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Can Metronidazole (Flagyl) Cause Period

Irregular periods are the type of problem almost every woman faces at least once throughout her lifetime. The thing is that various factors can influence the fragile hormonal system that controls them. However, treatment with antibiotics does not belong on the list. At least, there is no scientific evidence on it and there is no such side effect for any antibacterial medicine that is utilized in the clinical practice. Let’s discover more details on the example of Metronidazole or Flagyl.

What is Metronidazole

Metronidazole is a well-known and effective antibiotic that is prescribed for the treatment of various bacterial and protozoa infections.

Depending on the disease, it can be used in one of the next dosage forms:

  • immediate-release tablet or capsule;
  • extended-release tablet;
  • topical cream, gel or lotion;
  • vaginal gel.

The medicine is backed by science and successfully fights various species of pathogenic microorganisms, including Trichomonas vaginalis, Gardnerella vaginalis, Giardia intestinalis, Entamoeba histolytica, Bacteroides species, Fusobacterium species, Veillonela species, Eubacterium species, Clostridium species, Peptococcus species, Peptostreptococcus species and Helicobacter pylori.

It was created in France by Rhone-Poulenc that now belongs to Sanofi and was started to be produced under the name Flagyl. Then, it was one of the first drugs from the nitroimidazoles group. In the USA, it was licensed and produced by Searle, then Pfizer.

The compound is a synthetic derivative of the natural substance azomycin, which is produced by Streptomyces microorganisms. It was considered an antiprotozoal agent and was introduced for the treatment of trichomoniasis in the middle of the XX century. After the patent expired, a large number of generics were produced and nowadays they are utilized all over the world.

Understanding Menstrual Cycles

This cycle is a natural part of women’s life. It is controlled by a set of female hormones that are produced during it in different quantities. It consists of four stages, namely menstruation or bleeding, the follicular phase, ovulation and the luteal phase.

On average, all cycle lasts from 28 to 32 days, and every woman has her own duration. Ovulation happens somewhere in the middle and this is the time of the maximum fertility, e.d. the probability of getting pregnant. Before this point, the concentration of estrogen is gradually increasing and then it starts to fall.

Thus, a woman experiences mood swings according to her hormonal levels that change throughout the cycle. This is also the result of the hormonal system work.

If the system loses the balance, the periods can be missed, the spotting can be observed in the middle, etc. Each such situation requires consultation with the specialist to find out the cause and treat it properly.

Can Flagyl Cause Late Period?

There is a myth that antibiotics, including Metronidazole, influence the menstrual cycle and its duration. However, there is no truth in it and, among various side effects for antibiotics, this one is not stated.

The thing is, that the infection that is treated with Flagyl, may influence the period badly or may cause stress that changes the hormonal levels. While the body is combating the harmful bacteria, other processes can be slowed down, including the menstrual cycle.

This is probably the reason for the existing opinion about the connection between antibiotics and the late period that happens due to their intake. Still, official science and medicine do not provide us with such data. Therefore, this information is considered as a myth and there is no need to worry about this possible consequence of the intake of antibiotics.

Common Side Effects of Metronidazole

At the same time, while treating some infection with Flagyl, the patient should be aware of the possible adverse effects of its oral dosage form, which include:

  • headaches;
  • appetite changes;
  • heartburn;
  • vomiting;
  • diarrhea or constipation;
  • cramps in the abdomen;
  • metallic taste in the mouth;
  • yeast infections;
  • vaginal discharge.

Topical forms such as lotions, gels and creams may cause burning, stinging, irritation and itching of the skin, as well as its dryness and redness. The same may be observed for the vaginal forms that also belong to the group of the topical remedies.

Factors that Could Affect Menstrual Cycles

The menstrual cycle is controlled by a set of female hormones, its duration changes or stops due to the following reasons:

  • pregnancy;
  • changes in weight (both gain and loss);
  • taking birth control pills;
  • long or acute stress;
  • excessive exercising;
  • perimenopausal or menopausal period;
  • polycystic ovary syndrome;
  • imbalance of hormones.

Other diseases and regular intake of medicines may also influence this process. Thus, a woman needs to see a doctor to determine the real cause and find out the proper treatment.

What to Do If You Experience Menstrual Irregularities

When a period is late or comes early a few days and this happens rarely, there is nothing to worry about. The environment around us is constantly changing, so some response from the body is normal.

However, the following situations must draw your attention and stimulate you to visit the doctor immediately, namely:

  • periods that stopped completely and abruptly and did not appear for 60 days, especially if you are younger than 45 years;
  • three consecutive periods were missed;
  • there is spotting in between cycles;
  • there are abrupt unexplained changes in the period;
  • there is extreme pain or discomfort during the bleeding phase.

The thing is that some of these changes may occur due to the pregnancy as well as for other reasons, including diseases and life-threatening conditions. Thus, in this case, a woman requires proper diagnostics and treatment to normalize the situation.


Altogether, now you are aware that there is no link between the intake of the antibiotics and menstrual cycle. These medicines do not make the period late or early and do not have the ability to influence the hormonal balance of the women.

Still, if certain changes occur, it is necessary to find out the real cause and treat it properly. This helps to avoid numerous health issues and stay active and strong for many years ahead.


Can metronidazole affect your period?

No, this antibiotic kills bacteria and some types of protozoa infections but does not influence the hormonal balance of women.

Can I take metronidazole tablets while on my period

Yes, there is no such contraindication as a menstrual cycle for the metronidazole intake. This medicine does not have an influence on the hormonal balance and will not do any harm in this area.

Does metronidazole have side effects?

Yes, this medicine can provoke certain side effects that mainly depend on the chosen dosage form. For instance, oral forms often cause digestive system issues, while topical forms cause various skin problems.