“Any medicine that’s taken has something called a half-life, which is the amount of time it takes for the concentration of the medicine in your blood to reduce by 50%,” says Deborah.
This isn’t an exact science, because different people metabolise things at different rates. How quickly you metabolise substances depends on loads of factors like your age, body size and composition, physical activity and so on. We can’t say with 100% – or even 80% – certainty when the morning after pill will have reached its ‘half-life’ in your blood because everyone is different. So what can we tell you?
“A single 30mg dose of ulipristal acetate is estimated to be around about 32 hours, plus or minus six hours,” says Deborah. “So essentially, that means that its concentration should be reduced by half within that time. That doesn’t mean it’s completely eliminated from your body, however, because then it takes another 32 hours to half it again and so on until it’s completely cleared by the body.”
So what does this mean? One thing to note is that the morning after pill is only effective for a single episode of unprotected sex. It is designed to be used in an emergency, after contraceptive failure or unprotected sex. The morning after pill will not continue to protect you from pregnancy if you take it and then have unprotected sex again. As a side note, the morning after pill is intended for emergency use only and not intended as a regular contraceptive option.
“No one person is the same,” says Deborah. “We don’t all fit into one neat box when it comes to our metabolism and how quickly we clear medicine. Having more fat or compromised kidney or liver function that affects the metabolism of drugs would all have an impact.”