Usually emergency pill is a safe drug but excessive and frequent use isn't recommanded because it contains high doses of hormone and may cause nausea, vomiting, headache and menstrual irregularities. I mean, though it's used for protection against pregnancy, it disturbs your hormonal balance, you may have irregular periods. This is an emergency contraceptive pill and not a family planning pill. Taking this regularly will cause irreparable damages. If you take for a longterm side effects like weight gain, irregular periods,depression & vomiting may be seen. So better do safe in future to avoid its use and side effects.