W. Murray Thomson, PhD, Professor of Dental Epidemiology and Public Health at Sir John Walsh Research Institute, et al., in their Feb. 6, 2008 study titled "Cannabis Smoking and Periodontal Disease Among Young Adults," published in the Journal of the American Medical Association, wrote:

Con

Burkhard Hinz, PhD, et al., of the Institute of Toxicology and Pharmacology at the University of Rostock in Germany wrote in a Dec. 25, 2007 article titled "Inhibition of Cancer Cell Invasion by Cannabinoids via Increased Expression of Tissue Inhibitor of Matrix Metalloproteinases-1" in the Journal of the National Cancer Institute:

"Prior knowledge
Treatment with cannabinoids had been shown to reduce the invasiveness of cancer cells, but the cellular mechanisms underlying this effect were unclear.

Study design
Cancer cells treated with combinations of cannabinoids, antagonists of cannabinoid receptors, and siRNA to tissue inhibitor of matrix metalloproteinases-1 (TIMP-1) were assessed for invasiveness, protein expression, and activation of signal transduction pathways.

Contribution
The expression of TIMP-1 was shown to be stimulated by cannabinoid receptor activation and to mediate the anti-invasive effect of cannabinoids.

Implications
Clarification of the mechanism of cannabinoid action may help investigators to explore their therapeutic benefit.

Limitations
The relevance of the findings to the behavior of tumor cells in vivo remains to be determined."
Dec. 25, 2007 Burkhard Hinz

[Note: Although this study was not conducted on humans, it was performed using human cells in a test tube which is why we have classified it under the “Human Studies” category.]

Pro

Margaret Haney, PhD, Associate Professor of Clinical Neuroscience at Columbia University, et al., in their Aug. 15, 2007 study titled "Dronabinol and Marijuana in HIV-Positive Marijuana Smokers: Caloric Intake, Mood, and Sleep," published in the Journal of Acquired Immune Deficiency Syndromes, stated:

Pro

Antonio W. Zuardi, PhD, Vice Director of the Department of Neurology at the University of São Paulo, et al. wrote in a Sep. 2006 article titled "Cannabidiol Monotherapy for Treatment-Resistant Schizophrenia" in the Journal of Psychopharmacology:

"Cannabidiol (CBD), one of the major products of the marijuana plant, is devoid of marijuana's typical psychological effects. In contrast, potential antipsychotic efficacy has been suggested based on preclinical and clinical data (Zuardi et al., 2002). In this report, we further investigated the efficacy and safety of CBD monotherapy in three patients with treatment-resistant schizophrenia (TRS)...

Efficacy, tolerability and side effects were assessed. One patient showed mild improvement, but two patients didn't show any improvement during CBD monotherapy. All patients tolerated CBD very well and no side effects were reported. These preliminary data suggest that CBD monotherapy may not be effective for TRS."
Sep. 2006 Antonio W. Zuardi

Con

Sonia Ständer, MD et al. wrote in a July 2006 article titled [Topical Cannabinoid Agonists: An Effective New Possibility for Treating Chronic Pruritus.] [Article in German] in the journal Hautarzt:

"BACKGROUND: Chronic, therapy-resistant pruritus often fails to respond to standard measures so new therapeutic approaches are needed. Recently, the expression of cannabinoid receptors on cutaneous sensory nerve fibers was described, so cannabinoid agonists seem a rational therapeutic option for pruritus...

RESULTS: In 14/22 patients a good antipruritic effect could be documented. The average reduction in itch was 86.4%. The therapy was well-tolerated by all patients; neither burning burn nor contact dermatitis was observed.

CONCLUSIONS: Topical cannabinoid agonists represent a new effective and well-tolerated therapy for refractory itching of various origins. Creams with a higher concentration may be even more effective with broader indications."
July 2006 Sonia Ständer

Pro

Jason Schiffman, PhD et al. wrote in a Jan. 2005 article titled "Symptoms of Schizotypy Precede Cannabis Use" in the journal Psychiatric Research:

"Findings suggest that regular cannabis users are significantly more prone to cognitive and perceptual distortions as well as disorganization, but not interpersonal deficits, than non-regular users and those who have never used.

