Recent Cannabis Use Research Articles

The consequences of substance use among gay and bisexual men: A Consensual Qualitative Research analysis

Substance use is common among gay/bisexual men and is associated with significant health risks (e.g. HIV transmission). The consequences of substance use, across the range of substances commonly used, have received little attention. The purpose of this study is to map participant's beliefs about the effects of substance use to inform prevention, health promotion and clinical interventions. Participants were interviewed about experiences regarding their substance use and recruited through medical and sexual health clinics. Data were collected though a consumer panel and individual interviews. Responses regarding perceived consequences of substance use were coded using Consensual Qualitative Research (CQR) methodology. Most participants reported lifetime use of alcohol, cannabis, stimulants and amyl nitrite, and recent alcohol and cannabis use. A wide range of themes were identified regarding participant's thoughts, emotions and behaviours (including sexual behaviours) secondary to substance use, including: cognitive functioning, mood, social interaction, physical effects, sexual activity, sexual risk-taking, perception of sexual experience, arousal, sensation, relaxation, disinhibition, energy/activity level and numbing. Analyses indicated several consequences were consistent across substance types (e.g. cognitive impairment, enhanced mood), whereas others were highly specific to a given substance (e.g. heightened arousal post amyl nitrite use). Prevention and interventions need to consider the variety of effects of substance use in tailoring effective education programs to reduce harms. A diversity of consequences appear to have direct and indirect impacts on decision-making, sexual activity and risk-taking. Findings lend support for the role of specific beliefs (e.g. expectancies) related to substance use on risk-related cognitions, emotions and behaviours.

Geographical clustering of cannabis use: Results from the New Zealand Mental Health Survey 2003–2004

BackgroundIn epidemiology, it always has been important to study local area patterns of disease occurrence. New methods to quantify local area and household clustering of disease emerged late in the 19th century and were refined during the 20th century. Nonetheless, multi-level models to estimate local area clustering of illegal drug use did not appear until the 1990s, and to date, there is just one study with estimates of local neighbourhood clustering of cannabis use, based on a United States sample. Here, seeking the first replication of that single prior study, we estimate the degree to which cannabis use might cluster within neighbourhoods of New Zealand (NZ), and we also study higher level clustering and suspected individual-level determinants of recent cannabis use. MethodsA national probability community sample (n=12,992) of adults aged 16 years or more with standardized assessment of cannabis use. Alternating logistic regression produced estimates for cannabis clustering. ResultsIn NZ, use of cannabis was common: 41.6% had ever used it and 13.1% had used it in the past year. There was clustering within the smallest local areas (pairwise odds ratio=1.3–1.5) but not within larger government districts (PWOR=1.02). Age, male sex, ethnicity, education, and marital status were all associated with cannabis use, but did not account for observed clustering. ConclusionsNeighborhood clustering of recent cannabis use has emerged in New Zealand, as in the US. Standard individual-level characteristics explain only some of this clustering. Other explanations must be sought, perhaps including personal networks and local supply.

Cannabinoid Concentrations in Spot Serum Samples 24-48 Hours After Discontinuation of Cannabis Smoking

A blood concentration of tetrahydrocannabinol (THC) in the low nanograms-per-milliliter range is often claimed to result from drug use more than 24-48 h previously. The present investigation determined concentrations of cannabinoids in blood collected at least 24 h from smoking in an in-patient setting. During sampling, distinctive effects due to drug use could not be observed. The randomly collected samples from heavy (n = 16, > 1 joint/day), moderate (n = 15, < or = 1 joint/day), and light (n = 6, < 1 joint/week) users of cannabis were analyzed for THC, 11-hydroxy-THC (OH-THC), and free 11-nor-9-carboxy-THC (THCCOOH) by gas chromatography-mass spectrometry as well as for glucuronidated THCCOOH by liquid chromatography-tandem mass spectrometry. THC was detectable in 9, 6, and 1 samples from heavy, moderate, and light users, respectively. Although cannabinoid concentrations were overlapping between groups, there was a trend towards higher concentrations of both conjugated and free THCCOOH in regular users compared to occasional users. The present findings appear to indicate that low levels of THC, or of THC along with OH-THC, may not unequivocally prove a very recent use of cannabis.

