The dosage of the morning after pill is to be changed to try to reduce the number of unwanted pregnancies.
Levonelle is controversial
The Department of Health has announced that Levonelle will now be given as two pills taken together - rather than 12 hours apart.
It is hoped this will cut pregnancies caused by women forgetting to take the second dose.
The drug is available over-the-counter and on prescription.
The emergency contraceptive is highly controversial.
Opponents say it encourages a reckless attitude to sex, with women relying on it instead of more conventional forms of contraception.
There has also been vociferous opposition to moves to make it available to schoolgirls to try to cut teenage pregnancies.
The single dose has been introduced following large-scale study by the World Health Organisation which found it was safe and effective.
New packs - which have been approved by the Committee on Safety of Medicines - will be made available to patients before the end of the year.
Health Minister Lord Warner said: "The evidence shows that the new dose is
safe and effective.
"There are clear benefits to patients in making this change - a single dose
will improve compliance and hence reduce the number of unwanted pregnancies."
Levonelle, and a prescription-only form known as Levonelle-2, were originally both licensed as two 0.75mg tablets taken 12 hours apart.
The WHO trial, which included more than 2,700 women, compared this way of using the drug with a single 1.5mg dose.