Morning-after pill made free at pharmacies in Wales
Emergency contraception can now be obtained without charge from pharmacies across Wales, while still costing about £25 in the rest of the UK.
Community pharmacists in Wales can also give the "morning-after pill" to under-16s, if clinically appropriate - a move that has angered campaigners.
Some GPs have warned about "missed opportunities" to educate young women about sexually transmitted diseases.
Ministers said chemists had a vital role in reducing unwanted pregnancies.
Parts of Wales have some of the highest teenage pregnancy rates in the UK.
Health minister Edwina Hart announced the move last November, saying she wanted professional advice available without appointment and "easily accessible within the 72-hour time span necessary for emergency contraception to be most effective".
The morning-after pill is free to women across the UK if it is prescribed by a GP or family planning clinic, but Wales is the first nation to offer emergency contraception without charge on the high street.
End Quote Josephine Quintavalle Comment on Reproductive Ethics
The idea that young girls can just walk into a chemist will mean they become even less responsible about sexuality”
The change will affect 700 pharmacies.
The pill will be allowed to be dispensed to under-16s if pharmacists decide if it is clinically appropriate to dispense it and if the girl requesting the pill understands what she is asking for.
But Josephine Quintavalle, founder of Comment on Reproductive Ethics (Core), said it would encourage "irresponsible" attitudes to sex.
She told BBC Wales: "It's absolutely the wrong way to address the problems of high rates of teenage pregnancy in Wales. The idea that young girls can just walk into a chemist will mean they become even less responsible about sexuality.'Know the dangers'
"I don't see how any chemist can stop a 12-year-old taking the morning-after pill, some 12-year-olds do look like 16-year-olds these days."
Dr Marina Arulanandam, of the Llandaff Surgery in Cardiff, said GPs and family planning clinics had a vital role to play in educating women about a whole range of issues like sexual health, ectopic pregnancies and possible side-effects of taking the medication.
She said: "It's important young people know the dangers of unprotected intercourse.
"It's not just pregnancy they should worry about, it's STDs [sexually transmitted diseases] - these are huge problems we need to be addressing and I don't think the pharmacies will have enough time to do this."
End Quote Janet Pearce Marie Stopes International
This is an important step forward in preventing unplanned pregnancies and abortions amongst women in Wales”
Practice nurse Louise Lidbury said she was concerned no universal guidance had been handed out to chemists.
"They should be asking how many times they have used (the pill), things like consent if it's a young girl and looking at their past medical history.
"They can go to one chemist and then another and there's no audit trail if they travel from chemist to chemist.
"I've had a young girl aged 14 in a relationship with a 19-year-old and she did end up discussing it was not entirely consensual and that was an opportunity for me to discuss with her how she was going to manage that situation.
"That opportunity could have been lost if she was going to get an over-the-counter morning-after pill."
However, the move has been welcomed by family planning charity Marie Stopes International.
Janet Pearce, a nurse adviser at the charity's call centre, said: "This is an important step forward in preventing unplanned pregnancies and abortions amongst women in Wales.
"It will be particularly beneficial for low income women and young women who may risk a pregnancy because of the cost associated with the emergency contraceptive pill."
She added that women often experienced delays when trying to get emergency contraception via their GP or a family planning clinic.
Ian Cowan, chairman of Community Pharmacy Wales, said the service as it already exists made a "massive difference to women's lives" and was "immensely reassuring to the women who need it".