Additionally, the onset of schizotypal symptoms generally precedes the onset of cannabis use. The findings do not support a causal link between cannabis use and schizotypal traits."
Jan. 2005 Jason Schiffman

Not Clearly Pro or Con

David M. Fergusson, PhD, Research Professor of the Department of Psychological Medicine at the University of Otago, et al. wrote in a Mar. 2005 article titled "Tests of Causal Linkages Between Cannabis Use and Psychotic Symptoms" in the journal Addiction :

"Regression models adjusting for observed and non-observed confounding suggested that daily users of cannabis had rates of psychotic symptoms that were between 1.6 and 1.8 times higher than non-users of cannabis....

The results of the present study add to a growing body of evidence suggesting that regular cannabis use may increase risks of psychosis.

The present study suggests that:
(a) the association between cannabis use and psychotic symptoms is unlikely to be due to confounding factors; and
(b) the direction of causality is from cannabis use to psychotic symptoms."
Mar. 2005 David M. Fergusson

Con

Maria L. de Ceballos, PhD, Researcher and Group Leade of the Department of Neural Plasticity at the Cajal Institute, Spain, et al. wrote in a Feb. 2005 article "Prevention of Alzheimer's Disease Pathology by Cannabinoids: Neuroprotection Mediated by Blockage of Microglial Activation" in the Journal of Neuroscience:

"Our results indicate that cannabinoid receptors are important in the pathology of AD [Alzheimer's Disease] and that cannabinoids succeed in preventing the neurodegenerative process occurring in the disease."
Feb. 2005 Maria L. de Ceballos

Researchers from the Movement Disorders Centre, Department of Neurology at Charles University, Prague, Czech Republic, wrote in their "Survey On Cannabis Use In Parkinson's Disease" published in the journal Movement Disorders :

"An anonymous questionnaire sent to all patients attending the Prague Movement Disorder Centre revealed that 25% of 339 respondents had taken cannabis and 45.9% of these described some form of benefit....

The late onset of cannabis action is noteworthy. Because most patients reported that improvement occurred approximately two months after the first use of cannabis, it is very unlikely that it could be attributed to a placebo reaction."
Sep. 2004 Movement Disorders

Pro

Ciaran M. Brady et al. wrote in an Aug. 2004 article titled "An Open-Label Pilot Study of Cannabis-based Extracts for Bladder Dysfunction in Advanced Multiple Sclerosis" in the journal Multiple Sclerosis:

"The majority of patients with multiple sclerosis (MS) develop troublesome lower urinary tract symptoms (LUTS). Anecdotal reports suggest that cannabis may alleviate LUTS, and cannabinoid receptors in the bladder and nervous system are potential pharmacological targets. In an open trial we evaluated the safety, tolerability, dose range, and efficacy of two whole-plant extracts of Cannabis sativa in patients with advanced MS and refractory LUTS."

"Urinary urgency, the number and volume of incontinence episodes, frequency and nocturia all decreased significantly following treatment (P <0.05, Wilcoxon's signed rank test). However, daily total voided, catheterized and urinary incontinence pad weights also decreased significantly on both extracts. Patient self-assessment of pain, spasticity and quality of sleep improved significantly (P <0.05, Wilcoxon's signed rank test) with pain improvement continuing up to median of 35 weeks.

There were few troublesome side effects, suggesting that cannabis-based medicinal extracts are a safe and effective treatment for urinary and other problems in patients with advanced MS."
Aug. 2004 Ciaran M. Brady

Pro

In their article "Psychoactive Substance Use and the Risk of Motor Vehicle Accidents," published in the journal Accident Analysis & Prevention, researchers K.L.L. Movig et al. wrote:

"The objective of this study was to estimate the association between psychoactive drug use and motor vehicle accidents requiring hospitalization...

The risk for road trauma was increased for single use of benzodiazepines and alcohol... High relative risks were estimated for drivers using combinations of drugs and those using a combination of drugs and alcohol. Increased risks, although not statistically significant, were assessed for drivers using amphetamines, cocaine, or opiates.

