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Major Studies of Drugs and Drug Policy
Marihuana, A Signal of Misunderstanding - Table of Contents

The Report of the National Commission on Marihuana and Drug Abuse

Acute Effects of Marihuana

(Delta 9 THC)


EFFECTS ON MENTATION AND PSYCHOMOTOR PERFORMANCE

Characteristically, intoxication with psychoactive materials effect psychomotor and mental functions. It is apparent from the subjective assertions of users and a wide range of experimental studies that marihuana is no exception (Clark and Nakashima , 1968; Clark et al., 1970; Dornbush and Freedman, 1971; Hollister and Gillespie, 1970; Manno et al., 1970; Mayor's Committee, 1944; McGlothlin et al., 1971; Melges et al., 1970; Meyer et al., 1971; Weil and Zinberg, 1969; Weil et al., 1968; Volavka et al., 1971; Galanter et al., 1972; Kiplinger et al., 1971; Mendelson et al., 1972; Dornbush et al., 1971).

Psychomotor tasks which have been tested include tapping speed, handwriting and free-hand writing and free handdrawing, simple and complex reaction time, pursuit rotor and tracking tasks and continuous performance tests. Cognitive tasks frequently tested are simple arithmetic problems, serial addition or subtraction, fine judgment tasks, 'digit-symbol substitution test, digit-code memory, reading comprehension, speech or verbal out-put, forward and backward digit spans, goal directed complex serial subtractions and additions to reach a set end sum, and short-term or immediate memory functions.

In general, Kiplinger et al. (1971) have clearly demonstrated that the degree of impairment is dose related and varies in degree during the period of intoxication exerting its maximal effect at the peak intoxication.

Naive subjects commonly demonstrate greater decrement in performance than experienced users but report less subjective effect (Weil et al., 1968). Experienced users appear to better compensate to the effect of the drug especially for ordinary performance at lower doses (Clark and Nakashima, 1968; Clark et al., 1970; Crancer et al., 1969; Jones and Stone, 1970; Meyer et al., 1971; Weil and Zinberg, 1969; Jones, 1971; Mendelson et al., 1972). Performance of simple or familiar tasks (i.e. simple reaction time) during intoxication is minimally effected. However, on unfamiliar or complex tasks (i.e., complex reaction time), performance decrements occur (Weil and Zinberg, 1969; Dornbush et al., 1971; Moskowitz et al., 1970).

Performance decrements are further enhanced when verbal tasks are performed during delayed auditory feedback (Kiplinger et al., 1971). Also marked individual differences in performance are noted between similar subjects. (Clark and Nakashima, 1968; Clark et al., 1970; Manno et al., 1970; Kiplinger et al., 1971). A cyclical waxing and waning of the intensity of the intoxication and concomitant performance occurs periodically (Clark et al., 1970; Melges et al., 1970).

Finally, when subjects concentrate on the task being performed at "normal social high," objective evidence of intoxication is not apparent and the individual may perform better than when drug free (Rodin and Domino, 1970; Mendelson et al., 1972).

Obviously, these observations raise practical doubts regarding the intoxicated individuals' ability to function at jobs requiring memory, concentration, and organization of thinking.


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