One in every five medical card patients are on anti-depressant medication.
According to figures released to Newstalk under Freedom of Information legislation, almost 317,000 patients got the drugs under the scheme last year.
In 2020, over nearly 1.6 million people in Ireland were on medical cards.
Just under 20% were prescribed anti-depressant medication.
That's involves just under 317,700 people - including almost 72,000 in Dublin, and nearly 36,000 in Cork.
Other counties with high numbers last year include Galway, Limerick, Meath, Donegal, Kerry, Waterford and Wexford.
In these counties, at least 10,000 medical-card holders were prescribed anti-depressants last year.
Dr Austin O'Carroll, a GP in Dublin's inner city, says there are two main factors for the high rates.
He explained: "People who are on the medical card, by definition, have low income. We know poverty, deprivation and low income is associated with poor mental health - including higher levels of anxiety and depression.
"Secondly, we have limited access to counselling services... so often all that's available is anti-depressant medication."