There are 40 beds in the unit, but only 37 are currently funded.

Mental Health Minister Shane Rattenbury said with the unit having been "under pressure from some time now", $1.7 million would be made available in the upcoming ACT budget to recruit staff to treat patients in the remaining three beds in 2019-20. Over the next four financial years, the figure is set to rise to $7 million.

Funding for the additional beds is one of eight mental health initiatives included in the budget.

Mr Rattenbury said one-third of Canberrans would need mental health care at some stage in their lives and increasing numbers of people were accessing treatment, because of an increasing population and decreasing stigma.

"There is a significant community discussion going on about mental health. There is a strong message that says, 'You should speak out and seek help'," Mr Rattenbury said.

"There is still stigma around mental health, but people are taking that message and they are coming forward and seeking support.

"That's really positive, but it creates new pressures for government and we need to make sure the service responds to that changing community expectation."

In response, Mr Rattenbury has announced $6 million in mental health funding for 2019-20. The planned outlay over the next four fiscal years is $24.2 million.

One initiative will see Canberra Hospital's adult mental health unit receive a dedicated electroconvulsive therapy service.

This type of treatment, once known as electroshock therapy, was famously depicted in the film One Flew Over the Cuckoo's Nest, and has since carried negative connotations. Attitudes towards it have shifted significantly in recent times and ACT chief psychiatrist Dr Denise Riordan said representations in movies and the media were "quite significantly removed" from how it was performed in contemporary health services.

Dr Riordan said the treatment, which electrically induced seizures in patients under anaesthetic, was very effective for serious mental illnesses including severe depression and mania.

It was generally used when patients had not responded to other methods, but at present, access to the therapy in the ACT was limited because there was only a dedicated service for public patients at Calvary Hospital.

"What that has meant is that people have to wait and the suffering that they're enduring goes on for longer," Dr Riordan said.

"It's also meant that because we haven't been able to deliver it reliably from the Canberra Hospital site, people have to go from the adult mental health unit to Calvary Hospital and back, so there's obviously a lot of transport involved and that's an added burden and stress to people.

"We're quite pleased with this announcement and what we're hoping is we can actually provide a more reliable, robust and timely treatment that we know is effective to people here in the ACT."

Dr Riordan said the $1.8 million set aside for the service in 2019-20 would be used to fund the necessary infrastructure. The service was set to receive $5.1 million over four years.

Mr Rattenbury said modern research on electroconvulsive therapy was very clear on its effectiveness, and ACT Health staff had strongly supported the establishment of a service to deliver it at Canberra Hospital.

"What I think this will do is open up a new channel of treatment for some people," he said.

The Calvary Hospital service currently performs about three sessions of electroconvulsive therapy per week, but the new Canberra Hospital service will allow the ACT to meet the demand of three sessions every weekday for 50 weeks a year.

The budget package also includes $179,000 to establish an eating disorders specialist clinical hub and a community-based intervention support service next financial year. Over four years, that is set to rise to $2.2 million.

Two carer engagement clinicians will be hired to pilot a range of activities to better support carers for people with mental health conditions. The $457,000 for that initiative will be split almost evenly over the next two financial years.

A new police, ambulance and clinician early response service will be planned and designed in 2019-20 at a cost of $323,000.

The mental health consultation liaison service is also set for an expansion, allowing it to run seven days a week, with $4.6 million on the table over four years. Of that, $800,000 will be spent next financial year.

The justice system is also a focus of budget funding. Specialist nursing staff will be recruited to deliver drug and alcohol treatment services for Alexander Maconochie Centre detainees seven days a week, up from five days, at a cost of $258,000 in 2019-20 and $1.1 million over four years.

The final initiative is hiring new staff to work with mental health patients who appear before the ACT courts, at a cost of $731,000 next financial year. Over four years, that rises to $3 million.