Daily Cannabis Use: A Novel Risk Factor of Steatosis Severity in Patients With Chronic Hepatitis C

Steatosis is highly prevalent in patients with chronic hepatitis C (CHC) and has been reported to increase fibrosis and reduce the rate of viral eradication. Two recent studies indicate that endocannabinoids promote experimental steatosis via activation of hepatic CB1 receptors. We therefore investigated the impact of cannabis smoking on steatosis severity during CHC. A total of 315 consecutive patients with untreated CHC undergoing liver biopsy were included. Detailed histories of recent cannabis, alcohol, and tobacco use were recorded. Steatosis, activity, and fibrosis stage were assessed by 2 pathologists according to METAVIR. Marked steatosis was defined as >/=30%. Patients were categorized as cannabis nonusers (63.5%), occasional cannabis smokers (12.4%), or daily cannabis smokers (24.1%). Multivariate analysis identified 6 predictors of marked steatosis: daily cannabis use (odds ratio [OR], 2.1; 95% confidence interval [CI], 1.01-4.5]), activity grade >/=A2 (OR, 2.1; 95% CI, 1.0-4.3), genotype 3 (OR, 5.4; 95% CI, 2.6-11.3), hyperglycemia or diabetes (OR, 5.1; 95% CI, 1.8-15.0), body mass index >27 kg/m(2) (OR, 2.1; 95% CI, 1.0-4.3), and serum HCV RNA load (OR, 1.7; 95% CI, 1.0-2.9). Upon adjustment of HCV genotype (3 vs non-3) or alcohol intake (<30 g/day vs >/=30 g/day), marked steatosis was more frequent in daily cannabis users compared with occasional users and nonusers (P = .03 and P = .008, respectively). Our results identify daily cannabis smoking as a novel independent predictor of steatosis severity during CHC and strongly argue for a steatogenic role of the cannabinoid system. Cannabis use should be discouraged in patients with CHC.

The Effects of Cannabis Use on Wages of Prime‐age Males*

AbstractThis paper uses a data set collected among inhabitants of Amsterdam, to study whether wages of prime‐age male workers are affected by cannabis use. The analysis shows that recent cannabis use has a negative effect on wages. The size of the wage effect depends on the age of onset. The earlier the start of cannabis use the larger the negative wage impact.

Roadside sobriety tests and attitudes toward a regulated cannabis market

BackgroundMany argue that prohibition creates more troubles than alternative policies, but fewer than half of American voters support a taxed and regulated market for cannabis. Some oppose a regulated market because of concerns about driving after smoking cannabis. Although a roadside sobriety test for impairment exists, few voters know about it. The widespread use of a roadside sobriety test that could detect recent cannabis use might lead some voters who currently oppose a regulated market to support it. In contrast, a question that primes respondents about the potential for driving after cannabis use might lead respondents to be less likely to support a regulated market.MethodsPhone interviews with a national sample of 1002 registered voters asked about support for a regulated cannabis market and support for such a market if a reliable roadside sobriety test were widely available.ResultsIn this sample of registered voters, 36% supported a regulated cannabis market. Exploratory chi-square tests revealed significantly higher support among men and Caucasians but no link to age or education. These demographic variables covaried significantly. Logistic regression revealed that gender, ethnicity, and political party were significant when all predictors were included. Support increased significantly with a reliable roadside sobriety test to 44%, but some respondents who had agreed to the regulated market no longer agreed when the sobriety test was mentioned. Logistic regression revealed that ethnicity and political affiliation were again significant predictors of support with a reliable sobriety test, but gender was no longer significant. None of these demographic variables could identify who would change their votes in response to the reliable roadside test.ConclusionIncreased awareness and use of roadside sobriety tests that detect recent cannabis use could increase support for a regulated cannabis market. Identifying concerns of voters who are not Caucasian or Democrats could help alter cannabis policy.

Factors associated with the use of solvents and cannabis by medical students

Introduction The use of alcohol and other drugs among medical students has been a theme of growing interest and concern on the part of researchers, teaching institutions and medical associations since the decade of the 1960's. Objective Recent use of alcohol, tobacco, tranquillisers, amphetamines, cannabis, organic solvents, and cocaine among 456 medical students was surveyed. Method Assessment was done by means of a self-report questionnaire according to World Health Organisation guidelines. Results Among medical students, after alcohol and tobacco, cannabis and solvents are the most frequently used psychoactive substances. As such, they were the most deeply analysed drugs in this study. Factors associated with the recent use of cannabis and solvents were established by logistic regression. Living with parents or a companion appeared as a protective factor for the use of cannabis. However, being male and regularly participating in the activities at the campus Sports Association showed as risk factors for the use of both cannabis and solvents. Discussion Concepts and misconceptions concerning protective and risk factors must be discussed in the light of cultural and circumstantial interferences. Harm reduction strategies should be seriously considered.

