However scientists writing in the journal Obstetrics and Gynecology claim it may be reasonable to take the morning-after pill in other circumstances too. For instance, if you weren't in a relationship and not having sex frequently - which means you may not be taking the pill or any other form of regular contraception - you could take the morning-after pill just before or after having sex.
In fact, according to the researchers, some women in Africa and Asia use the morning-after pill as a planned method of birth control, rather than an emergency backup.
But is it safe to do so? The researchers say it may well be, despite the fact that the morning-after pill is not promoted as a regular form of contraception.
Their report is based on a review of studies on levonorgestrel, the synthetic hormone used in many brands of morning-after pills, which works by stopping you ovulate. They found women who used the morning-after pill at the time of having sex had an estimated 5 chance.
However the morning-after pill wasn't as effective as long-term contraception methods such as the regular pill or the contraceptive patch, the researchers add.
There again, given the cost of the morning-after pill (around £25 a pop in most pharmacies), it's an expensive option, even when you only use it occasionally.
Or is it? What do you think?