how much and how frequently he uses and what is the social context of the use. In general, for virtually any drug the heavier the use pattern, that is the longer the duration, the more frequently the use and the larger the quantity used on each occasion, the greater the risk for either direct or indirect damage.

Tolerance development is only one of a variety of occurrences which are related to the repetitive use of marihuana. Any discussion of drug effect must take into account the time period over which the drug is used (duration of use). This is necessary in order to detect cumulative effects or more subtle gradually-occurring changes. Of course, the issue of causality is quite complex because of the multitude of factors other than marihuana use that have a direct or indirect effect on the individual over a period of years.

For the purposes of this report, immediate or acute effects will refer to those drug effects which occur during the drug intoxication or shortly following it. Short-term or sub-acute will arbitrarily refer to periods of less than two years; long-term, from two to 10 years; and very long term (or chronic), greater than 10 years.

Frequency of use, will arbitrarily be designated in the following manner: experimental use refers to use of marihuana at least one time but not more than once a month; intermittent use refers to use more than once a month but not more than 10 times a month (several times a week) ; moderate use refers to use of the drug more than 10 times a month but not more than once a day; heavy use designates use more than once, daily and very heart use refers to use many times a day, usually with potent preparations (high THC content), producing almost continual intoxication so that the smoker's brain is rarely drug free.