Cannabis et accidents de la voie publique : résultats des dernières études françaises

The clarification of the mechanisms of action of cannabis and its effects on motor and cognitive functions, the results of previous studies performed on driving simulators and closed or open-road driving trials, are important criteria for highlighting the increased risk of road crashes for drivers after a recent use of cannabis. In addition epidemiological studies allow to measure the magnitude of the problem. A survey of French epidemiological studies performed from 1999 to 2004, as well as the data of THC distribution in tissues studies performed on man and animal allowed us to draw a number of conclusions. The risk of road crash after a recent use of cannabis is increased by more than 2.4 in all studies. The prevalence of cannabis use in drivers involved in a road crash has dramatically increased during the last years. For methodological reasons (a too high threshold for THC positivity, a too long time delay between accident and blood sampling), the annual number of fatal cases induced by a cannabis use was likely underestimated. This assessment is consistent with recent data which indicate that THC could be still present in brain while absent in blood. A positivity threshold for THC in blood of 0.5 ng/mL would be more appropriated. So, all recent French studies highlighted that a recent use of cannabis impairs driving ability and that it would be advisable to intensify roadside testing for drugs of abuse.

Review of Biologic Matrices (Urine, Blood, Hair) as Indicators of Recent or Ongoing Cannabis Use

Especially for cannabinoids, analytical procedures for the verification of recent use and generally for the assessment of the extent of drug abuse are of interest in clinical and forensic toxicology. For confirmation of abstinence, urine analysis seems to be a useful tool. Serial monitoring of THC-COOH to creatinine ratios can differentiate between recent drug use and residual THC-COOH excretion (THC-COOH/creatinine ratio > or = 0.5 compared with previous specimen ratio). For an assessment of the extent of cannabis use, the determination of free and bound THC-COOH and especially of THC and 11-OH-THC glucuronides are suggested as useful but need further confirmation. Blood analysis is preferred for the interpretation of acute effects after cannabis abuse. The cannabis influence factor (CIF) was demonstrated as a better tool to interpret the concentrations of THC and its metabolites in blood in forensic cases and therefore it was proposed to assume absolute driving inability because of cannabis intoxication from a CIF > or = 10. Additionally, a higher CIF is indicative of a recent cannabis abuse. Also discrimination between occasional use of cannabis and regular drug consumption is possible by analysis of THC-COOH in blood samples because of the long plasma half-life of THC-COOH and its accumulation in the blood of frequent cannabis consumers. In routine tests, blood samples have to be taken within a prescribed 8-day-period, and a THC-COOH concentration >75 ng/mL is assumed to be associated with regular consumption of cannabis products, whereas plasma THC-COOH concentrations <5 ng/mL are associated with occasional consumption. In contrast to other illicit drugs, hair analysis lacks the sensitivity to act as a detector for cannabinoids. THC and especially the main metabolite THC-COOH have a very low incorporation rate into hair and THC is not highly bound to melanin, resulting in much lower concentrations in hair compared with other drugs. Additionally, THC is present in cannabis smoke and also can be incorporated into the hair only by contamination. For the determination of the main metabolite THC-COOH in the picogram or femtogram per milligram range, which indicates an active consumption, special analytical procedures, such as GC/MS/MS techniques, are required.

