The cost comes as an estimated 171,615 more people in NSW reported mental health issues consistent with depression and anxiety in 2021 that were linked to lockdowns.
In 2021, NSW entered a lockdown amid the spread of the Delta variant, with restrictions continuing for nearly four months in Sydney.
The findings are detailed in the first chapter of Aftershock: Addressing the Economic and Social Costs of the Pandemic and Natural Disasters, a research series commissioned by the NSW Council of Social Service (NCOSS) and published on Thursday.
The report found evidence of growing emotional distress in recent years, including a 46 per cent increase in 12- to 17-year-old girls arriving at emergency departments for self-harm or suicidal thoughts between 2018 and 2021.
There was also a 9.3 per cent increase in prescriptions for depression medication during the same period, which is more than double the rate of other medicines.
NCOSS chief executive Joanna Quilty said the estimated direct cost to the Australian economy of poor mental health had been about $40 billion to $70 billion a year before COVID-19.
"We know that people's mental health worsened as a result of extended lockdowns across our state and that it was women with young children who were most affected," Ms Quilty said.
"On top of that, natural disasters have since added to the picture of rising psychological distress across communities in NSW."
She said the cost to the NSW economy of $7.4 billion over five years was a low estimate.
"This is conservative, with the modelling looking only at the impacts of COVID lockdowns on NSW's working population," Ms Quilty said.
"It doesn't take into account natural disasters or mental health impacts for the whole community."
Mental Health Co-ordinating Council CEO Carmel Tebbutt said the research showed the psychological effects of recent disasters had hit children, women and dependent elderly people particularly hard.
"Community mental health services are vital in responding to disasters as they reduce the burden of mental illness by supporting recovery and minimising the severity and long-term risks," she said.
Ms Tebbutt welcomed the NSW government's June budget commitment of $2.9 billion to mental health services over 2022/23, but said the state continued to lag behind others on residential and community mental health services.
It comes after the latest national figures show 56 COVID-19-related deaths were reported on Wednesday, along with 15,732 new cases, 3199 people in hospital, with 93 in intensive care units.
LATEST 24-HOUR COVID-19 DATA:
NSW: 5790 cases, 29 deaths, 1836 in hospital with 37 in ICU
Tasmania: 244 cases, one death, 42 in hospital with two in ICU
SA: 749 cases, one death, (hospital data unavailable).
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