Being sick enough to require antibiotics is bad enough, but then just as you’re feeling better there’s more bad news: antibiotics mess with your birth control. Using an “alternate method of birth control” while you’re on antibiotics generally means abstinence, oral sex, or condoms. Abstinence for 10 days is lame. Oral sex is awesome, but can leave you longing for more after a few days. And condoms are… well… sigh.
Lots of people use condoms all the time, and maybe they’re used to it. If you’re slutting around with tons of people it makes sense to use condoms. But as a married couple condoms just feel wrong — not morally of course, but physically. It’s almost like you’re not even having sex. As I wrote in Yes, You Should Swallow the sharing of bodily fluids is incredibly intimate, and the condom is there to prevent exactly that. It’s like wearing rubber gloves to hold hands!
But is the worry about accidental pregnancy while on antibiotics overblown? Basically, there’s little evidence that any antibiotics other than rifampicin can reduce the effectiveness of birth control pills. Rifampicin is generally prescribed for bacterial infections like tuberculosis and leprosy, so it isn’t very common. Nevertheless, the “better safe than sorry” mentality makes everyone paranoid.
A complex study published in May, 2011 involved about 18,000 women and 1330 episodes of contraceptive failure. Researchers looked at the data on women both during months of contraceptive success (i.e., not getting pregnant) versus contraceptive failure to see if taking antibiotics made any difference. The bottom line: contraceptive failures did occur, but it was no more likely to occur if a woman was taking oral antibiotics.
Now, it’s impossible with science to prove a negative. Even the best, largest studies can’t say with 100% certainty that a super-rare event can’t occur. It could be that in very rare cases, antibiotics could somehow affect the way oral contraceptives work. So if you want to be super-safe, using two contraceptives is never a mistake. But as far as could be determined by this large epidemiologic study, women on contraceptives (excluding rifampin) were no more likely to experience a contraceptive failure than women not taking antibiotics.
If you was to be “extra safe” go ahead and use an alternate method of birth control, but is isn’t necessary. As long as you take your birth control pills every single day as directed and avoid known drug interactions you almost certainly won’t get pregnant due to antibiotics.