No increased risk for road trauma was found for drivers exposed to cannabis."
July 2004 Accident Analysis & Prevention

Mark A. Ware, Director of Research at the Magill University Health Centre (MUHC) Pain Clinic in Canada et al. wrote in a Mar. 2003 article titled "Cannabis Use for Chronic Non-Cancer Pain: Results of a Prospective Survey" in the journal Pain:

"There has been a surge in interest in medicinal cannabis in Canada. We conducted a questionnaire survey to determine the current prevalence of medicinal cannabis use among patients with chronic non-cancer pain, to estimate the dose size and frequency of cannabis use, and to describe the main symptoms for which relief was being sought...

Of the 32 subjects who used cannabis for pain, 17 (53%) used four puffs or less at each dosing interval, eight (25%) smoked a whole cannabis cigarette (joint) and four (12%) smoked more than one joint. Seven (22%) of these subjects used cannabis more than once daily, five (16%) used it daily, eight (25%) used it weekly and nine (28%) used it rarely. Pain, sleep and mood were most frequently reported as improving with cannabis use, and 'high' and dry mouth were the most commonly reported side effects. We conclude that cannabis use is prevalent among the chronic non-cancer pain population, for a wide range of symptoms, with considerable variability in the amounts used."
Mar. 2003 Mark A. Ware

Pro

Wilson M. Compton, MD et al., in their article "Prevalence of Marijuana Use Disorders in the United States: 1991-1992 and 2001-2002," published in the Journal of the American Medical Association (JAMA), the researchers wrote:

"Among the adult U.S. population, the prevalence of marijuana use remained stable at about 4.0% over the past decade. In contrast, the prevalence of DSM-IV [psychological classifications of disorders] marijuana abuse or dependence significantly increased between 1991-1992 and 2001-2002, with the greatest increases observed among young black men and women and young Hispanic men.

Further, marijuana use disorders among marijuana users significantly increased in the absence of increased frequency and quantity of marijuana use, suggesting that the concomitant increase in potency of delta-9-THC [one of the active ingredients in marijuana] may have contributed to the rising rates...

[M]arijuana abuse or dependence increased among marijuana users by 18% from 30.2% in 1991-1992 to 35.6% in 2001-2002...

The potency of delta-9-THC in confiscated marijuana from police seizure increased by 66% from 3.08% in 1992 to 5.11% in 2002...

Moreover, there was no systematic change in the frequency of marijuana use between 1991-1992 and 2001-2001...

Increasing rates of marijuana use disorders among marijuana users in the absence of increased quantity and frequency of use strengthens the argument that the increasing rates may be attributable, in part, to increased potency of marijuana."
May 2004 Journal of the American Medical Association

Not Clearly Pro or Con

John Macleod, PhD et al., in their article "Psychological And Social Sequelae of Cannabis and Other Illicit Drug Use by Young People: A Systematic Review of Longitudinal, General Population Studies," published May 15, 2004 in The Lancet, the researchers found:

"Available evidence does not strongly support an important causal relation between cannabis use by young people and psychosocial harm, but cannot exclude the possibility that such a relation exists.

The lack of evidence of robust causal relations prevents the attribution of public health detriments to illicit drug use. In view of the extent of illicit drug use, better evidence is needed."
May 15, 2004 John Macleod

"Results: With the exception of higher drug use in San Francisco, we found strong similarities across both cities. We found no evidence to support claims that criminalization reduces use or that decriminalization increases use.

Conclusions: Drug policies may have less impact on cannabis use than is currently thought."
May 2004 American Journal of Public Health

Diane Prentiss, M.A., MPH et al. wrote an article titled "Patterns of Marijuana Use Among Patients With HIV/AIDS Followed in a Public Health Care Setting" in the Jan. 2004 issue of Journal of Acquired Immune Deficiency Syndrome (JAIDS):

"Objectives: To examine prevalence and patterns of smoked marijuana and perceived benefit and to assess demographic and clinical factors associated with marijuana use among HIV patients in a public health care setting...

