Irish researchers from St Patrick’s Mental Health Services and University College Cork are among those leading in a major international study on clozapine usage for the treatment of treatment-resistant schizophrenia.
The global study is the largest ever assessment of clozapine usage and included data from 75 countries gathered over a period of ten years from 2014 to 2024. As a result of this research, estimates of national clozapine usage are now available in many countries for the first time, including Ireland, where it was estimated that less than 50% of those with treatment-resistant schizophrenia are being prescribed clozapine.
Treatment-resistant schizophrenia and clozapine
Schizophrenia resistant to typical antipsychotics, also known as treatment-resistant schizophrenia, impacts 30–40% of people diagnosed. International guidelines in psychiatry suggest that the antipsychotic medication clozapine is the most effective treatment in managing schizophrenia unresponsive to other antipsychotics.
However, prior research from 2014 has shown that clozapine is chronically under-prescribed globally and this new study aimed to explore if international trends of clozapine prescribing have improved since this time.
A global study across 75 countries
Researchers from St Patrick’s Mental Health Services and University College Cork, as well as researchers from the UK, New Zealand, Australia, the US and across Europe, obtained national estimates of clozapine usage from 75 countries through an analysis of national prescribing databases and global pharmaceutical sales data.
The study found that in 2024, substantial variation in international use of clozapine remains. While global clozapine usage has increased, this is not uniformly. Although 60% of countries demonstrated an increase in clozapine use, increases were modest.
New Zealand was the country identified as having the highest sustained rates of clozapine use over the study period, followed by Finland. Out of the 75 countries assessed, only New Zealand and Finland achieved rates of clozapine prescribing similar to the population proportion with treatment-resistant schizophrenia.
Commenting on the study
Dr Ita Fitzgerald, lead researcher on the study and Advanced Specialist Pharmacist with St Patrick’s Mental Health Services, said:
“Pharmacy research plays a critical role in advancing mental healthcare by identifying gaps between available treatments and the real-world needs of service users. It is hoped that this research is the first step in helping to shape future prescribing practice and improving much needed, timely service user access to clozapine.”
Dr Mikkel Højlund, associate professor of psychiatry and psychopharmacology from the University of Southern Denmark said:
“Comparing clozapine use across the world is very important because, despite decades of evidence that clozapine can transform outcomes for people with treatment-resistant schizophrenia, access to this treatment still appears to be underutilised. By mapping clozapine use globally and relating it to health-system features such as access to psychiatrists and monitoring policies, we sought to identify structural barriers which might need more attention to support better access to an essential treatment.”
Next steps in clozapine research
The research team involved in this study have identified the next steps for clozapine research as identifying how to effectively increase rates of clozapine prescribing. This will include studying systems of clozapine management in countries that have sustained high rates of clozapine prescribing.
Publication and related research
The findings of this study have been published in The Lancet Regional Health – Europe.
Other recent research from the Pharmacy Department in St Patrick’s Mental Health Services include:
- From Idealist to Realist – Designing and Implementing Shared Decision-Making Interventions in the Choice of Antipsychotic Prescription in People Living with Psychosis (SHAPE): Part one and part two
- Informing the development of antipsychotic-induced weight gain management guidance: patient experiences and preferences – qualitative descriptive study, available here.
Media queries
If you have press queries, please contact our Communications team below.
