The over-the-counter availability of the morning after pill has been welcomed by the Irish Family Planning Association and the Irish Pharmacy Union.
The groups said it would speed up access to emergency contraception for women.
The Irish Medicines Board approved NorLevo, one of two brands of emergency contraceptive licensed in Ireland, for use as an over-the-counter medicine from today.
The drug is 95 per cent effective if taken within the first 24 hours. This drops to 85 per cent between 25 and 48 hours and 58 per cent if taken between 49 and 72 hours.
It will be available to minors as well as adults, at the discretion of the pharmacist.
Medical director of the Irish Family Planning Association, Dr Caitríona Henchion said emergency contraceptive pills offer women and girls an important second chance to prevent pregnancy when a regular method has failed, no method was used or sex was forced.
"The sooner emergency contraception is taken the more effective it is," she said.
"Access to emergency contraception directly from a pharmacy reduces delay, therefore reducing the risk of unplanned pregnancy."
The Irish Pharmacy Union also welcomed the availability of the drug.
Spokeswoman Kate Healy said they did not expect to see an increase in the number of women taking it, but they were expecting to see women accessing it earlier than before.
"The experience in other countries is that it has not lead to an increase in use or a decrease in the use of other forms of contraceptive," she said.
She also said it was up to the discretion of pharmacists to decide whether or not to dispense it to a minor. Guidelines were being produced at the moment by the Pharmacy Regulator to deal with how the drug will be dispensed, she said.
Voluntary organisation Choice Ireland said the medical board's decision would greatly increase Irish women's ability to obtain access to emergency contraception within the crucial time frame.
Spokeswoman Sinead Ahern said it was "a victory not only in the campaign to prevent crisis pregnancies but for the fundamental right of women to the tools they need to make their own reproductive choices".
