Lamictal, an anticonvulsant sometimes used for migraine prevention, can reduce the effectiveness of birth control pills. If you’re using any sort of hormonal birth control (like the patch or a vaginal ring) and are prescribed Lamictal, consider using a back up method of birth control.
Note added 12/14/05: The link to the news article on this no longer works. While searching for it, I found old information that says that Lamictal doesn’t impede hormonal birth control. I’m sticking with the article I posted on — as they say, better safe than sorry.