A quarter of people who use moneylenders run into problems paying back the loan, research has shown.
A Central Bank report found about 360,000 people are using the businesses at present and outstanding loans are worth about 200 million euro.
And it found that 13% of people surveyed are aware of illegal moneylenders operating in their area.
The report said that the amount of people in difficulty meeting payments has jumped from 9% in 2007 to 25% earlier this year.
It revealed that the most frequent loan term offered is about nine months and at a rate of 125%, but rates can vary from 17.23% to 188.45%, and soar from 37.79% to 287.72% if a collection charge is included.
The vast majority of borrowers in difficulty cited a drop in household income as the main reason for struggling with repayments and almost half blamed changes in their work or benefits.
One-fifth said it was because their personal circumstances had changed and others said they had been hit with household expenses and an unexpected bill.
The Central Bank's director of consumer protection Bernard Sheridan urged people in difficulties with loans to go to the Money Advice and Budgeting Service (Mabs).
"Loans from moneylenders can be very expensive, especially when used on an ongoing basis," he said.
"While there are some positive findings in relation to how licensed moneylenders are treating their customers and also in the increasing level of awareness of the costs of such loans, the Central Bank will continue to monitor this sector closely and take action where necessary to protect borrowers' interests."
The information was based on surveys of 40 licensed moneylenders and 500 customers who had paid their loans off while in-depth research was conducted with a smaller number of lenders, customers and stakeholders.
It said 62% of those surveyed were women, while the rest were men.
Of these, the most likely customer for a moneylender was a married mother-of-two in her late 30s or early 40s.
The Central Bank said the most common users of moneylenders are aged 35-54 and are more likely to be in the lower socio-economic group.
Pay-day moneylending is not allowed in Ireland.
The Central Bank said it regards a moneylender as anyone who offers credit by way of a cash loan or goods on credit or a catalogue sale.
There are 43 moneylenders in Ireland, with 40 actively engaged in the business. Repayments can be made by direct debit, front door collections or long-term repayment to retailers or catalogues.
Some 80% of moneylenders are door-to-door operations.
Here are some other statistics on people who use moneylenders:
:: The number who own their own home, either outright or owe a mortgage, has increased to 53% - up from 41%.
:: One-quarter live in local authority rented housing and 7% live with either parents or relatives.
:: Customers are likely to initially become aware of their moneylender through referrals from friends and family.
:: The most common loan amount is 200-500 euro.
:: The most common reasons for borrowing have remained unchanged over the last six years - primarily for personal items such as goods or clothes and family-related occasions.
:: Convenience and ease of access to credit is the main catalyst for using moneylenders.
:: More than one in five customers have loan arrangements with more than one moneylender.
:: Almost eight in 10 customers said that they understood the cost per 100 euro borrowed of their most recent loan.