Measurement of Cannabis Effects

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3.2.1. Physiological 3.2.1.1. Cardiovascular

Periodic monitoring of heart rate and blood pressure during cannabis administration is recommended because of the expected effects of tachycardia and orthostatic hypotension. Monitoring should begin before cannabis administration, to provide a baseline, and continue until values have returned to baseline levels. Measurements should be obtained more frequently during periods of expected maximum cannabis effect (which will vary by route of administration), then less frequently as the cannabis effect subsides. Heart rate can be efficiently monitored using an electrocardographic (ECG) chest lead. This also provides information about heart rhythm (although cannabis administration is not commonly associated with cardiac arrhythmia). Blood pressure can be measured with a standard clinical sphygmomanometer.

3.2.1.2. Neurological

Gross motor coordination can be assessed with standard clinical neurological tests, such as finger-to-nose, one-leg stand, and observation of gait, and by computerized body sway devices. Tremor can be assessed by observation using standardized rating scales, or with electronic devices (accelerometers).

3.2.2. Psychological 3.2.2.1. Subjective Effects

Cannabis and other drugs of abuse produce psychoactive effects, i.e., drug-induced changes in mood and feelings mediated by the central nervous system. Such changes in mood and feelings are termed subjective because they are not directly observable. Because of common verbal learning histories, subjects can generally agree in their responses on validated questionnaires when describing subjective states produced by psychoactive drugs. Subjective effects are also termed self-report effects because they can only be inferred from subjects' responses to questionnaires or other measurement instruments.

The acute subjective effect most commonly reported by experienced cannabis users is the pleasant, euphoric state known as the drug "high." The intensity of this and other subjective effects (e.g., sedation, hunger, anxiety, clarity of thinking) can be assessed by two different types of questions. Visual analog scales (VAS) require subjects to place a vertical mark along a 100-mm line anchored by "not at all" on the left and "extremely" on the right. Responses are measured in mm from 0 to 100. A Likert scale requires subjects to choose from among several categories of intensity, e.g., "not at all," "mild," "moderate," and "severe." Responses are scored as ascending integers starting with 0. The simplest scale is dichoto-mous, i.e., the effect is scored as either present (1) or absent (0). For both types of questions, the higher the score, the greater the intensity of the subjective effect. Cannabis-specific questions should be interspersed with nonspecific questions to minimize response bias (see Note 7).

The marijuana (M) scale is a self-report instrument specifically designed to measure cannabis intoxication. It is a subscale (12 true-false statements) of the larger Addiction Research Center Inventory (ARCI) (24,25) (see Note 8). Higher scores indicate greater intensity of cannabis intoxication. The ARCI contains several other subscales that are less reliably sensitive to acute cannabis effects (see Note 9).

Peak subjective effects typically occur during or immediately after smoking a single cannabis cigarette and gradually decline over several hours. To capture the complete time course of subjective effects, measurements should be repeated every 10 to 15 min during the first hour after smoking and every 20 to 30 min thereafter.

3.2.2.2. Psychomotor Performance

Psychomotor performance refers to motor (movement) skills, eye-hand coordination, and speed of response to visual or auditory stimuli (often referred to as reaction time). Acute cannabis administration typically impairs psychomotor performance, with higher doses producing greater impairment (for reviews, see refs. 26-28). Numerous standardized tests measure various aspects of psychomotor performance (see Note 10). Impaired performance is observed within 30-45 min after smoking cannabis and persists for several hours. Some studies have documented performance decrements 12-24 h after smoking cannabis (29).

3.2.2.3. Attention and Cognition

Attention and cognition are broad psychological terms that include many specific functions involving higher order cognitive processing. Attentional processes involve searching, scanning, and detecting visual or auditory stimuli for brief or extended periods of time. These can be categorized as focused, selective, divided, or sustained attention (30). Cognitive processes involve learning, memory, problem solving, and reasoning skills. Such distinctions are somewhat arbitrary because any memory task requires attention and memory skills, as well as other cognitive resources. Acute cannabis administration impairs many aspects of attention and cognition, as described below and reviewed elsewhere (26-28) (see Note 11). As with psychomotor performance, cognitive impairment can last for up to 24 h after smoking cannabis (31).

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