Once several years ago I was prescribed an antibiotic to treat an ear infection. I was also taking the hormonal birth control pill, and ’d heard rumblings of antibiotics making the pill less effective, so I asked the doctor at the walk in clinic I was at why that was. The doctor literally said, “Oh yeah, that’s what they say. I’m not sure. Use a second method of birth control just in case.” First of all, who is “they”? Isn’t the medical professional working with me the “they” she was talking about?! Clearly I wasn’t going to get the answers I was looking for, so I’ve taken it upon myself to do a little research.
Antibiotics work by killing bacteria in your body. This means that when you take antibiotics, some of the good bacteria in your body could also be killed. This includes good bacteria in your gut or in your vagina. That’s why digestive issues and yeast infections are more likely when you’re taking antibiotics.
Birth Control Pills and Antibiotics
Turns out, there is only one antibiotic that has been proven to decrease the effectiveness of hormonal birth control and that is rifampin. Rifampin is an antibiotic commonly used to treat tuberculosis. More common antibiotics such as penicillins do not decrease the effectiveness of the pill.
The hormonal birth control pill works by giving your body doses of the hormones estrogen and progesterone. These hormones work to stop ovulation and thicken the cervical mucus, thus preventing implantation and preventing pregnancy. Rifampin can mess with the levels of these hormones, and even causes irregular periods as a side effect if you’re not on the pill. Because rifampin messes with hormone levels, that means this drug makes other forms of hormonal birth control, a.k.a the vaginal ring, patch, or shot, less effective as well. Although you won’t likely be prescribed this antibiotic unless you’re being treated for tuberculosis, it’s still important to tell your doctor or whoever is prescribing your medicine that you’re on the pill or hormonal birth control.
It is possible for other antibiotics to decrease the effectiveness of the pill if it causes you to vomit up your pill within two hours of taking it. For some peace of mind, it might be a good idea to use a secondary form of birth control, such as condoms, for the time you’re on antibiotics.
Although only rifampin decreases the effectiveness of the pill when it comes to antibiotics, other medications can mess with how well the pill or hormonal birth control is working. Some anti-HIV medications, some anti-seizure medications, and some oral antifungal medications can decrease how well hormonal birth control works. That’s why it’s ultra important to tell your doctor or whoever is prescribing you medicine that you’re on the pill. You can also explicitly ask if it will affect your birth control so you get a clear answer no matter the prescription you’re given. Antibiotics and other medications aside, the birth control pill will be most effective if you take it at the same time every day. Missing even just one day can decrease its effectiveness and lead to unwanted pregnancy.