Trente-cinq pour cent à 45 % des patients psychotiques consomment régulièrement du cannabis, avec des effets néfastes sur la rémission des symptômes positifs, le niveau de fonctionnement et le risque de rechute. Des approches motivationnelles ont été développées pour les doubles diagnostiques afin de s’accommoder aux consommateurs de substances souffrant de psychose. La banalisation du cannabis comme une drogue « douce » jugée inoffensive, la fréquence de sa consommation chez les jeunes et son appétence et sa nocivité particulière pour les personnes souffrant de psychose implique de développer des approches spécifiques à cette population. Notre objectif est de développer une approche pragmatique, sans jugement, inspirée du modèle d’intervention motivationnelle adapté aux doubles diagnostics afin de viser une réduction des risques liés à cette consommation. Cette adaptation est basée sur une revue de littérature des interventions motivationnelles pour les doubles diagnostics, sur notre expérience du modèle motivationnel avec des patients souffrant de psychose et inspiré initialement par les interventions brèves à l’intention des consommateurs d’alcool à risque. Les principes d’une intervention motivationnelle adaptée aux patients psychotiques consommateurs de cannabis sont : (a) l’abord simultané des questions liées à la psychose et au cannabis et de leur interaction ; (b) la prise en compte des troubles cognitifs liés à la maladie et au traitement ; (c) l’adaptation des techniques d’écoute réflexive ; (d) la structuration des entretiens, notamment à l’aide de la grille de balance décisionnelle (GBD). Les quatres premières séances comportent : (1) la création d’une alliance et évaluation de la consommation de substance ; (2) le développement de la motivation au changement en augmentant les contradictions dans le discours du patient ; (3) la définition des objectifs en fonction du stade de motivation au changement et  ; (4) à partir de la quatrième séance, adaptation de l’intervention au stade de motivation au changement. Dans une telle approche, le premier pas est du côté du thérapeute, qui manifeste de l’empathie et cherche à comprendre les raisons de la consommation. Contrairement à une approche classique qui viserait essentiellement à souligner les dangers du cannabis et à interdire sa consommation, le patient dévoile les aspects ambivalents de sa consommation avec un minimum de réactance et prend conscience des liens entre les troubles et la consommation. Cette méthode est particulièrement adaptée aux patients ambulatoires en précontemplation, c’est-à-dire sans perception du problème, ni désir de changement.

People suffering from psychiatric disorders abuse alcohol or illicit substances twice as frequently as the general population. This problem is even more frequent in the early phase of psychotic disorders where prevalence of substance abuse ranges, according to various studies, from 35 to 65% during first psychotic episode. Cannabis is currently the most frequently used substance, and although its impact is often minimised, many data suggest it constitutes a risk for psychosis at three levels: (a) possible toxic psychosis in healthy individuals, (b) relapse of positive symptoms in schizophrenia and (c) raises the risk of schizophrenia when used early during adolescence. Despite a persistent controversy regarding some of these findings, they have constituted a sufficient body of evidence to support the development of specific interventions for psychotic patients. Various authors have described the fundamental elements of such dual diagnosis treatments, and some intervention programs have recently been developed. However, their relative complexity and the long duration of such interventions are often not well adapted to patients with limited motivation and low level of insight. Moreover, many obstacles arise that complicate their application to early psychotic disorders: minimisation of deleterious effect of cannabis by young people, distrust linked to psychotic symptoms, cognitive disturbances, stigmatisation of psychiatry, and use of cannabis as a means to socialise with peers. It is therefore important to adapt interventions to the specific needs of such patients and particularly to adopt a realistic attitude, aiming at increasing motivation to change habits and minimising associated risks rather than total abstinence. Our objective is to develop a pragmatic, non-judgemental approach, based on motivational interviewing techniques that is adapted to early psychosis with comorbid cannabis abuse, aimed at reducing the risks associated with abuse. In this article, we describe the basic principles and various stages of a brief motivational intervention developed for the treatment of cannabis abusers, going through the early phase of a psychotic disorder. The conceptualisation of the intervention was based on an extensive literature review and our experience in the treatment of such patients, as well as in the treatment of alcohol abuse through motivational interview.

Our intervention uses motivational interviewing techniques (empathic, non-judgemental approach, aimed at developing insight regarding potential consequences of cannabis abuse through the exploration of both its positive and negative aspects) and can be adapted to the patient's stage of motivation for change. Its basic principles are: (a) to address questions related to psychosis and cannabis simultaneously; (b) to take into account cognitive dysfunction related to illness and treatment; (c) to adapt techniques of reflective listening; and (d) to structure the interview through frequent summaries and by considering successively the positive and negative aspects of cannabis. The intervention is composed of four sessions: (1) creation of an alliance and evaluation of the level of cannabis abuse; (2) development of motivation to change by increasing contradictions between patient's affirmations; (3) definition of objectives according to the level of motivation to change; and (4) adaptation of the subsequent intervention according to the degree of motivation to change.

A pilot study showed that this intervention can be implemented in the target population. It revealed that it facilitated the establishment of a trustful relationship, in the frame of which ambivalence regarding cannabis abuse could be explored. The fact that the therapist makes the first step, shows empathy and tries to understand patient's motivations to use cannabis, leads patients to expose their ambivalence with less reluctance and to become more aware of the possible links between cannabis and psychotic disorders.

This method is particularly well adapted to patients who are in a pre-contemplative stage. Additional studies are needed in order to evaluate its efficacy in terms of decrease in the risks related to cannabis abuse.