The successful implementation of a 10-year mental health strategy for Northern Ireland is at risk without sustained investment, an Audit Office report has said.
Comptroller and Auditor General Dorinnia Carville's report said mental health problems in the region are approximately 25% higher than in England.
She also said one in five adults in Northern Ireland show signs of mental health problems, with an estimated one in eight young people experiencing anxiety and depression.
Ms Carville said the financial impact to Northern Ireland of mental health treatment and lost productivity is "conservatively estimated at £3.4 billion annually."
The report provides an overview, considering issues around mental health strategy, funding, activity and data.
It said the higher prevalence of mental health problems in Northern Ireland has been linked with both greater levels of deprivation and with the impact of the Troubles.
The report said that in 2022-23, a total of £345 million has been allocated for mental health services, representing 5.7% of the overall health and social care budget.
But it added that despite higher prevalence levels, funding for mental health in Northern Ireland is lower than elsewhere in the United Kingdom and Ireland.
The report estimated that bringing funding levels into line with elsewhere in the United Kingdom would require additional funding, which could be as much as £190 million annually.
The report welcomed the publication of the overarching Mental Health Strategy 2021-31, launched by the Department of Health in June 2021.
The total cost of the strategy's reforms of mental health services are estimated at £1.2 billion over the 10 years to 2031.
However, the report noted that funding for these reforms is not available from within existing departmental resources and will require additional funds to be secured through an Executive.
Northern Ireland is currently without a functioning Assembly and Executive.
The report said the absence of additional, secured funding has meant that progress on delivering the 10-year strategy has been limited.
Ms Carville stated: "The costs of mental ill-health are significant in Northern Ireland.
"As well as the human cost, the financial impact to society as a result of care, treatment and lost productivity is conservatively estimated at £3.4 billion annually in Northern Ireland.
"There are, therefore, significant benefits to be derived from improving mental health here.
"The Strategy for Mental Health 2021-31 provides a direction of travel for achieving the reform and improvement of services that is needed.
"However, adequate and sustained funding will be necessary to realise the strategy's vision."
The report also considered the impact of Covid-19 on services.
It said while services were maintained throughout the pandemic, a combination of changes in people's health-seeking behaviour, and reductions in the availability of some services, saw the number of referrals reduce.
In 2021-22, referrals were approximately one fifth below pre-pandemic levels.
Despite reduced levels of referrals, mental health waiting lists have continued to grow.
The report said that in March 2022 around 16,000 patients were on a waiting list for mental health services, almost 20% higher than pre-pandemic.
It also said that performance against waiting list targets has deteriorated.
Around half of those on mental health waiting lists wait longer than the nine and 13-week target standards, with particular issues identified in relation to psychological therapies.
Workforce issues are identified in the audit report as a key barrier to access and performance against waiting time standards.
It also drew attention to data limitations in mental health in Northern Ireland.
The report recommended improvements to how outcomes are measured, in order to "better evaluate the effectiveness of services in improving people's mental health, and to determine whether services represent value for money."
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