Length Of Reaction

The effects of marihuana can be detected within about 15 minutes after smoking (deep inhalations and maintaining inspirations). The peak reaction occurs about half an hour or so after smoking. Some effects may be noticeable several hours later, depending on the dose. Zinberg and Weil found that for doses of 0.5 or 2g (leaves), "observable effects ... were largely dissipated by three hours after the end of smoking." The length of the marihuana experience tends to vary with the individual and the dose. If the drug is eaten rather than smoked, the onset of symptoms occurs later, and the experience may be consiberably longer, (absorption into the bloodstream takes much longer).

The most consistently appearing physical effects are an increased or unstable pulse rate, and suffusion of the conjunctiva, (reddening due to dilatation of the blood vessels). Blood pressure, respiratory rate, pupillary size and threshold for elicitation of the knee jerk are more or less unaffected. Blood sugar levels, possible changes in which were previously thought to be associated with reported effects of hunger, are in fact unchanged. Other reported effects are dryness of the mouth, diuresis, numbness or coldness of the extremities. Some sleepiness, nausea or headache may also occur. (See experimental reports of Isbell el al., Ames, Zinberg and Weil. The doses used were equivalent to about 2g of marihuana leaves smoked.)

A number of workers have studied the effects of marihuana on various performance tests. Some early experiments are recorded in the 'Report of the Mayor's Committee on Marihuana' (New York 1944), cited by Edwards, and by Clark and Nakashima. These suggested that simple functioning, such as reaction time and tapping, are not impaired except by large doses. However, more complex psychomotor functions may, they state, show impairment at comparatively low doses.

More recently, working with naive subjects on doses equivalent to 1.5-4g crude marihuana, Clark and Nakashina conclude that effects on "complex (choice) reaction time and on a digit code memory task were most consistently impaired", though there were still marked individual differences. One problem, noted here and elsewhere, isoccasioned by the frequent waxing and waning nature of the experience, which results in varying impairment on the same dose.

Zindberg and Weil's investigation demonstrates the important differences between the reactions of naive and regular users. Three tests were used. The first was a continuous performance test lasting five minutes, in which the subject had to press a button whenever a particular letter appeared in a sequence of letters being flashed across a screen. The test was repeated with a strobe light flickering at 50 cycles per second. Normal subjects make few errors on this test, but it has been found that lack of sleep and some drugs can adversely affect performance on it. The second test was a digit symbol substitution test, a simple test of cognitive function-page 7ing which required the subject to match symbols to numbers. The third test was a 'pursuit rotor' test, measuring muscular co-ordination and attention; it involved keeping a stylus in contact with a small spot on a moving turntable.

There was no significant change for either group on the first test, with or without the flickering strobe light. On both the digit symbol and pursuit rotor tests the performance was good, actually improved on these tests after smoking marihuana.

Estimations of time intervals are often inaccurate after smoking marihuana, there being a strong tendency to estimate the time as being much later than it is, and a feeling that events are taking much longer than they really are.

Immediate recall may also be impaired. Ames, using naive subjects, notes that conversations became bizarrely disconnected because of this. However, if reminded of a previous statement, the subject could pick up the thread again. Direct questioning invariably elicited prompt and relevant replies, but if the subjects were left to themselves to pursue a train of thought, the difficulty of immediate recall manifested itself. One of Zinberg and Weil's naive subjects, after 2g of marihuana, commented "I would keep forgetting what I was doing, especially on the continuous performance test, but somehow, every time an 'x', [the critical letter] came up, I found myself pushing the button."

Some of the gaps in existing experimental work are obvious. Few subjects are being used; they are generally all young (20-30), and tend to be members of rare groups—students, prison inmates, ex-opiate addicts', regular marihuana users etc. Only some effects e.g. suffusion of the conjunctiva after moderate doses, could be expected to be uniformly present in the reactions of subjects taken from many diverse groups.

A greater range of tests need to be carried out with a wider range of doses. It seems likely, however, that the usual amount smoked recreationally is comparable to the above experimental doses. The Chopras found that in their Indian sample, heavy users rarely smoke more than 10g a day of ganja (flowering tops and resinous stems from female plant). (cited by Murphy.) Heavy users in the States use similar amounts, perhaps 5-10 marihuana cigarettes a day. Most marihuana smoked, however, is taken on a more casual basis and the quantities are correspondingly smaller. (The amount of hashish reportedly taken by heavy users in e.g. India and N. Africa, would result in doses of perhaps 5-10 times more THC than would be taken in by heavy marihuana smokers in the West.)

The range of tests, and the circumstances under which they are conducted, are more serious limitations on making evaluations for practical situations. Is it safe, for example, to drive a car two hours after smoking, say three or four joints? The evidence suggests that the results might not be disastrous, but obviously care and some control must be exercised (as for alcohol and other drugs). More complicated tasks, less contingent on the laboratory setting, should be investigated. Many users claim that the effects of marihuana are more easily suppressed than are those of alcohol. (see e.g. Becker, Zinberg and Weil.) It is important to know at what level of complexity, effective task performance becomes impaired. Variations in performance with different levels and duration of use should be further investigated.