Articoli scientifici
10/06/2011

Il rischio di decesso in una coorte di soggetti segnalati dalle forze dell’ordine per consumo di Cannabis. Risultati di uno studio longitudinale.

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Introduction

Cannabis is themost widely used illicit substance in the world, and an estimated 159 million people used it over the course of the last year.1 In Europe one adult in five has tried it at least once, with a prevalence of recent use that ranges from 1% to 11.2% in various countries.2

Consumption is greater in urban than in rural areas, is higher in subjects under 35 years of age and inmales, starts at around 15 years of age and increases until 23 years of age and then decreases, is more common among people who smoke cigarettes, and is diffuse not only in nightclubs and discos, atmusical events and at other events specifically aimed at young people, but also among working people.3-6

With regard to their negative health effects, the acute toxicity of cannabinoids is very low because they do not cause respiratory depression like opiates do.7 Some revisions of the scientific literature have been recently published with the specific aim of defining the principle noxious effects of cannabis use.8-11 Evidence of chronic effects is limited, partly because it comes fromobservational studieswhich often do not adequately control for possible confounding factors and in which the direction of the causal relationship is not often clear.Considering these limits, the most probable effects on health of continued use are: dependence syndrome, chronic bronchitis,weakening of respiratory functions, cancer of the respiratory system, cardiovascular problems and psychotic disorders - these last few above all among habitual consumers with personal or family history of similar symptoms.8 In the research conducted on the general population use is associated with psychotic symptoms and the association persists even after adjusting for other factors.12

Although no direct effect onmortality was found, it is notable that cannabis is the secondmost frequent psychotropic drug, after ethyl alcohol, to be connected to traffic accidents.13-17 Even occasional use diminishes psychomotor performance and notably increases risk, even though epidemiological studies have not proven its relationship with risk of traumatic events.18

It is interesting to study health outcomes in the cannabisusing population, but the population is elusive and can be only studied with anonymous methods that do not permit follow-up. Because Italy has a systemthat sends subjects found in possession of cannabis for personal use to the Prefect, the archives of the prefecture can be used as a sample of the population of users.

In Italy anyone who uses, imports, buys or in any way possesses narcotic or psychotropic substances for personal use in amounts above the daily average as defined by law, is reported to the Prefect and then subject to civil sanctions. Reported users are called upon to explain, in person, the reasons for the behavior. On these occasions a Drug Addiction Control Force (DACF), established at each prefecture, assists the Prefect in this process.

This study is designed to study the mortality rate of subjects reported to theDACF for cannabis possession for personal use. General mortality trends will be estimated from 1990 until 2004, aswill the specific contribution of various causes of death to general mortality and temporal trends, and the association of possible predictors and mortality will be analyzed.

Materials and methods

The cohort wasmade up of 2,511 subjects, 90.9%male, average age 24.5 years. Follow up continued until 31.12.2004 for 99.8%of the subjects or until the date of death (four subjects lost to follow up), the at-risk person years were 12,686, the first death occurred in 1996.

Regarding the data quality, marital status was known for 34.8% of the cases, occupational status for 34.4%, and educational degree for 32.3%.

The enrolled subjects were residents of themetropolitan area of Bologna, and had been reported by the police force to the Prefect (Prefettura) for cannabis detention between 01.01.1990 and 31.12.2004.

Life status was verified at themunicipality (commune) of the subject’s latest residence. The cause of death was verified at themortality archives of the local health authority of residence using ICD-IX codes (International Classification of Disease and Causes of Death, IX revision).

The four subjects who were lost to follow up were included in calculating person years until the date they moved from their last known residence. To evaluate the temporal trend of mortality in the period under study standardized rates were calculated by age with directmethods and relative confidence intervals of 95%(Standard: Italy 1991, genders combined).

To compare mortality rates of reported drug users with those of the general population we calculated the standardizedmortality ratios (SMR) and relative confidence intervals at 95% specifically for cause and gender (Standard: Bologna Province).

The main data were taken from police department files (date of the report, date of birth, gender), whereas demographic data were recorded during the interview (educational degree, occupational status, and marital status).

To identify people who had already been treated for drug dependence, the cohort was linked with the clinical archive of the public treatment centers for drug addiction (PTC) in the metropolitan area of Bologna between 01.01.1990 and 31.12.2004 and the results were separated into PTC clients (subjects in treatment at a PTC in the metropolitan area of Bologna, all heroin users) and non-PTC clients (subjects not treated at a PTC in the metropolitan area of Bologna: illicit drug use besides cannabis and possible treatment at a PTC outside of our region were both unknown).

To evaluate mortality in relation to the date the subject was reported to the authorities, three time periods were defined: <1996 (AIDS), 1996/2000 (harm reduction), 2001/2004 (current phase).

Data analyses were calculated using the software statistical program STATA 8.0.

Results

Table 1 reports subjects’ characteristics at the time of the violation: 10.2% were caught before 1996, 51.3% between 1996/2000, and 38.4% after 2000.

191 subjects (7.6%) presented themselves for treatment at a PTC and according to the clinical chart, all of them were heroin users. The clinical chart listed 13.2% as having been incarcerated, all of them were heroin users, 34.0% also used cannabis, 29.8% used cocaine, 8.9% used benzodiazepines, and 11.0% also abused alcohol.

