Background: People with 22q11.2 deletion syndrome (DS) are assumed to be especially vulnerable to developing mental illness such as psychosis. Aim: The study was established to contribute to knowledge about metyrosine medication in patients with 22q11.2 DS and psychosis. Methods: A case study was established including a woman with intellectual disability, 22q11.2 DS, and psychosis. Metyrosine medication was implemented, as conventional anti-psychotic medication was unsuccessful. Results: Effect of metyrosine medication included both psychotic symptom relief with decreased aggressive behaviour. Adjunctive milieu therapy contributed to compliance. Conclusion: For patients with 22q11.2 DS and psychosis, metyrosine medication may prove effective. However, there are significant ethical dilemmas related to metyrosine medication for psychotic symptoms.