Relatively little actual data are available on the amount of marihuana, smoked per occasion or per day by current users in the United States. (McGlothlin, 1971, 1972). Estimates of the quantity of THC consumed are difficult because of the variability of potency as well as weight and size of the marihuana cigarette ("joint") and the degree of cleaning of stems and seeds from the dried leaves manicuring").

The analytic data available indicates most of the marihuana used in the United States is of Mexican origin and averages about I % THC per dry cleaned weight of marihuana (Lerner and Zeffert, 1968; Jones, 1971). Subjective ratings by experienced marihuana users appear to substantiate the data that marihuana containing 1% THC is of average quality (Jones and Stone, 1970; Weil et al., 1968).

Marihuana cigarettes are estimated (McGlothlin, 1971, 1972) to average about 0.5 g in weight and, therefore, contain about 5 mg of THC. Cigarettes used in the eastern states are generally smaller than those, rolled in the west (McGlothlin, 1971; New York Police Department, 1969, 1970)

Most data indicates that for the large majority of users one-half to one cigarette (2.5 to 5 mg THC) is sufficient to "get high" in intermittent moderate users, although often two or more cigarettes were smoked to achieve additional effect (Nisbet and Vakil, 1972; Shean and Fechtmann, 1971; McGlothlin et al., 1970- McGlothlin, 1972; Jones, 1971; Goode, 1970).

Current American daily users appear to consume one to two cigarettes per occasion (Jones, 1971) although some users estimate they smoke three to five cigarettes per occasion (McGlothlin et al., 1970). Goode (1971), however, found practically no relationship between amount required to get high and frequency of use (daily to less than monthly) or duration of use (less than two years to six or more years). In fact, the heavy and longer term users were less likely to require more "joints."

Thus, the estimated 15 mg THC for current daily users is about one-half that estimated for confirmed regular users 30 years ago in the United States (Mayor's Committee, 1944; Charen and Perelman, 1946) and one-third to one-fourth the median daily consumption of daily users in North Africa and India.

The maximum daily consumption of 10 cigarettes (50 mg THC) for current heavy U.S. marihuana smokers (Jones, 1971; McGlothlin, 1972) is about the same as the average amount consumed by daily chronic users in other countries, and about one-fourth or less of the maximum in these countries (Soueif, 1967; Sigg, 1963; Indian Hemp Drug Commission's Report, 1893-1894; Chopra, 1940; Chopra and Chopra, 1939).

Studies of American military in Vietnam (U.S. Congress, 1971; Colbach and Crowe, 1970; Forrest, 1970), and Germany (Tennant et al., 1971) described the daily use of quantities of hashish or potent marihuana comparable to amounts consumed by regular chronic users in other countries.

Experimental data appear to confirm these estimates of quantity of THC consumed. Isbell et al. (1967) and Jones (1971) found that most subjects reported a normal "high" after smoking 5-10 mg of THC. Meyer et al. (1971) found that a "very high" state was attained by ad libitum smoking of 3.12 mg THC by daily users and 3.78 mg THC by intermittent users.

In experiments by Johnson and Domino (1971), subjects were urged to smoke until they were as high as they had ever been on marihuana and felt they could not smoke any more. These subjects smoked from one to four cigarettes containing 8.7 mg of THC to reach this level of intoxication. The range was from 8.7 to 30 mg of THC with a mean of about 20 mg THC.

Intermittent and daily users were allowed to smoke marihuana on a free choice basis over a 21day period in studies by Mendelson et al. (1972). Each cigarette contained one gram of marihuana of approximately 2% THC content, or about 20 mg of THC.

Subjects were asked to rate their high on a 10 point scale with 10 corresponding to highest ever; five as moderately high and zero, no effect. Ratings for the daily user group ranged from zero to nine with an average of about six for all cigarettes rated. Individual means ranged f rom three to about seven. On almost all occasions, subjects in both groups smoked the entire cigarette.

Kiplinger et al. (1971) and Lemberger, et al. (1971) noted that daily long-term users were able to detect effects of the "high" at doses calculated to deliver as low as 5-7 micrograms/kg THC (equivalent to smoking about 100 mgs. of marihuana containing 1 % THC). Perhaps this explains the finding that many users are able to "get high" smoking US wild-growing marihuana containing front near zero to 0.5% THC (Lerner, 1969; Phillips et al., 1970; Fetterman et al., 1971).

Several ad libitum experiments were performed with marihuana of unknown composition (Williams et al., 1946; Siler et al., 1933) using "confirmed regular marihuana users" confined over a 39 and six-day period. The users, who generally consumed three cigarettes per day, under these rather artificial conditions of the, experiment consumed means of 17 (range nine to 26) and five (range one to 20) cigarettes per day respectively.

Miras and Coutsilinis (1970) reported recent experimental data on chronic Greek hashish users who routinely use, single smoked doses of hashish containing 100 mg of THC. Under ad libitum conditions, these users averaged 150-350 mg of THC per day over a 30-day period.

The subjects studied during a 21-day period of free choice Marihuana consumption by Mendelson et al. (1972) generally consumed all of one cigarette containing 20 mg of THC per smoking session. 'The subjects who were previously daily users were more likely during the experiment to consumer more, than one, cigarette per session than the, previously intermittent users.

Individual consumption by the intermittent users ranged from an average of about one-half to
six cigarettes per day (group mean three) while the daily users consumed an average of three-anda-half to nine cigarettes per day (group mean six-and-a-half). Reasons given by the subjects for the dramatic shift in the frequency of marihuana use included boredom, testing the limits of their endurance, demonstrating its harmlessness to the research staff, and subtle social pressure.