If you take cephalexin while using birth control, you may wonder whether the antibiotic can make your contraception less effective. This is especially common if you take birth control pills and have been prescribed cephalexin for a urinary tract infection, skin infection, or another bacterial infection.
Get SOCIAL with us!
So, does cephalexin stop birth control? No, cephalexin does not normally make hormonal birth control ineffective. It's a cephalosporin antibiotic, and current guidance does not identify cephalexin as an antibiotic that reduces the effectiveness of birth control.
The important exception is if cephalexin causes vomiting or significant diarrhea. Those symptoms can interfere with the absorption of birth control pills, which may temporarily reduce pregnancy protection depending on how long the symptoms last and which pill you use.
If you are worried about pregnancy after taking cephalexin, understanding the difference between an antibiotic interaction and an absorption problem can help you decide what to do next.
No, cephalexin does not normally stop birth control from working.
Cephalexin, also known by the brand name Keflex, is a cephalosporin antibiotic used to treat bacterial infections, including some urinary tract infections, respiratory infections, and skin infections. It does not work by changing the hormone levels responsible for preventing ovulation or otherwise disrupting the usual contraceptive mechanism.
According to the NHS, cefalexin does not stop any type of contraception from working, including the combined pill and emergency contraception. The CDC's U.S. Medical Eligibility Criteria for Contraceptive Use similarly classifies broad-spectrum antibiotics, the category cephalexin falls into, as having no restriction for use alongside combined hormonal contraceptives, unlike rifampin and rifabutin, which are flagged separately.
This means that if you are taking your birth control correctly, you generally do not need to stop it or automatically use backup contraception simply because you have started cephalexin.
For a broader overview of contraceptive options, effectiveness, and side effects, see Her Smart Choice's guide to birth control methods, types, effectiveness, safety, and side effects.
Yes, cephalexin and birth control pills can generally be taken together.
There is no established interaction that causes cephalexin to deactivate the hormones in birth control pills. This applies to common hormonal contraceptive methods, including combined birth control pills, progestin-only pills, birth control patches, vaginal rings, hormonal implants, hormonal IUDs, and birth control injections.
The concern with oral contraception is different if you become sick after taking your pill. Vomiting or prolonged diarrhea can affect how much medication your body absorbs. The CDC recommends specific steps depending on the type of birth control pill and how long vomiting or diarrhea continues.
If you want to understand how birth control pills prevent pregnancy, read birth control pills: how they work, types, benefits, and risks.
The concern is understandable because some antibiotics can interfere with hormonal contraception. The important distinction is that not every antibiotic has this effect.
The antibiotics most clearly associated with reduced effectiveness of some hormonal contraceptives are rifampin and rifabutin, which belong to the rifamycin class. These medications can increase the activity of liver enzymes that break down contraceptive hormones, potentially lowering hormone exposure.
Cephalexin is not a rifamycin. It belongs to the cephalosporin family, which is why you should not assume that taking any antibiotic means your birth control has stopped working.
Clinical reviews of rifamycin interactions have consistently found meaningful effects with rifampin and, to a lesser extent, rifabutin, while broader reviews of other antibiotic classes have not found the same pattern. This is a different body of evidence than what applies to cephalexin.
This is one of the most important points to understand.
Cephalexin itself does not normally make birth control ineffective, but diarrhea can interfere with oral contraceptive protection.
Diarrhea is a known side effect of cephalexin. The NHS advises that if cefalexin causes severe diarrhea for more than 24 hours, contraceptive pills may not provide reliable protection, and recommends checking the pill packet for what to do next.
The CDC also addresses vomiting and diarrhea among people using combined oral contraceptives and progestin-only pills. Recommendations can differ depending on the pill formulation and how long the symptoms continue.
If you have ongoing diarrhea while taking birth control pills:
Do not automatically assume that you need emergency contraception simply because you took cephalexin. The circumstances surrounding missed pills, vomiting, diarrhea, and unprotected sex matter.
Vomiting can be more important than the antibiotic itself.
If you vomit shortly after taking an oral contraceptive, your body may not have absorbed the full dose. The appropriate action depends on the type of pill and how soon you vomited.
The CDC's 2024 contraceptive guidance explains that vomiting or diarrhea can require additional steps for combined pills and progestin-only pills. If you are unsure what to do after vomiting or diarrhea, check the instructions that came with your specific contraceptive or speak with a healthcare professional or pharmacist.
You can also read what happens if you take two birth control pills in one day to understand how missed or replacement doses may be handled.
The concern about absorption mainly applies to oral contraceptive pills.
Methods that do not rely on the digestive system to deliver contraceptive hormones are not affected by diarrhea in the same way. These include the birth control implant, hormonal IUD, copper IUD, birth control shot, vaginal ring, and birth control patch.
For example, the contraceptive implant delivers hormones through the body rather than requiring a pill to be absorbed through the digestive tract. Similarly, the patch and vaginal ring don't depend on your stomach or intestines to absorb the contraceptive dose.
Learn more about how to use the birth control ring or the birth control implant guide.
A late period while taking cephalexin does not automatically mean that your birth control failed.
Your menstrual cycle can change for many reasons, including hormonal contraception, stress, illness, changes in routine, and pregnancy. Cephalexin itself is not generally considered a direct cause of contraceptive failure or a late period. However, if you have had missed pills, vomiting, prolonged diarrhea, or unprotected sex, pregnancy may still be possible.
If your period is late and you are concerned about pregnancy, taking a pregnancy test at the appropriate time can provide a more useful answer than trying to determine whether cephalexin caused the delay.
Her Smart Choice has additional information about what to do when your period is 4 days late and when to worry after missing a period.