Illicit and traditional drug use among ethnic minority adolescents in East London

To explore ethnic variations in the use of illicit and traditional drugs, and the association of indicators of acculturation with drug use among an ethnically diverse representative sample of early adolescents in East London. A cross-sectional questionnaire survey. Confidential questionnaires were used to assess 2789 male and female pupils in years 7 and 9, aged 11-14 years old, from a representative sample of 28 secondary schools in East London. In total, 10.8% reported having ever tried illicit drugs and 7.3% reported ever using cannabis. Compared with white British adolescents, cannabis use in the previous month was significantly higher amongst black Caribbean adolescents. Lifetime cannabis use was significantly higher amongst black Caribbean and mixed ethnicity young people, but was lower amongst Bangladeshi, Indian and Pakistani adolescents. Living in UK for 5 years or less markedly reduced the risk of lifetime and recent cannabis use when controlled for ethnicity and social class. Glue or solvent use was reported in 3.2% of adolescents, with use significantly higher amongst Bangladeshi young people. Lifetime paan use was reported by 14.1% of the sample, and was almost completely confined to South Asian or mixed ethnicities. Ethnic differences in illicit drug use were found in the study population, and significant differences were found between ethnic groups often identified as 'black.' Further research is needed in understanding cultural-specific risk and protective factors in different ethnic groups, and the importance of cultural identity in mediating health risk behaviors. The high use of paan and glue/gas/solvents by Bangladeshi young people poses an unappreciated public health problem that may require targeted interventions.

Cannabis use, sport practice and other leisure activities at the end of adolescence

Purpose: To study the relationship between cannabis use, sports practice and other leisure activities during adolescence, as a test for the sociological theory of deviant opportunities. Methods: A sample of 12,512 French adolescents aged 18 responded to an anonymous self-reported questionnaire in March 2001. Three logistic models (for occasional, recent and regular cannabis use) were estimated for girls and boys separately. Results: Outings and other peer-oriented activities were strongly correlated with cannabis use but this relationship depended on which levels of use were considered. Occasional use was more common among respondents who participated in many different outdoor activities. Regular use was associated with a more selective lifestyle, focusing on music-oriented outings and time spent at a friend’s home in the evening. Conclusions: Our results provided empirical support for the theory of deviant opportunities. Changing patterns of lifestyle associated with transition from initiation to higher levels of use may reveal a shift from opportunities of cannabis use provided by a wide range of activities to specific activities chosen for their convenience to cannabis use. Further research will need to investigate how drug use is shaped by lifestyle, and conversely, how drug use reshapes lifestyle.

Substance use by adolescents in cape town: prevalence and correlates

Purpose The work reported in this paper was supported by grants from the World Health Organisation Programme on Substance Abuse, the United Nations Development Programme, the South African Medical Research Council, and the Medical Faculty Research Committee of the University of Cape Town. To document the prevalence rates for use of cigarettes, alcohol, and cannabis among high school students in Cape Town, and to investigate whether use of these substances is associated with a set of hypothesized psychosocial correlates. Methods A multistage sampling procedure produced a sample of 2930 students in grades 8 and 11 at 39 high schools in Cape Town, who completed a self-administered questionnaire. The questionnaire contained items about whether the students had used various substances and that addressed the potential correlates of interest. We calculated prevalence rates with 95% confidence intervals and constructed a set of generalized estimating equations of use in the past month of cigarettes, alcohol, or cannabis on the hypothesized correlates. Results The prevalence rates for previous month (recent) use of cigarettes, alcohol, and cannabis were 27%, 31%, and 7%, respectively. Rates were low for black females. Recent use of each of the substances was significantly associated with the number of days absent and the number of years lived in a city. Repeating a grade was significantly associated with previous month use of cigarettes and alcohol by colored (derived from Asian, European, and African ancestry) students and alcohol use by black grade 8 students (race classifications “colored” and “black” are as defined by the repealed population Registration Act of 1950). Not being raised by both parents was significantly associated with cigarette smoking by black and colored students, alcohol use by colored students, and cannabis use by female students. It was inversely associated with cigarette use by black students. Conclusions It is necessary to identify the factors that protect black female adolescents from substance use. It is important to address demographic factors such as race classification and gender analytically if one is to avoid obscuring differences among groups.

Cognitive functioning of long-term heavy cannabis users seeking treatment.

