Can antibiotics delay your period?
In this article
What's the lowdown?
Antibiotics are not known to impact periods
It is more likely that the underlying illness which the antibiotics are prescribed for can affect your periods
This is due to the physical stress and the impact it has on our hypothalamus in the brain
Antibiotics can affect the balance of healthy bacteria we have in the vagina
Some antibiotics are enzyme-inducing and can interfere with the effectiveness of your hormonal contraception
Can antibiotics delay your period?
I’ve got an infection, will the antibiotics I’m taking affect my period? Well, let’s not beat around the bush. No, antibiotics do not have any bearing on your periods. But the reason you are taking antibiotics might affect your periods.
Antibiotics are medications prescribed by a healthcare professional to tackle a bacterial infection you might have brewing in your body. This might be a simple urinary tract infection (UTI) or a more complicated sexually transmitted infection (STI).
Please do not take antibiotics without seeking a doctor’s opinion or stop antibiotics before you finish the course as this can lead to antibiotic resistance and the spread of infections1.
It is usually the ‘stress’ of the illness on your body which can delay or prolong your period. We don’t mean mental stress in this case. When you’re unwell, your body uses up a lot of energy to fight the illness. This puts extra pressure on the brain’s stress-response system, known as the hypothalamic-pituitary axis (HPA axis)2. This causes an increased production of cortisol (stress hormone) which interferes with the regulation of other hormones (like the ones required for our menstrual cycle)3. This interaction can potentially lead to abnormal ovulation or anovulation (no ovulation). Without ovulation, there will be no egg released. This disrupts the cascade of hormones that trigger the stages of the menstrual cycle and can cause a delay in the shedding of the uterus lining in the form of a period4.
Do antibiotics affect your vaginal flora?
It’s well known that antibiotics can disrupt your vaginal flora. Like your gut, the vagina has a delicate balance of healthy bacteria known as the microbiome. The dominant group of bacteria in the vaginal microbiome is Lactobacillus5, which plays a key role in maintaining a healthy environment. However, antibiotics don’t just target harmful bacteria, they can also reduce levels of beneficial bacteria like Lactobacillus. This disruption can alter the composition and diversity of the vaginal microbiome, increasing the risk of developing conditions such as a UTI or thrush6.
Can penicillin affect periods?
Penicillin was the first antibiotic discovered in 1928 by Alexander Flemming in St Mary’s Hospital in London7. As an antibiotic, it has a wide range of uses and is commonly prescribed in medical practice but has no effect on periods.
Can amoxicillin delay your period?
Amoxicillin is an antibiotic of the penicillin class, commonly used to treat chest infections and dental abscesses8. It is not known to interfere with periods.
Can antibiotics affect contraception?
Certain antibiotics can speed up the way your liver breaks down the hormones in the contraceptive pill, a process known as metabolism. This can lower hormone levels in the body and reduce the pill’s effectiveness. These types of antibiotics are called enzyme-inducing antibiotics, and include examples like rifampicin and rifabutin.
However, the good news is that most commonly prescribed antibiotics are not enzyme-inducing, so they won’t affect your contraception. That said, it’s always important to let your doctor know if you’re using hormonal contraception so they can prescribe antibiotics that won’t interfere with its effectiveness.
If there’s no alternative to an enzyme-inducing antibiotic, you may need to use a barrier method (such as condoms) while taking the antibiotic and for 28 days after finishing the course.
To learn more, check out our detailed blog on how antibiotics can interact with the contraceptive pill.
Dr Fatema Dawoodbhoy
Fatema is currently training in London as an Academic doctor, with a special interest in Obstetrics and Gynaecology. She is passionate about championing women to understand their bodies better and prioritise their health. She understands the importance of clinically accurate articles and has been writing engaging and educative medical content for 5 years.
Our medical review process
This article has been medically reviewed for factual and up to date information by a Lowdown doctor.
