Answers to Frequently Asked Questions About...
Effectiveness
If I am using enzyme inducers (such as Dilantin, the antibiotics rifampicin or griseofulvin, or St. John's Wort), will it make emergency contraceptive pills less effective? Are the instructions for using the pills different?
Medications and herbal supplements that may make
regular birth control pills less effective may also reduce the effectiveness
of emergency contraceptive pills. This applies to both progestin-only pills, (like Plan B One-Step, Next Choice One Dose, Next Choice and Levonorgestrel Tablets), and ulipristal acetate (ella). So if you are using an enzyme inducer
(such as Dilantin, the antibiotics rifampicin or griseofulvin, or
St. John’s Wort), it probably makes sense to increase the dose
of emergency contraceptive
pills (also known as "morning
after pills" or "day after pills").
The Faculty of Family Planning
and Reproductive Health Care Clinical Effectiveness Unit there advises
patients taking liver enzyme inducers who are also using progestin-only
emergency contraceptives (like Plan B One-Step, Next Choice One Dose, Next Choice and Levonorgestrel Tablets) to take 3 mg levonorgestrel. This would be two Plan B One-Step or Next Choice One Dose tablets or four Next Choice or Levonorgestrel Tablets tablets, at
one time. Read more here.
If you are using “combined”
birth control pills for emergency contraception (which contain
progestin and estrogen, such as regular birth control pills used as EC), you should double the first dose of hormones
you take (for more information about the standard doses and instructions
for emergency contraceptive pills, click
here). Alternatively, some health care providers suggest that you increase
the number of pills in each dose by 50%, meaning that you take one
and half doses each time (for more information on specific dosages
birth control pills used for emergency contraception,
click here).
As of yet, there are no guidelines for how to adjust ulipristal acetate (ella) intake if you're using enzyme inducers.
In general, if you increase your dose of emergency
contraceptive pills, you are more likely to feel sick to your
stomach, which is already one of the common side
effects. To avoid that, you can try taking 25-50 mg of the anti-nausea
medication meclizine (sold as a generic drug or under the brand names
Dramamine II or Bonine in the United States) one hour before taking
the first dose of emergency contraception.
A thorough and up-to-date academic review of the medical and social
science literature on emergency contraception is available; click
here for the
PDF.