The measurement of cue-elicited cannabis craving in studies testing human research volunteers is described in Subheadings 3.1.1.-3.1.7. This includes (1) recruiting cannabis users who are not seeking treatment for their cannabis use, (2) obtaining written informed consent from research participants, (3) training participants in completion of the MCQ, (4) cue presentation to elicit a craving response, (5) measuring the craving response with the MCQ and physiological recording devices, and (6) debriefing participants before they are discharged from the laboratory.
The use of cannabis-experienced participants who are not seeking treatment for their cannabis use is critical. There are no proven methods for long-lasting craving reduction; thus, it would be unethical to elicit craving in individuals who were trying to reduce or quit using cannabis. A thorough screening procedure, including a history of cannabis use (see Note 1), will generally ensure that appropriate participants are enrolled in the study.
As in any study involving human research volunteers, an Institutional Review Board (IRB) must approve the study protocol and consent from. When the IRB office has released the stamped consent form to the investigator, participants can be enrolled in the study. The consent form consists of a description of study procedures, any risks that are involved, monetary compensation if any, and investigators' contact information should participants have questions or concerns. When a participant understands all aspects of the study and potential risks, the investigator and participant sign the consent form; a copy is given to the participant.
The only aspect of the MCQ with which participants might be unfamiliar is the 7-point Likert scale that is used to record responses to each statement of the MCQ. For this reason, it is important that all participants be given standard instructions before the study begins (see Note 2). Table 1 presents the 12-item MCQ; its scoring is discussed in Note 3.
Various types of cues have been used to elicit craving in drug users (7). We have recently used imagery scripts that were recorded on compact disc and presented auditorially to participants via headphones (6). Scripts described situations that depicted a person experiencing either a desire to smoke cannabis (low-craving script), a strong desire to smoke (high-craving script), or made no mention of smoking cannabis (no-craving script). All scripts were written with positive emotional tone (see Note 4 for sample scripts). Participants are instructed to close their eyes while they listen to the scripts, to imagine themselves in the scene, and to continue imagining until they hear a tone. Each imagery trial consists of 120 s of baseline physiological recording, 60 s of script presentation, and 30 s of continued imagery. A rest period of 5-10 min should
12-Item Marijuana Craving Questionnaire
1. Smoking marijuana would be pleasant right now.
2. I could not easily limit how much marijuana I smoked right now.
3. Right now, I am making plans to use marijuana.
4. I would feel more in control of things right now if I could smoke marijuana.
5. Smoking marijuana would help me sleep better at night.
6. If I smoked marijuana right now, I would feel less tense.
7. I would not be able to control how much marijuana I smoked if I had some here. STRONGLY DISAGREE_:_:_:_:_:_:_STRONGLY AGREE
8. It would be great to smoke marijuana right now.
9. I would feel less anxious if I smoked marijuana right now.
10. I need to smoke marijuana now.
11. If I were smoking marijuana right now, I would feel less nervous.
12. Smoking marijuana would make me content.
separate each imagery trial, and the three imagery conditions (no, low, and high craving) should be randomized across participants to avoid the confounding of a condition order effect.
3.7.5. Measurement of Craving
The MCQ should be administered before the study begins (baseline) and immediately after the imagery trial because craving levels peak at this time.
The MCQ can be administered using paper and pencil forms or using a computerized version. Advantages to the paper and pencil method are that it requires no equipment other than the form, a pencil, and perhaps a clipboard; however, it will have to be scored by hand, which introduces the possibility of human error. A computerized version presents the MCQ items one at a time, and participants respond using the mouse or keyboard to move a cursor to indicate their response. Repeated administration of the MCQ should continue for sufficient time to observe a complete time course. Responses to tobacco imagery cues have been shown to remain at peak levels for at least 15 min (8).
3.1.6. Physiological Recording (Optional)
Typically, the primary measure in craving studies is self-reported responses on questionnaires such as the MCQ. However, certain physiological measures have reliably shown changes during cue-elicited craving episodes in the laboratory. Heart rate and skin conductance are two of the most reliable effects (7). Participants should be connected to any physiological recording devices during a training session to allow them to become familiar with the equipment. Experimental sessions should begin by connecting participants to the equipment, which can then record responses during the entire session.
At the conclusion of a session, participants should undergo a debriefing session to reduce potentially heightened craving. The debriefing session entails 10-15 min of guided progressive relaxation. This procedure involves alternatively tensing and relaxing the major muscle groups of the body (e.g., neck, shoulders, arms, legs). As the various muscle groups are tensed and relaxed, the person is encouraged to note the difference between muscle tension and relaxation. Relaxation has been shown to reduce craving in the laboratory (6,9,10). Participants should not be released from the laboratory until their self-reported cravings at the end of the relaxation session are less than or equal to their craving levels at the start of the session.
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