Prevention interventions
We examined the available information on the effects of specific interventions that are currently provided to drug users in Europe. We ranked them as described below.
 Beneficial: Interventions for which precise measures of the effects in favour of the type of intervention were found in systematic reviews of relevant studies* evaluated with reliable methods for assessing evidence (such as GRADE**). An intervention ranked as ‘beneficial’ is suitable for most contexts.
 Likely to be beneficial: Interventions that were shown to have limited measures of effect, that are likely to be effective but for which evidence is limited, and/or those that are recommended with some caution in guidelines with reliable methods for assessing evidence (such as GRADE). An intervention ranked as ‘likely to be beneficial’ is suitable for most contexts, with some discretion.
 Tradeoff between benefits and harms: Interventions that obtained measures of effects in favour of the intervention treatment, but that showed some limitations or unintended effects which need to be assessed before providing them.
 Unknown effectiveness: Interventions for which there are not enough studies or where available studies are of low quality (with uncertain methodological rigour), making it difficult to assess if they are effective or not. Interventions for which more research should be undertaken are also grouped in this category.
 Evidence of ineffectiveness: Interventions that gave negative results if compared with a standard intervention or no intervention, for example.
^{* Study designs considered are: a) randomised controlled trials in which the unit of randomisation is an individual or a cluster (the school, community or geographical region) b) controlled trials without randomisation allocating schools, communities or geographical regions c) prospective cohort studies d) interrupted time series e)controlled beforeandafter studies.}
^{** GRADE is an approach to grading the quality of evidence and strength of recommendations. Some of the available reviews do not include measures of effect, and in these cases we therefore report the rank about evidence in the same narrative fashion as provided by the authors. In the coming year, we will produce a synthesis of the available studies with the adoption of the GRADE profiler. }
Date of last update/date of next update
The results from new systematic reviews or individual studies (provided that they are statistically powerful and valid) can change the ranking of likelihood of achieving the intended results, at any time. For that reason, we include the dates of the last update and we indicate a specific date for updating the information based of our awareness of forthcoming systematic reviews and studies.
Editorial consultation
The information compiled in the profiles by client is based on a systematic search, a selection and the assessment of existing documents. This process is systematically performed by the EMCDDA methodologists as part of a consultation process with the EMCDDA Scientific Committee members and, when considered advisable, with external experts.
The search for information
The information about guidelines, systematic reviews and studies is obtained through structured search strategies consulting:
 Pubmed (The National Library freely accessible databases);
 the Cochrane Library;
 the Cochrane Drugs and Alcohol Group’s Register of studies;
 the primary international databases for guidelines (such as: the Scottish Intercollegiate Guidelines Network; published NICE clinical guidelines; New Zealand Guidelines Group; National Guideline ClearingHouse; Guidelines International Network; La Haute Autorité de Santé; National Institute for Health and Welfare and others)
 direct consultation with the EMCDDA’s national focal points;
 information contained in national reports;
 information retrieved from the registries of ongoing studies (Current Controlled Trials; ClinicalTrials.gov);
 direct contact with leading researchers of the studies;
 International Associations websites such as:
Glossary of terms used
Below you can find definitions and further explanation for some of the terms used in this section of the Best practice portal. A more general glossary for the best practice portal is also available.
 Affectivefocused prevention intervention

A type of prevention intervention which aims to they aim to modify inner qualities (personality traits such as selfesteem and selfefficacy, and motivational aspects such as the intention to use drugs).
 BA

Beforeafter (BA) study design
 BAL

Blood alcohol level (BAL)
 Beneficial

Interventions for which precise measures of the effects in favour of the type of intervention were found in systematic reviews of relevant studies. An intervention ranked as ‘beneficial’ is suitable for most patients/contexts. See the relevant module methodology page for further information.
 CBA

Controlled beforeafter (CBA) study design. UCBA stands for Uncontrolled beforeafter study design.
 CBT

Cognitive behavioral therapy is an individual based intervention occurring in three stages. Phase 1 is aimed at determining and prioritizing the patient’s problems and constructing the treatment contract. Phase 2 is aimed at increasing coping competence and reducing risky behaviors. Phase 3 focuses on relapse prevention. Each session is administered once per week over a period of 46 months with 60 to 90minute sessions (Beck AT, Wright FW, Newman CF, Liese B. Cognitive Therapy of substance abuse. New York: Guilford Press, 1993).
 CCT

Controlled clinical trials (CCT)
 Cohort study

A cohort study is a type of observational study that follows a group of people (i.e. a cohort) over time. In a prospective cohort study, the cohort is formed and then followed over time. In a retrospective cohort study, data is gathered for a cohort that was formed sometime in the past.
 Confidence Interval (CI)

The Confidence Interval (CI) is a measure of the precision (or uncertainty) of study results. It is the interval that most likely includes the true value of the parameter we are calculating, where 'most likely' is taken by common usage to be a 95% probability. Thus the current expression of '95 % CI'. A wide CI indicates less precise estimates of effect and vice versa.
Practical interpretation
 If the RR (the relative risk) = 1, or the CI (the confidence interval) = 1, then there is no significant difference between treatment and control groups
 If the RR > 1, and the CI does not include 1, events are significantly more likely in the treatment than the control group
 If the RR < 1, and the CI does not include 1, events are significantly less likely in the treatment than the control group
 CPS

