Schaffer Library of Drug Policy

Marihuana: A Signal of Misunderstanding

Acute Effects of Marijuana (Delta 9 THC) - Effects on Mentation and Psychomotor Performance

US National Commission on Marihuana and Drug Abuse

Table of Contents
I. Marihuana and the Problem of Marihuana
Origins of the Marihuana Problem
The Need for Perspective
Formulating Marihuana Policy
The Report
II. Marihuana Use and Its Effects
The Marihuana User
Profiles of Users
Becoming a Marihuana User
Becoming a Multidrug User
Effects of Marihuana on the User
Effects Related to Pattern Use
Immediate Drug Effects
ShortTerm Effects
Long Term Effects
Very Long Term Effects
III. Social Impact of Marihuana Use
IV. Social Response to Marihuana Use
V. Marihuana and Social Policy
Drugs in a Free Society
A Social Control Policy for Marihuana
Implementing the Discouragement Policy
A Final Comment
Ancillary Recommendations
Legal and Law Enforcement Recommendations
Medical Recommendations
Other Recommendations
Letter of Transmittal
Members and Staff
History of Marihuana Use: Medical and Intoxicant
II. Biological Effects of Marihuana
Botanical and Chemical Considerations
Factors Influencing Psychopharmacological Effect
Acute Effects of Marihuana (Delta 9 THC)
Effects of Short-Term or Subacute Use
Effects of Long-Term Cannabis Use
Investigations of Very Heavy Very Long-Term Cannabis Users
III. Marihuana and Public Safety
Marihuana and Crime
Marihuana and Driving
Marihuana - Public Health and Welfare
Assessment of Perceived Risks
Preventive Public Health Concerns
Marihuana and the Dominant Social Order
The World of Youth
Why Society Feels Threatened
The Changing Social Scene
Problems in Assessing the Effects of Marihuana
Marihuana and Violence
Marihuana and (Non-Violent) Crime
Summary and Conclusions: Marihuana and Crime
Marihuana and Driving
History of Marihuana Legislation
History of Alcohol Prohibition
History of Tobacco Regulation
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The Report of the National Commission on Marihuana and Drug Abuse

Acute Effects of Marihuana

(Delta 9 THC)


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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