Mortality distribution

During the follow-up period 41 deaths were observed among men and 4 among women. Amongmen, 26.8%of the deaths were fromtraffic accidents, 36.6%fromoverdose, 9.8%from AIDS, and 4.9% from suicide. The four deaths reported among the women were respectively due to overdose, traffic accident, suicide and cirrhosis.

Among the PTC clients themortality rate was 8.04 (95%CI 4.32-11.77) andmost of the deaths were due to opiates overdose (4.50; 95%CI 1.69-7.30), AIDS or suicide; among non PTC clients themortality rate was 8.77 (95%CI 0.08-17.48) and most deaths were from traffic accidents or unspecified overdose (1.07; 95% CI 0-2.16).

SMR

An excess ofmortality was observed for all causes in the cohort compared to the general population, both among PTC clients and non-clients (Table 2). Among PTC clients the highest and most statistically significant SMRs were for overdose, suicide, and AIDS. Among non PTC clients there was an excess for traffic accidents and overdose.

Standardized rates and analyses of temporal trends

For non PTC clients the standardized mortality rate was higher in women; the most common causes of death for the entire period were all other causes excluding traumas and overdoses (Table 3).

PTC clients had higher mortality rates for overdose, AIDS and suicide than non clients and lower rates for the other causes of death.

For non PTC clients themortality rate was higher for subjects who were reported to the Prefect before the year 2000 (2.25 per thousand person years before 1996, 2.70 between 1996/2000) than the successive period (1.0 after 2000), while for PTC clients the rate increased after 2000 (17.10 per one thousand person years before 1996, 14.41 between 1996/2000, 32.05 after 2000).

Discussion

While numerous studies have documented greater risk of death for heroin and cocaine addicts, and there is scientific evidence of a causal relationship between the use of those substances and mortality, for cannabis users however, this relationship has not been demonstrated and life-style and behavioral factors should be studied to find a possible connection.19-22 In a study involving structured interviews of 45,540 men in the SwedishNational Service in 1969/70 with a follow up in 1983, there was no evidence of higher mortality risk for cannabis users, but a higher risk was correlated to life style factors (trouble with the police, or contact with juvenile social services), family situations (divorced parents), high consumption of alcohol and psychiatric problems.21

In a study of 65,171 subjects, 57% female, interviewed between 1979 and 1985 relative to life style and use of psychotropic drugs, with a follow up in 2001, Sidney reports greatermortality risk fromAIDS amongmale cannabis users. The author interprets this as a distortion due to the lack of controlling for confounders related to bisexual and homosexual behaviors. It also showed a greater risk associated with smoking tobacco with respect to current marijuana use, among both men and women.22

Our study has a few objective limits that suggest particular caution in interpreting the results.The data utilized were those available from police reports and then recorded on computerized charts, a process that could have been done in different ways over time. In addition, it was not possible to analyze age at first use, duration or average dose.The possible use of other substances over timewas available only for subjects that received treatment at a public drug treatment center, all heroin addicts.

Reported drug users represent only some of the consumers that make up the “underworld” of psychotropic substance abuse, and the greater risk ofmortality also reflects “selection” criteria related to the people who were caught by the authorities (who goes out at night, who frequents certain locations or company, who travelsmore, whomakes themselvesmore visible, who is more likely to infringe on the rules, etc.).Other possible biases should be considered determined by the fact that the reported drug user, to avoid incurringmore serious legal problems, claims to be the consumer of the confiscated substance, even if he or she only uses occasionally, consumes other substances or intended to sell the drugs.This weighs on the results, which tend to overestimate the average risk of death.

The health effects showed in the study cannot be exclusively attributed to cannabis, as frequent use is associated with that of other psychotropic substances, both legal and illegal. Cannabis, with current patterns of use, probably has a small tomoderate impact on public health if compared to alcohol, tobacco, heroin and methamphetamines and, with the exception of traffic accidents, most of the harm is experienced by a limited number of subjects who become regular consumers of the substance.23

On the whole, excess mortality was observed among males and females reported for cannabis possession for personal use compared to the general population. This excess remains, above all for traffic accidents, even when non PTC clients are distinguished from PTC clients.

Sixty-three percent of overdoses occurred among non PTC clients, an amount that invites the hypothesis that some of them also consumed other substances, heroin in particular, and only a small number of them were treated at a public drug treatment center.

With regard to traffic accidents, there is general consensus in the published literature on the capacity of hallucinogens, cannabinoids, narcotics, solvents, psycho-stimulants and opiates to debilitate drivers,17 and a dose/effect correlation has been documented that demonstrates the relationship between cannabis and traffic accidents.24 On one hand, traffic accidents seem to be a specific risk for habitual consumers of cannabis; on the other these alsomay be deaths attributable to dangerous life styles ascribable in part to the cohort selection criteria.

Conclusions

The results of the study show an elevated risk of death for subjects reported by authorities for cannabis possession for personal use, a percentage of whom could not be quantified in this study, most likely also consumed other substances, and a very few which presented themselves for treatment at a public drug treatment center.

It should be pointed out that, not having information on the principle confounders or on common factors, the data reported in the article are only descriptive and preliminary and should be considered with caution. In particular, the effect of cannabis “alone” can be assumed weaker than what is presented, and the effect presented should be interpreted as the result of a combination of environmental and behavioral factors that today in Italy accompany the use of cannabis.

All cases reflect a very complex phenomenon with a notable impact on the population that should not be simplified by focusing interventions exclusively on controlling and preventing consumption.

Conflitti di interesse dichiarati: nessuno

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