Results: Overall prevalence of smoked marijuana in the previous month was 23%. Reported benefits included relief of anxiety and/or depression (57%), improved appetite (53%), increased pleasure (33%), and relief of pain (28%). Recent use of marijuana was positively associated with severe nausea and recent use of alcohol and negatively associated with being Latino.

Conclusions: The findings suggest that providers be advised to assess routinely and better understand patients' indications for self-administration of cannabis. Given the estimated prevalence, more formal characterization of the patterns and impact of cannabis use to alleviate HIV-associated symptoms is warranted. Clinical trials of smoked and noncombustible marijuana are needed to determine the role of cannabinoids as a class of agents with potential to improve quality of life and health care outcomes among patients with HIV/AIDS."
Jan. 2004 Journal AIDS

John P. Zajicek, PhD of the Neurology Research and Clinical Trials Unit at the University of Plymouth et al. wrote in a Nov.2003 article titled "Cannabinoids for Treatment of Spasticity and Other Symptoms Related to Multiple Sclerosis (CAMS study): Multicentre Randomised Placebo-controlled Trial" in the journal Lancet:

"Background: Multiple sclerosis is associated with muscle stiffness, spasms, pain, and tremor. Much anecdotal evidence suggests that cannabinoids could help these symptoms. Our aim was to test the notion that cannabinoids have a beneficial effect on spasticity and other symptoms related to multiple sclerosis...

Interpretation: Treatment with cannabinoids did not have a beneficial effect on spasticity when assessed with the Ashworth scale. However, though there was a degree of unmasking among the patients in the active treatment groups, objective improvement in mobility and patients’ opinion of an improvement in pain suggest cannabinoids might be clinically useful."
Nov. 2003 John P. Zajicek

Not Clearly Pro or Con

An Oct. 2003 article in Nature Reviews - Cancer, "Cannabinoids: Potential Anticancer Agents," by Manuel Guzman, PhD, reported:

"Cannabinoids -- the active components of Cannabis sativa and their derivatives -- exert palliative effects in cancer patients by preventing nausea, vomiting and pain and by stimulating appetite.

In addition, these compounds have been shown to inhibit the growth of tumour cells in culture and animal models by modulating key cell-signaling pathways.

Cannabinoids are usually well tolerated, and do not produce the generalized toxic effects of conventional chemotherapies."
Oct. 2003 Nature Reviews - Cancer

Donald I. Abrams, MD et al. wrote in the article "Short-term Effects of Cannabinoids in Patients with HIV-1 Infection: A Randomized, Placebo-controlled Clinical Trial," (PDF) published Aug. 2003 in the journal Annals of Internal Medicine:

"Conclusions: Smoked and oral cannabinoids [marijuana] did not seem to be unsafe in people with HIV infection with respect to HIV RNA levels, CD4 and CD8 cell counts, or protease inhibitor levels over a 21-day treatment."

In a Feb. 2003 article published in the British Journal of Psychiatry (BJP) titled "Adolescent Precursors of Cannabis Dependence: Findings from the Victorian Adolescent Health Cohort," which studied students in Australia from 1992 through 1998 (when they were 20-21 years old), researchers noted the following:

"Results Of 1,601 young adults, 115 met criteria for cannabis dependence. Male gender, regular cannabis use and persistent cigarette smoking independently predicted cannabis dependence. Neither smoking severity nor persistent psychiatric morbidity independently predicted dependence. Regular cannabis use increased risk only in the absence of persistent problematic alcohol use.

Conclusions Weekly cannabis use marks a threshold for increased risk of later dependence, with selection of cannabis in preference to alcohol possibly indicating an early addiction process."
Feb. 2003 British Journal of Psychiatry

A study of 311 young adult twin pairs conducted by Michael T. Lynskey, PhD published Jan. 2003 in the Journal of the American Medical Association (JAMA) reported:

"Results: Individuals who used cannabis by age 17 years had odds of other drug use, alcohol dependence, and drug abuse/dependence that were 2.1 to 5.2 times higher than those of their co-twin, who did not use cannabis before age 17 years...

