Irish Researchers Among Those Leading in Largest Ever International Study on Clozapine Usage for the Treatment of Schizophrenia
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 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 10 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.
Schizophrenia resistant to typical antipsychotics (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 has improved since this time.
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.
Speaking about 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.”
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.
The findings of this study have been published in The Lancet Regional Health – Europe. You can access the study here.
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.
For further information contact:
Katie Crosby, Communications Officer, St Patrick’s Mental Health Services
Phone: 01 249 3396/086 862 3298 Email: kcrosby@stpatricks.ie
A map representing global rates of clozapine utilisation in 2024 is presented below:
Global utilisation of clozapine in 2024. Utilisation rates are expressed in defined daily doses (DDD)/1,000 inhabitants/day. NA = No data.
St Patrick’s Mental Health Services (SPMHS) is Ireland’s largest independent mental health service provider. It provides outpatient care through its Dean Clinics and day patient services through its Wellness & Recovery Centre. A multidisciplinary inpatient service is provided through its three approved centres: St Patrick’s University Hospital (208 beds), St Patrick's, Lucan (52 beds) and Willow Grove Adolescent Unit (14 beds). SPMHS also offers homecare services and remote access to its services through phone or video call.
The organisation’s mental health services cater for addictions and dual diagnosis, anxiety disorders, bipolar disorder, depression, eating disorders, psychosis and mental health difficulties in older adults as well as young adults.
SPMHS’ vision is to see a society where everyone is empowered and given the opportunity to live mentally healthy lives. St Patrick’s Mental Health Services strives to provide the highest quality mental healthcare and works to promote positive mental health; to raise awareness about mental health; and to advocate for the rights of those experiencing mental health difficulties. This is achieved through a human rights-based approach, through the enhancement of evidence-based knowledge and by striving to be at the forefront of new initiatives and advances in the field.
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