Antibiotics such as rifampicin or rifabutin and anti-fungal drugs such as griseofulvin, can make the pill less effective.
If you are on any of these medications, make sure to use a backup contraception after finishing the course.
Other forms of medications and supplements may affect the effectiveness of birth control pills as well. These include epilepsy drugs (phenobarbital, phenytoin, and carbamazepine), anti-viral medications used to treat HIV, or St. John’s wort (an herbal remedy).