Intramuscular injection (IMI) is the process of administering a drug treatment into muscle tissue. The transmission of skills in this care practice is essentially based on the experience of peers. In France, there are no official guidelines for this technical procedure.

Haloperidol decanoate is widely used in psychiatry. This long-acting antipsychotic treatment considerably reduces the risk of relapse and hospitalization. It is administered by IMI. This treatment is invasive, painful and risks complications for the patient. Nurses must ensure that the treatment is as painless as possible, and adapt their practice in line with current recommendations.

Among the various IMI techniques available, the "Z-track" and the "Airlock" limit leakage into subcutaneous tissues when the needle is withdrawn, by locking the active product into the muscular tissues. According to an exploratory study (n=303), 73% of nurses observe active product leakage after injections, and 89% of nurses are not familiar with either the "Z-track" or "Airlock" techniques.

Many foreign studies have been carried out to demonstrate the relevance of these techniques, particularly in terms of pain reduction during treatment, but the results have yet to be confirmed.

The investigators hypothesize that the combined use of the "Z-track" and "Airlock" techniques during intramuscular injection of Haloperidol decanoate is more effective in reducing patient pain than usual practice.

This is a multicenter, prospective, randomized, double-blind, controlled, study in 2 parallel groups.

Experimental and control administration protocols will be standardized to harmonize injection practices between the different nurses providing care, and to control some variables. Nurses will have been trained in these protocols and in experimental injection techniques.

The experimental group will be offered an intramuscular injection using the "Z-track" and "Airlock" techniques, while the control group will have an "usual" injection.

An intermediate analysis of futility and efficacy is planned once 50% of the planned sample has completed the study.

The object of the research is the intramuscular injection procedure - Product injected: haloperidol decanoate (Haldol Decanoas®).

Inclusion Criteria:

• Adult ;
• having an outpatient treatment in a Mental Health Community Center ("Centre Médico-Psychologique" CMP in french) ;
• with an CIM-10 diagnosis between F20-F29 (Schizophrenia, schizotypal disorder and delusional disorders);
• communicative and able to give free and informed consent to the study;
• prescribed Haloperidol decanoate;
• covered by the french social security

Exclusion Criteria:

• Minor ;
• pregnant women ;
• with insufficient understanding of the French language to understand the VAS;
• suffering from any of the following known somatic comorbidity : coagulation disorder, leucopenia, immunosuppression;
• currently prescribed treatment: immunosuppressant, anticoagulant, antibiotic, antiretroviral, other products administered by IMI at dorsogluteal injection sites (antibiotic therapy, hormone therapy, vitamin therapy).

Advanced practice nurses (APNs) will carry out clinical examinations before and after the treatment. They will not be present during the treatment, and the patient will not know the technique used, in order to ensure a double-blind evaluation. Only the nurses performing the injection will be aware of the technique used (experimental or control).