Cognitive impairments are associated with long-term cannabis use, but the parameters of use that contribute to impairments and the nature and endurance of cognitive dysfunction remain uncertain. To examine the effects of duration of cannabis use on specific areas of cognitive functioning among users seeking treatment for cannabis dependence. Multisite retrospective cross-sectional neuropsychological study conducted in the United States (Seattle, Wash; Farmington, Conn; and Miami, Fla) between 1997 and 2000 among 102 near-daily cannabis users (51 long-term users: mean, 23.9 years of use; 51 shorter-term users: mean, 10.2 years of use) compared with 33 nonuser controls. Measures from 9 standard neuropsychological tests that assessed attention, memory, and executive functioning, and were administered prior to entry to a treatment program and following a median 17-hour abstinence. Long-term cannabis users performed significantly less well than shorter-term users and controls on tests of memory and attention. On the Rey Auditory Verbal Learning Test, long-term users recalled significantly fewer words than either shorter-term users (P =.001) or controls (P =.005); there was no difference between shorter-term users and controls. Long-term users showed impaired learning (P =.007), retention (P =.003), and retrieval (P =.002) compared with controls. Both user groups performed poorly on a time estimation task (P<.001 vs controls). Performance measures often correlated significantly with the duration of cannabis use, being worse with increasing years of use, but were unrelated to withdrawal symptoms and persisted after controlling for recent cannabis use and other drug use. These results confirm that long-term heavy cannabis users show impairments in memory and attention that endure beyond the period of intoxication and worsen with increasing years of regular cannabis use.

Concordance between verbal report and urine screen of recent marijuana use in adolescents.

This study compared the concordance of self-report for recent marijuana use with results obtained from urine drug screen. The sample consisted of adolescent sons of fathers with DSM-III-R lifetime substance use disorder (SUD) [high average risk (HAR); N= 75] and sons of fathers with no Axis 1 psychiatric or SUD [low average risk (LAR); N= 125]. To avoid recall bias, and to ensure that the timeframe for accurate detection was restricted to promote accuracy, urine drug screen results were compared to self-reported marijuana use during the prior 48 h using an interview format. The HAR group of adolescents reported a higher rate of recent cannabis use and also had a higher rate of cannabis detection as measured in urine. The two groups did not differ with respect to either over or under-reporting marijuana use. Overall, of 19 participants who obtained positive urine cannabis results, six (31.5%) verbally denied that they used marijuana within the previous 2 days. Among the 181 participants who obtained a negative urine drug screen, 20 subjects (11.5%) inaccurately asserted that they had used marijuana within the prior 2 days. In total, 13% of the participants (26/200) inaccurately reported recent cannabis use. These results underscore the need for caution in interpreting the results of self-report methods documenting the prevalence of drug use among youth.

CORRELATES AND 6-MONTH OUTCOMES FOR CO-OCCURRING CANNABIS USE IN RURAL AND URBAN AT-RISK DRINKERS

We know little about the functional correlates of recent cannabis use when such use is additional to an “alcohol disorder” in non-treatment populations. We report on data from a prospective study of a large probability community survey of 733 at-risk drinkers in six Southern U.S. states (Alabama, Arkansas, Georgia, Louisiana, Mississippi, and Tennessee) conducted from 1995 to 1996. Twenty-one percent reported cannabis use during the past six months at the baseline interview. These cannabis users were significantly less likely to be married, employed, or a high school graduate (p<.05). They were also more likely to have a diagnosis of “antisocial personality disorder” or “panic disorder.” Recent cannabis users also reported more negative consequences of their alcohol use, including more frequent recent diagnoses of an “alcohol disorder,” legal difficulties associated with their drinking, and more social consequences attributed to drinking. At the six-month follow-up interview, negative alcohol outcomes were associated with concurrent cannabis use, including higher frequency and quantity of alcohol consumption, greater frequency of recent “alcohol abuse” and “dependence,” and greater social consequences of drinking. These results all point to substantially poorer functioning and experiences of individuals with concurrent at-risk alcohol and cannabis use. We suggest that cannabis use may be a marker for greater impairment associated with at-risk drinking. [Translations are provided in the International s Section of this issue.]

The Relationship of Neuropsychological Functioning to Measures of Substance use in an Adolescent Drug Abusing Sample

The purpose of this research was to investigate the relationship between recent and long term substance use on adolescents' neuropsychological functioning. Subjects were 77 adolescents who were referred for outpatient treatment for drug and conduct problems. Subjects were administered the Luria-Nebraska Neuropsychological Battery-III, structured interviews to assess substance use, and urine tests. Subjects were divided into neuropsychologically impaired and nonimpaired groups. Results indicated no significant group differences for: self-reports of lifetime use of alcohol, cannabis, and hard drugs; self or collateral reports of recent (past 30 days) use of alcohol, cannabis, and hard drugs; or urinalysis detection of alcohol, cannabis, and hard drugs. Correlations between these dependent measures of substance use and neuropsychological functioning were also nonsignificant (all ps >. 05). Although neuropsychological impairment was observed for some subjects in this sample, it was unrelated to their cannabis, hard drug, or alcohol use. These results are consistent with those found in the adult literature, given the relatively short period of time that these youth have used such substances. However, given the severity of their absolute levels of substance usage, they may be at greater risk for developing future neuropsychological problems, related directly to the ingestion of alcohol and illicit drugs, and to their secondary effects (e.g., head traumas, malnutrition).

