Can you take Plan B while on medication?
Taking this emergency contraceptive causes a boost in the body’s hormone levels, which increases the likelihood of preventing pregnancy. However, there are medications and herbal supplements that could affect the way the Plan B pill works. Medications that may make Plan B less effective include: barbiturates.
Do any pills interfere with Plan B?
Some drugs or herbal products that may decrease the effectiveness of progestin-only pills include: barbiturates (including primidone) bosentan. carbamazepine.
Is Plan B affected by amoxicillin?

No interactions were found between amoxicillin and Plan B One-Step. However, this does not necessarily mean no interactions exist. Always consult your healthcare provider.
What cancels out a Plan B?
If you take it right after sex, it can prevent you from ovulating if you haven’t started already (1). If you have sex at the time you ovulate or after you ovulate, your emergency contraception pill won’t be effective (7).
What can make Plan B not work?
Plan B is 95% effective if you take it within 24 hours and 89% effective within 72 hours. But it might be less effective if you are ovulating, or have unprotected sex after taking Plan B. It is also less effective for women over 155 pounds — if this is the case, try a pill like Ella.

How do you know Plan B didn’t work?
How do I know if Plan B worked? You’ll know if your emergency contraception worked when you get your next period, which could come within a week of when you expect. Your period may be heavier, lighter, earlier, or later than usual. EC pills can also cause some irregular bleeding or spotting afterward.
What are the chances of Plan B failing?
If you take it within 24 hours of unprotected sex, it is 95% effective. If you take it between 48 and 72 hours of unprotected sex, the efficacy rate is 61%. Note that if Plan B® is used on more than one occasion, the cumulative pregnancy rate will be higher.
Has anyone gotten pregnant after using Plan B?
An estimated 0.6 to 2.6% of women who take the morning-after pill after unprotected sex will still get pregnant.