On study day 0 (before marijuana abstinence) and study day 1 (24 hours of marijuana abstinence), the current marijuana users did not differ from past heavy users or light users in the number of aggressive or non-aggressive responses they made. However, current marijuana users were significantly more aggressive on days 3 and 7 of marijuana abstinence compared to their pre-withdrawal levels of aggression and compared to the controls. By day 28, the number of aggressive responses from the current marijuana users was not different from their pre-withdrawal baseline levels or the controls (Figure).
These data demonstrate that abstinence from marijuana after chronic use is associated with increases in aggressive responding following provocation. Specifically, during the first week of abstinence, current marijuana users displayed levels of aggression that were significantly higher than before abstinence and higher than the levels displayed by matched controls.
Interestingly, the increases in aggressive responding followed a specific time course and then returned to pre-withdrawal levels after 28 days of abstinence. The transient nature of these changes is consistent with other reports of marijuana withdrawal.
The second study was designed to further characterize symptoms of marijuana withdrawal and to quantify their magnitude (Kouri and Pope, 2000). We used the same study entry criteria as in the first study and subjects were required to come to the laboratory every day to provide urine samples and to fill out a daily diary.
The items assessed in the daily diaries were: mood, appetite, sleep, anxiety, irritability, physical tension or agitation, physical symptoms, ability to concentrate, desire to use marijuana, and desire to resume using marijuana at the end of the study. The questions were presented on a 10-point Likert scale with the qualifiers "extremely low" at the zero end of the scale and "extremely high" at the 10-point end of the scale. We obtained pre-withdrawal baseline levels for all of the diary items via a personal interview with each subject before the beginning of the withdrawal period.
Thirty current marijuana users and 30 controls (16 former heavy users and 14 light users) participated in the study. Before the beginning of the abstinence period, the current marijuana users were not different from the former users or the light users on any of the items assessed in the diaries except for the ability to concentrate item. The current users reported a lower ability to concentrate than the controls. Interestingly, the former heavy users were not different from the light users on any of the diary scores during the course of the study. In contrast, the current users reported increases in irritability, anxiety, physical tension and physical symptoms, and decreases in mood and appetite starting on day 1 and peaking between days 7 and 10 of marijuana abstinence.
It is important to note that although, as a group, the current marijuana users experienced an increase in withdrawal symptoms compared to the controls, only 60% of the subjects in the current users group reported a change in symptoms of at least three points in magnitude. The fact that 40% of subjects who had used marijuana regularly for an average of 22 years did not report experiencing severe withdrawal symptoms during abstinence might suggest that physical dependence on marijuana is not as strong as that observed with other drugs of abuse. This may be due, at least in part, to the long half-life of THC. However, many subjects reported that when trying to remain abstinent in the past, the presence of withdrawal symptoms had played an important role in their relapse. Thus, alleviation of abstinence symptoms may contribute to the maintenance of daily marijuana use in chronic users.
Another significant finding is that after 28 days of marijuana abstinence, all of the symptoms returned to pre-withdrawal levels except for irritability and physical tension. It is possible that these two symptoms remained slightly elevated because they represented a premorbid characteristic of the current users and were not a result of marijuana withdrawal. If this is the case, the fact that the former users did not have elevated scores on these two items may reflect a characteristic that potentially differentiates individuals with a history of heavy marijuana use who have successfully stopped from individuals who continue to smoke regularly.