Several types of medications can make birth control pills less effective, ranging from common supplements to seizure drugs and newer weight loss medications. The interactions mostly work the same way: the interfering drug speeds up how quickly your liver breaks down the hormones in your pill, leaving lower levels in your bloodstream. In some cases, the interaction is strong enough to essentially cancel out your contraceptive protection.
Seizure Medications
Anti-seizure drugs are among the most well-documented offenders. Several of them ramp up enzyme activity in the liver, causing your body to chew through contraceptive hormones much faster than normal. The specific medications known to reduce birth control pill effectiveness include carbamazepine, eslicarbazepine, oxcarbazepine, phenobarbital, phenytoin, primidone, perampanel, and topiramate. Women taking any of these may experience breakthrough bleeding or, more seriously, unintended pregnancy.
Not all seizure medications cause this problem. Newer options like lamotrigine and levetiracetam don’t have the same enzyme-revving effect. If you take medication for epilepsy and rely on birth control pills, your prescribing doctor can often choose a seizure drug that won’t interfere, or recommend a non-oral contraceptive like a copper IUD that bypasses the liver entirely.
Rifampin and Rifabutin (TB Antibiotics)
Rifampin, used primarily to treat tuberculosis, is the single strongest known disruptor of birth control pills. In clinical studies, rifampin reduced blood levels of estrogen by 42 to 66% and progestin by 30 to 83%. At those levels, the pill simply cannot do its job reliably. Rifabutin, a related antibiotic, has a milder but still meaningful effect, reducing estrogen exposure by about 35% and progestin by 13 to 46%.
This is worth highlighting because many people believe that all antibiotics interfere with birth control. They don’t. Rifampin and rifabutin are the exceptions, not the rule. Common antibiotics like amoxicillin, azithromycin, and doxycycline have not been shown to reduce contraceptive hormone levels in any clinically meaningful way. The myth likely persists because of early case reports and overly cautious labeling, but the evidence is clear: standard antibiotics are not a concern.
St. John’s Wort
St. John’s Wort, a popular herbal supplement for mood support, is classified by the FDA as a strong inducer of the same liver enzyme system that breaks down birth control hormones. This puts it in the same category as rifampin in terms of how it interferes, though the degree varies by person and dose.
The clinical evidence is consistent. In one study, 56% of women taking St. John’s Wort alongside their pill reported breakthrough bleeding, compared to 31% on the pill alone. Another found that 15 out of 17 women experienced bleeding between periods when combining the two. Case reports have also linked the supplement to unintended pregnancies in women using oral contraceptives. Because St. John’s Wort is sold over the counter and often not mentioned during medical visits, this interaction catches many people off guard.
GLP-1 Weight Loss Medications
Newer weight loss and diabetes drugs like tirzepatide (Mounjaro), semaglutide (Ozempic, Wegovy), and exenatide (Bydureon) work partly by slowing down how quickly your stomach empties. That delay can reduce how well your body absorbs an oral birth control pill.
Tirzepatide has the clearest data: a study found roughly a 20% decrease in overall contraceptive exposure after a single dose. The manufacturer recommends using barrier contraception (like condoms) for four weeks after starting the medication or increasing the dose, or switching to a non-oral method altogether. Exenatide delayed peak absorption of pill hormones by three to four hours in clinical trials, and its labeling advises taking birth control at least one hour before the injection. Lixisenatide (Adlyxin) showed similar delays but no significant effect when the pill was taken at least one hour before or 11 hours after the injection.
If you’re starting a GLP-1 medication and use birth control pills, the simplest approach is to use backup contraception during the initial weeks and dose changes, or to discuss switching to a patch, ring, IUD, or implant that doesn’t depend on stomach absorption.
Certain HIV Medications
Some antiretroviral drugs used to treat HIV reduce birth control hormone levels by more than 30%, which is the threshold where contraceptive effectiveness may be compromised. The interaction is most pronounced with protease inhibitors that are boosted with ritonavir, including combinations of darunavir/ritonavir, fosamprenavir/ritonavir, lopinavir/ritonavir, and tipranavir/ritonavir. Nelfinavir also lowers estrogen levels significantly.
On the other hand, several HIV drugs show no meaningful interaction with birth control pills. These include tenofovir, etravirine, nevirapine, indinavir, and saquinavir. The nucleoside reverse transcriptase inhibitor class as a whole has no reported clinically significant interactions with contraceptive hormones. Because HIV treatment regimens are complex and individualized, the best approach is choosing a contraceptive method that doesn’t rely on hormone metabolism, such as a copper IUD, or confirming with your care team that your specific combination is safe.
The Antifungal Griseofulvin
Griseofulvin, an oral antifungal used for persistent fungal infections of the skin, hair, and nails, speeds up the liver’s breakdown of contraceptive hormones through the same enzyme pathway as many of the drugs listed above. Because treatment courses for fungal infections can last weeks or months, the window of reduced protection can be significant. The standard recommendation is to use a backup method of birth control during the entire course of griseofulvin and for one month afterward.
Other common antifungal medications, including fluconazole (the single-dose pill often prescribed for yeast infections), do not have this interaction.
Sugammadex: A Surgical Surprise
One medication most people have never heard of can temporarily interfere with their birth control: sugammadex, a drug used during surgery to reverse the effects of muscle relaxants. It lowers the effectiveness of hormonal birth control for up to seven days after administration. If you have a procedure where sugammadex is used, you need backup contraception (condoms, a diaphragm, or abstinence) for at least seven days following surgery while continuing to take your pill on its normal schedule.
This interaction is easy to miss because you may be under anesthesia when sugammadex is given and never think to ask about it. If you use hormonal birth control and have an upcoming surgery that involves general anesthesia, it’s worth asking your surgical team whether sugammadex will be used.
How to Tell if Something Is Interfering
Breakthrough bleeding, meaning spotting or bleeding between periods when you’ve otherwise been taking your pill consistently, is often the first sign that something is reducing your hormone levels. It doesn’t always mean you’re at risk for pregnancy, but it’s a reliable signal that absorption or metabolism of your pill has changed. If you start a new medication or supplement and notice unexpected bleeding, that’s worth investigating.
For any medication that interacts with birth control pills, the practical options are the same: use a barrier method during the overlap and for a period afterward, or switch to a contraceptive that isn’t affected. Copper IUDs have no hormonal component and are completely unaffected by drug interactions. Hormonal IUDs and implants deliver hormones locally or at steady levels that are less vulnerable to liver enzyme changes, making them strong alternatives for anyone on long-term interacting medications.