Depression remains the most common psychiatric illness in the country, according to figures published today by the Health Research Board.
The board said depression accounted for 27% of all admissions to psychiatric units and hospitals last year, followed by schizophrenia (20%), mania (15%) and alcoholic disorders (14%).
It also said depression was the only mental illness that was not decreasing at present.
Spokesman Dr Dermot Walsh said the figures indicated that existing treatments for the condition were not working.
"The treatments available. The anti-depressant drugs, for example, don't seem to be that effective, either in preventing it or cutting it short when it occurs in the first place," he said.
"Of course, that's mirrored to some extent by the increase we've had over the past 20 years in suicide rates."