One in five young women used the morning-after pill last year, causing experts to warn them that they are putting their health at risk.
And a quarter of a million women have used the drug three times or more.
The figures are based on a poll of 3,000 people by The Co-operative Pharmacy on sexual behaviour trends over the past twelve months.
The morning-after pill contains a powerful dose of hormones, which can act to abort an embryo.
The survey also revealed that chlamydia is the most common sexually transmitted disease, followed by genital herpes and gonorrhoea.
A sixth of women who took part in the survey admitted having had a sexually transmitted infection.
And according to the Health Protection Agency, almost half a million new infection cases are diagnosed in the UK each year.
The survey has caused concern to Mandeep Mudhar, Head of NHS development at The Co-operative Pharmacy.
“Our research shows that some women are taking unnecessary risks with their health”, he said.
He added: “The emergency contraceptive pill does not protect against sexually transmitted infections”.
The statistics come after warnings last year from family values groups about the dangers of the morning-after pill.
Norman Wells, of campaign group Family Education Trust, said: “The easy availability of the morning-after pill has a damaging social effect, by lulling young people in particular into a false sense of security, encouraging a more casual attitude to sex, and exposing them to increased risk of sexually transmitted infections.”
And Josephine Quintavalle of Pro-Life Alliance said: “This is not a contraceptive, it is an abortive agent.”