If Aunt Flo is nowhere to be found after a round of antibiotics, your meds might start looking awfully suspect. But in reality there are many things that can cause a late period.

Here’s what to know about antibiotics and your period.

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There’s no concrete research that links taking antibiotics to a delayed period. So just because you took a Z-Pak, doesn’t mean your period is going to ghost you.

But limited research does show taking antibiotics for a long time can eff with gut bacteria. And, this *might* play a role in hormone regulation related to your cycle. (Key word: might).

Maybe you just took Amoxicillin for bronchitis or another antibiotic for an uninvited UTI. Your body’s response to the infection itself could be to blame.

Whether it’s a cold, flu, UTI, or another infection, illness and stress can eff with your period. This could include:

  • periods popping up early or late
  • shorter periods
  • heavy bleeding
  • light bleeding

Being on birth control doesn’t cause antibiotics to delay your period, but certain antibiotics can mess with your birth control.

While some docs are suspicious about any antibiotics, the only antibiotic proven to disrupt your birth control is rifampin. Rifampin increases enzymes in your body that break down estrogen faster than normal, which can make your birth control less effective.

If you’re taking rifampin, the National Health Service recommends using additional contraceptives like condoms to prevent pregnancy. The following BC methods can interact with the antibiotic:

  • combined pill
  • progesterone-only pill (aka the minipill)
  • implant
  • patch
  • vaginal ring

If you’re prescribed rifampin for more than 2 months, you may want to switch to a different BC that’s not affected, like an IUD or the progestogen-only injection.

A few medications and treatments that could be causing your period to go bye-bye include:

  • certain birth control pills, injectable contraceptives, and hormonal intrauterine devices (IUDs)
  • some anti-seizure meds and blood pressure medications
  • chemotherapy and radiation treatments (especially for hematologic, breast, or gynecologic cancer since it can destroy estrogen-producing cells and eggs in the ovaries)

If you’re taking any of these medications and you’re seeing a change in your menstrual cycle, always talk with your doc. Your healthcare professional may decide to switch medications or change the dosage to get your period back on track.

It can be hard to pinpoint exactly why your period isn’t arriving on time. If you’re noticing constant missed or delayed periods, it’s always best to meet up with your doctor to ensure nothing serious is going on.

Other reasons your cycle might be on the fritz include:

  • Pregnancy. Although a missed period can surely indicate a bun in the oven, it’s not always the case. Taking an at-home pregnancy test is a good place to start in order to confirm or deny.
  • Birth control. If you’ve recently made a birth control swap or maybe missed a few doses of the pill, your BC can be the culprit behind a missed period.
  • Body weight. Missing a period is not uncommon if you weigh less than your recommended weight for height. A 2015 study found that low weight is linked with ovulation dysfunctions and being underweight can result in irregular periods.
  • High intensity exercise. If you’ve been hitting the gym extra hard or training for a marathon your period may peace out.
  • Polycystic ovary syndrome (PCOS) or other hormonal imbalances. PCOS can raise some hormones like androgen and insulin. This can result in missed or late periods. Thyroid conditions can also mess with hormones resulting in a delayed period.
  • Other chronic conditions. Crohn’s disease, cystic fibrosis, lupus, diabetes, and celiac disease may contribute to your late period.
  • Menopause or early menopause. Menopause is a natural part of the aging process that causes estrogen levels to decline resulting in less frequent periods. Menopause typically occurs between the ages of 45 and 55, but 1 in 100 women may experience early menopause before the age of 40.

Getting your period back on schedule all depends on what made it go MIA in the first place.

Some basic basic steps you can take to keep things regular include:

  • Destress by practicing relaxation techniques like meditation or deep breathing.
  • Maintain a healthy weight.
  • If you’re a heavy exerciser, take things down a notch and opt for more moderate exercise.

In the end, if your period constantly shows up late, it’s important to have a conversation with your doctor to address the issue and set up a treatment plan.

Your antibiotic isn’t likely causing your period to disappear, but it may be affecting other parts of your body that influence your menstrual cycle. Things like your gut microbiome, being sick, and even stress may create issues with hormones that impact your period.

If your period continues to be abnormal, it’s important to set up an appointment with your OB/GYN to figure out what’s going on.