Research by a group of scientists studying the effects of heavy marijuana use suggests that withdrawal from the use of marijuana is similar to what is experienced by people when they quit smoking cigarettes. Abstinence from each of these drugs appears to cause several common symptoms, such as irritability, anger and trouble sleeping - based on self reporting in a recent study of 12 heavy users of both marijuana and cigarettes.

"These results indicate that some marijuana users experience withdrawal effects when they try to quit, and that these effects should be considered by clinicians treating people with problems related to heavy marijuana use," says lead investigator in the study, Ryan Vandrey, Ph.D., of the Department of Psychiatry at the Johns Hopkins University School of Medicine.

Marijuana is the most widely used illicit drug in the United States. Admissions in substance abuse treatment facilities in which marijuana was the primary problem substance have more than doubled since the early 1990s and now rank similar to cocaine and heroin with respect to total number of yearly treatment episodes in the United States, says Vandrey.

He points out that a lack of data, until recently, has led to cannabis withdrawal symptoms not being characterized or included in medical reference literature such as the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, (DSM-IV) or the International Classification of Diseases, 10th edition (ICD-10).

Since the drafting of the DSM-IV in 1994, an increasing number of studies have surfaced suggesting that cannabis has significant withdrawal symptoms. What makes Vandrey's recent study unique is that it is the first study that compares marijuana withdrawal symptoms to withdrawal symptoms that are clinically recognized by the medical community - specifically the tobacco withdrawal syndrome.

"Since tobacco withdrawal symptoms are well documented and included in the DSM-IV and the IDC-10, we can infer from the results of this comparison that marijuana withdrawal is also clinically significant and should be included in these reference materials and considered as a target for improving treatment outcomes," says Vandrey.

Vandrey added that this is the first "controlled" comparison of the two withdrawal syndromes in that data was obtained using rigorous scientific methods - abstinence from drugs was confirmed objectively, procedures were identical during each abstinence period, and abstinence periods occurred in a random order. That tobacco and marijuana withdrawal symptoms were reported by the same participants, thus eliminating the likelihood that results reflect physiological differences between subjects, is also a strength of the study.

Interestingly, the study also revealed that half of the participants found it easier to abstain from both substances than it was to stop marijuana or tobacco individually, whereas the remaining half had the opposite response.

"Given the general consensus among clinicians that it is harder to quit more than one substance at the same time, these results suggest the need for more research on treatment planning for people who concurrently use more than one drug on a regular basis," says Vandrey.

Vandrey's study, which appears in the January issue of the journal Drug and Alcohol Dependence, followed six men and six women at the University of Vermont in Burlington and Wake Forest University School of Medicine in Winston-Salem, N.C., for a total of six weeks. All were over 18 (median age 28.2 years), used marijuana at least 25 days a month and smoked at least 10 cigarettes a day. None of the subjects intended to quit using either substance, did not use any other illicit drugs in the prior month, were not on any psychotropic medication, did not have a psychiatric disorder, and if female, were not pregnant.

For the first week, participants maintained their normal use of cigarettes and marijuana. For the remaining five weeks, they were randomly chosen to refrain from using either cigarettes, marijuana or both substances for five-day periods separated by nine-day periods of normal use. In order to confirm abstinence, patients were given daily quantitative urine toxicology tests of tobacco and marijuana metabolites.

Withdrawal symptoms were self reported on a daily basis Monday through Friday using a withdrawal symptom checklist that listed scores for aggression, anger, appetite change, depressed mood, irritability, anxiety/nervousness, restlessness, sleep difficulty, strange dreams and other, less common withdrawal symptoms. Patients also provided an overall score for discomfort they experienced during each abstinence period.

Results showed that overall withdrawal severity associated with marijuana alone and tobacco alone was of similar frequency and intensity. Sleep disturbance seemed to be more pronounced during marijuana abstinence, while some of the general mood effects (anxiety, anger) seemed to be greater during tobacco abstinence. In addition, six of the participants reported that quitting both marijuana and tobacco at the same time was more difficult than quitting either drug alone, whereas the remaining six found that it was easier to quit marijuana or cigarettes individually than it was to abstain from the two substances simultaneously.

Vandrey recognizes that the small sample size is a limitation in this study, but the results are consistent with other studies indicating that marijuana withdrawal effects are clinically important.

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This study was conducted while Vandrey was a doctoral candidate at the University of Vermont. It was supported by grants from the National Institute on Drug Abuse.

Other researchers who contributed to this study are Alan Budney, Ph.D., of the University of Arkansas for Medical Studies, Little Rock; John Hughes, M.D., of the University of Vermont; and Anthony Ligouri, Ph.D., of Wake Forest University School of Medicine.