In particular, early access to and use of cannabis may reduce perceived barriers against the use of other illegal drugs and provide access to these drugs."
Jan. 2003 Journal of the American Medical Association

Not Clearly Pro or Con

In a study of over 50,000 Swedish conscripts, researchers Stanley Zammit, MD and Peter Allebeck, MD concluded as published Nov.23, 2002 in the British Medical Journal (BMJ):

"Cannabis was associated with an increased risk of developing schizophrenia in a dose dependent fashion both for subjects who had ever used cannabis, and for subjects who had used only cannabis and no other drugs.

Conclusions: Cannabis use is associated with an increased risk of developing schizophrenia, consistent with a causal relation. This association is not explained by use of other psychoactive drugs or personality traits relating to social integration."
Nov. 23, 2002 British Medical Journal

Con

A Sep. 2002 article in the journal Addiction, "Cannabis Use and Psychosocial Adjustment in Adolescence and Young Adulthood," stated:

"Cannabis use, and particularly regular or heavy use, was associated with increased rates of a range of adjustment problems in adolescence / young adulthood -- other illicit drug use, crime, depression and suicidal behaviours -- with these adverse effects being most evident for schoolaged regular users.

The findings reinforce public health concerns about minimizing the use of cannabis among school-aged populations."
Sep. 2002 Addiction

Anna H. Soderpalm, PhD et al. wrote in a July 2001 article titled "Antiemetic Efficacy of Smoked Marijuana: Subjective and Behavioral Effects on Nausea Induced by Syrup of Ipecac" in the journal Pharmacology, Biochemistry and Behavior:

"Although the public debate about the legalization of marijuana has continued for as long as 25 years, few controlled studies have been conducted to assess its potential medical benefits. The present study examined the antiemetic effect of smoked marijuana cigarettes (8.4 and 16.9 mg Delta(9)-tetrahydrocannabinol [THC]) compared to a highly potent antiemetic drug, ondansetron (8 mg) in 13 healthy volunteers. Nausea and emesis were induced by syrup of ipecac.

Marijuana significantly reduced ratings of 'queasiness' and slightly reduced the incidence of vomiting compared to placebo. Ondansetron completely eliminated the emetic effects of ipecac. These findings support and extend previous results, indicating that smoked marijuana reduces feelings of nausea and also reduces emesis in this model. However, its effects are very modest relative to ondansetron, and the psychoactive effects of marijuana are likely to limit its clinical usefulness in the general population."
July 2001 Anna H. Soderpalm

Pro

Donald P. Tashkin, MD, Director of the Pulmonary Function Laboratories at UCLA, in his article "Effects of Smoked Marijuana on the Lung and Its Immune Defenses: Implications for Medicinal Use in HIV-Infected Patients" published in the Journal of Cannabis Therapeutics (JCT), stated:

"Frequent marijuana use can cause airway injury, lung inflammation and impaired pulmonary defense against infection. The major potential pulmonary consequences of habitual marijuana use of particular relevance to patients with AIDS is superimposed pulmonary infection, which could be life threatening in the seriously immonocompromised patient.

In view of the immonosuppressive effect of THC, the possibility that regular marijuana use could enhance progression of HIV infection itself needs to be considered, although this possibility remains unexplored to date."
June 2001 Donald P. Tashkin

Con

Guy A. Cabral, PhD, in his article "Marijuana and Cannabinoids: Effects on Infections, Immunity, and AIDS"; published in the Journal of Cannabis Therapeutics (JCT), stated:

"The cumulative data obtained through cell culture studies using various immune cell populations extracted from animals or humans, together with those obtained using animal models of infection, are consistent with the proposition that marijuana and cannabinoids alter immune cell function and can exert deleterious effects on resistance to infection in humans....

However, few controlled longitudinal epidemiological and immunological studies have been undertaken to correlate the immunosuppressive effects of marijuana smoke or cannabinoids on the incidence of infections or viral disease in humans.

Clearly, additional investigation to resolve the long-term immunological consequences of cannabinoid and marijuana use as they relate to resistance to infections in humans is warranted."
June 2001 Journal of Cannabis Therapeutics