Neuropsychological correlates of urine toxicology results

1. 1. The present study evaluated neuropsychological differences among 4 groups of men and women, aged 15 to 61 years. The groups were defined on the basis of urine toxicology screens indicating recent cocaine (n = 12), cannabis (n = 14), or multiple drug (n = 7) use, or no such use (n = 21). 2. 2. The Wechsler Adult Intelligence Scale-Revised (WAIS-R), the Trail Making Tests, and the Porteus Maze Test were administered to all subjects. 3. 3. Analyses revealed no significant differences between the groups in age, gender composition, or in the proportion of group members with personal histories of alcohol/drug abuse or dependence, or Anti-Social Personality Disorder. 4. 4. The cocaine positive group exhibited statistically significant impairments in Verbal IQ, as well as on Information, Vocabulary, Comprehension, Picture Completion, and Trails B subtests. The other experimental groups did not differ from the urine negative group.

Cannabis and schizophrenia — A follow-up

To explore ethnic variations in the use of illicit and traditional drugs, and the association of indicators of acculturation with drug use among an ethnically diverse representative sample of early adolescents in East London.A cross-sectional questionnaire survey.Confidential questionnaires were used to assess 2789 male and female pupils in years 7 and 9, aged 11–14 years old, from a representative sample of 28 secondary schools in East London.In total, 10.8% reported having ever tried illicit drugs and 7.3% reported ever using cannabis. Compared with white British adolescents, cannabis use in the previous month was significantly higher amongst black Caribbean adolescents. Lifetime cannabis use was significantly higher amongst black Caribbean and mixed ethnicity young people, but was lower amongst Bangladeshi, Indian and Pakistani adolescents. Living in UK for 5 years or less markedly reduced the risk of lifetime and recent cannabis use when controlled for ethnicity and social class. Glue or solvent use was reported in 3.2% of adolescents, with use significantly higher amongst Bangladeshi young people. Lifetime paan use was reported by 14.1% of the sample, and was almost completely confined to South Asian or mixed ethnicities.Ethnic differences in illicit drug use were found in the study population, and significant differences were found between ethnic groups often identified as ‘black.’ Further research is needed in understanding cultural-specific risk and protective factors in different ethnic groups, and the importance of cultural identity in mediating health risk behaviors. The high use of paan and glue/gas/solvents by Bangladeshi young people poses an unappreciated public health problem that may require targeted interventions.

Detection of recent cannabis use by saliva delta 9-THC radioimmunoassay.

A non-invasive saliva sample delta 9-THC radioimmunoassay has been applied to 352 samples from 25 male and 10 female marijuana users after administration of one-half to two standard cigarettes (27 mg delta 9-THC/cigarette) and 72 control negative subjects who ingested a large variety of foods, condiments, or medications in an attempt to demonstrate interferences. The shortest duration of a positive was 2 hrs and the longest was 5 hrs after administration of the cannabis. No positives occurred in control subjects.

Marijuana Use in Alcoholism:

Six hundred fifty patients entering treatment for drug and alcohol abuse at De Paul Hospital over a 4-month period in 1981 received a urine drug screen for cannabinoids upon admission. A random selection of 170 had 154 with alcoholism or cannabis dependency. Forty-seven (30.5%) of these had a positive urine screen of THC upon admission. Of these 47, 47 (79%) admitted recent use of marijuana when questioned during their intake interview just prior to urine screening. Only 10 (21%) denied recent cannabis use. Therefore, there was a minimal underreporting of recent cannabis use by patients entering a drug and alcohol treatment center. Also, recent cannabis use had little impact on successful initial engagement of patients into treatment. Therefore, it would appear that routine urine screening of THC in patients entering treatment is not necessary if a thorough history of drug use is obtained by competent interviewers.