Smokers will not be able to buy packs of 10 cigarettes in Ireland after Thursday.
A delayed ban on 10-packs comes into force, coinciding with international No Tobacco Day on May 31.
The Department of Health has signalled for years that 10-packs would be forbidden, largely because they are a magnet for under-age smokers.
The ban was originally scheduled for last autumn, but the tobacco industry lobbied for a delay on the grounds that they had big stocks of 10packs which would have to be sold before the deadline.
The ban is also timely because a conference on the problem of children smoking is also being held on Thursday in Dublin's Croke Park conference centre.
Dr Fenton Howell, Director of Public Health for the Health Service Executive in Dublin North-East will chair the conference. It will examine why children start to smoke, and look at measures to reduce youth smoking. Dr Howell is a former chairman of Action on Smoking and Health (ASH).
'Lolly cigarettes', confectionery resembling tobacco products, is also banned from Thursday.
Fines up to €3,000 or imprisonment for up to three months are the initial penalties for retailers.
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