Current population survey (CPS)
 Crosssectional study

A crosssectional study is a study employing a single point of data collection for each participant or system being studied.They are usually conducted to estimate the prevalence of the outcome of interest for a given population at a given point in time.
 Evidence of ineffectiveness

Interventions that gave negative results if compared with a standard intervention or no intervention, for example. See the relevant module methodology page for further information.
Additional information for prevention
For ethical reasons this category in prevention should be considered as interventions with negative and undesired (iatrogenic) effect.  IP

Individual psychotherapy is a standard individual treatment based on counseling and motivational interviewing and focused on substance use triggers and strategies for relapse prevention. It includes elements of cognitivebehavioral therapy (CBT).
 IQR

Interquartile range (IQR)  also called the midspread or middle fifty  is a measure of statistical dispersion. It is a trimmed estimator, defined as the 25% trimmed midrange, and is the most significant basic robust measure of scale.
 ITS

Intermittent time series design (ITS)

Knowledgefocused prevention intervention

A type of prevention intervention which aims to to enhance knowledge of drugs, and drug effects, and consequences.
 Likely to be beneficial

Interventions that were shown to have limited measures of effect, that are likely to be effective but for which evidence is limited. An intervention ranked as ‘likely to be beneficial’ is suitable for most contexts/patients, with some discretion. See the relevant module methodology page for further information.
 Number Needed to Treat (NNT)

The Number Needed to Treat (NNT)indicates the number of patients that needs to be treated to obtain one respondent patient. Numerically the NNT is the reciprocal of the difference between the proportion of events in the experimental and the comparison group (absolute risk reduction). Taking into consideration that the ideal NNT would be 1 (the unreal situation in which every single patient succeeded) it is easily understood that a NNT value close to 3 or 4 would be very good.
 Adjusted Odds Ratio (AOR)

The Adjusted Odds Ratio is a way of comparing whether the probability of a certain event is the same between two groups, yet they are calculated adjusting for or controlling for other possible contributions from other variables (tipically demographic variables) in the model. An AOR equal to 1 implies that the the event is equally probable in both groups. An AOR greater than 1 implies that the event is more likely in the first group. An AOR less than 1 implies that the event is less likely in the first group.
 Odds Ratio (OR)

The Odds Ratio is a way of comparing whether the probability of a certain event is the same between two groups. Like the Relative Risk, an OR equal to 1 implies that the the event is equally probable in both groups. A OR greater than 1 implies that the event is more likely in the first group. A OR less than 1 implies that the event is less likely in the first group. In medical research, the odds ratio is commonly used for casecontrol studies, as odds, but not probabilities, are usually estimated. Relative risk is used in randomized controlled trials and cohort studies.
 p value

A pvalue is a measure of how much evidence we have against the null hypothesis. The null hypothesis represents the hypothesis of no change or no effect. The smaller the pvalue, the more evidence we have against the null hypothesis thus it is more likely that our sample result is true. Traditionally, researchers will reject a null hypothesis if the pvalue is less than 0.05.
 RBS

Responsible beverage service (RBS)
 RCT

Randomised controlled trial (RCT)
 Relative Risk (RR)

The Relative Risk (RR) is used to compare the risk in the two different groups of people, i.e. treated and control groups to see if belonging to one group or another increases or decreases the risk of developing certain outcomes. This measure of effect will tell us the number of times an outcome is more likely (RR > 1) or less likely (RR < 1) to happen in the treatment group compared with the control group.
Practical interpretation
 If the RR (the relative risk) = 1, or the CI (the confidence interval) = 1, then there is no significant difference between treatment and control groups
 If the RR > 1, and the CI does not include 1, events are significantly more likely in the treatment than the control group
 If the RR < 1, and the CI does not include 1, events are significantly less likely in the treatment than the control group
 Tradeoff between benefits and harms

Interventions that obtained measures of effects in favour of the intervention, but that showed some limitations or unintended effects that need to be assessed before providing them. See the relevant module methodology page for further information.
 Unknown effectiveness

Interventions for which there are not enough studies or where available studies are of low quality (with few patients or with uncertain methodological rigour), making it difficult to assess if they are effective or not. Interventions for which more research should be undertaken are also grouped in this category.
Additional information for prevention
For prevention interventions, this is also known as 'zero effect'.  Skillfocused prevention intervention

A type of prevention intervention which aims to enhance students’ abilities in generic skills, refusal skills and safety skills.
 Standardised Mean Difference (SMD)

The Standardised Mean Difference (SMD) is the difference in means divided by a standard deviation. Note that it is not the standard error of the difference in means (a common confusion). The standardized mean difference has the important property that its value does not depend on the measurement scale. It may be useful if there are several trials assessing the same outcome, but using different scales.
 z score (Standard Score)

The zscore (aka, a standard score) indicates how many standard deviations an element is from the mean of the population.