If you had unprotected sex while taking cephalexin, the antibiotic alone does not mean your birth control failed.
Instead, consider whether any of the following happened: you missed one or more birth control pills, you started a new pack late, you vomited soon after taking a pill, you experienced prolonged or severe diarrhea, you used a medication known to interact with hormonal contraception, your contraceptive method was not used according to its instructions, or your contraceptive method was already overdue for replacement or reinjection.
If none of these occurred and you were using your contraception correctly, taking cephalexin alone is not generally a reason to assume that you are pregnant.
If you believe your contraceptive protection may have been compromised, emergency contraception may be an option depending on how long ago the unprotected sex occurred. The CDC recognizes both emergency contraceptive pills and the copper IUD as emergency contraception options in the United States.
You can learn more about when to take Plan B and how much emergency contraception costs.
If you are concerned that your birth control may have failed, a pregnancy test can help determine whether pregnancy is possible.
Testing too early can produce a negative result even when pregnancy has occurred. If your period is late or you had sex during a time when contraception may not have been effective, follow the instructions for the pregnancy test you are using and consider testing again if your period does not arrive.
For more guidance, see how soon after unprotected sex you can reliably take a pregnancy test and pregnancy tests at two weeks: when to test.
If a pregnancy test is positive and you are considering your options, you can contact Her Smart Choice to discuss confidential reproductive healthcare and available services.
There is no evidence that cephalexin reduces fertility in women or men. The NHS states that there is no evidence cefalexin affects fertility.
Taking cephalexin for an infection should therefore not be viewed as something that permanently affects your ability to become pregnant later.
If you are taking cephalexin because of a UTI, remember that treating the infection is important. Cephalexin is used for certain bacterial infections, including some UTIs, and you should take the medication exactly as prescribed.
For more information about UTIs, see Her Smart Choice's UTI symptoms, causes, treatment, and prevention guide.
If you discover that you are pregnant while taking cephalexin, do not panic or stop the medication without speaking with your healthcare professional.
The NHS states that cefalexin can be taken during pregnancy and that there is no evidence it causes harm to the baby. Treating an infection during pregnancy can also be important because an untreated infection may make you unwell.
Your healthcare professional can determine whether you should continue cephalexin based on your specific infection, pregnancy, allergies, medical history, and other medications.
If you are worried about an unintended pregnancy after a possible contraceptive failure, you do not have to figure out your options alone.
Her Smart Choice provides reproductive healthcare information and can help eligible patients understand available services, including abortion care and contraception. Telehealth consultations can also be a convenient option when appropriate and available for your situation.
California residents can access reproductive health and family planning services through the state's healthcare system, including contraception, abortion, STI care, and related services.
If you think you may be pregnant and are considering abortion, contact Her Smart Choice to discuss your options and whether telehealth consultation is appropriate for you.
No. Cephalexin does not normally reduce the effectiveness of hormonal birth control. The main concern for people taking birth control pills is whether cephalexin causes vomiting or significant diarrhea that could interfere with absorption.
Yes. Cephalexin and birth control pills can generally be taken together. Cephalexin is not one of the antibiotics known to directly reduce hormonal contraceptive effectiveness.
Not directly. However, severe or prolonged diarrhea and vomiting can affect how well an oral contraceptive is absorbed. If this happens, follow the instructions for your particular pill and consider backup contraception if recommended.
You do not automatically need condoms as backup contraception solely because you are taking cephalexin. However, condoms can provide additional pregnancy protection and help reduce the risk of sexually transmitted infections.
Rifampin and rifabutin are the most important antibiotics to know about because they can reduce the effectiveness of some hormonal contraceptives. Cephalexin is not in this group.
Cephalexin is not known to interfere with standard pregnancy tests. If you think you may be pregnant, testing at the appropriate time is more useful than assuming the antibiotic changed the result.
Yes, pregnancy is always possible if contraception is not used correctly or another contraceptive failure occurs. But taking cephalexin by itself does not normally make hormonal birth control ineffective.
A late period does not necessarily mean that cephalexin caused a problem with your birth control. Consider whether you missed pills, had vomiting or prolonged diarrhea, used emergency contraception, or had unprotected sex. If pregnancy is possible, take a pregnancy test according to the test instructions.
Does cephalexin stop birth control? Generally, no.
Cephalexin is not considered one of the antibiotics that directly reduces the effectiveness of hormonal contraception. You can generally continue your birth control as prescribed while taking cephalexin.
The main issue to watch for is vomiting or significant diarrhea, especially when you use birth control pills. These symptoms can interfere with absorption and may require additional contraceptive precautions depending on the type of pill and how long the symptoms continue.
If you have missed pills, had unprotected sex, experienced prolonged diarrhea or vomiting, or received conflicting advice about your contraception, a healthcare professional can help you determine whether you need backup contraception, emergency contraception, or a pregnancy test.
If you are in California and need confidential reproductive healthcare guidance, Her Smart Choice can help you understand your contraception and pregnancy-related options, including whether a telehealth consultation may be appropriate for your needs.
Get SOCIAL with us!
.png)
.png)
East LA: 2226 E Cesar E Chavez Ave, Los Angeles, CA 90033, United States
Van Nuys: 7220 Woodman Ave #106, Van Nuys, CA 91405, United States
Long Beach: 1760 Termino Ave #223, Long Beach, CA 90804, United States
Huntington Park: 7024 Seville Ave Suite A, Huntington Park, CA 90255, United States
©2006 – 2026 HER SmartChoice, DBA Cathedral Medical Inc. | Sitemap | Terms & Conditions | Privacy Policy
.svg)
.svg)
