Just about every medication we take comes with side effects. Sometimes, those effects are minor annoyances, such as headaches, diarrhea, or tiredness.
Other times, severe symptoms (allergic reactions or severe vomiting) might call for a discussion with the doctor about stopping the medication or switching to a different one.
The antibiotic metronidazole (Flagyl) is one medication that can cause certain side effects.
It works against serious conditions such as bacterial vaginosis, sexually transmitted infections (STIs) like trichomoniasis, and sometimes C. difficile (a gastrointestinal infection).
But metronidazole can have its own side effects, including diarrhea, nausea, and headache.
Most bacterial and parasitic infections won’t go away on their own. It’s critical to follow your doctor’s prescription instructions.
If you don’t complete your treatment, the infection could get worse, and you’ll have a greater chance of developing antibiotic resistance.
Does metronidazole cause diarrhea and nausea?
Diarrhea is a common side effect of metronidazole, affecting around 4% of people taking the medication. Nausea is slightly more common, affecting up to 12%.
As an antibiotic, it gets rid of the bacteria in your body that’s causing an infection, but it may also target the healthy bacteria that live in your gut.
This can lead to gastrointestinal side effects such as diarrhea and nausea, alongside stomach pain. But these side effects are usually mild and relatively manageable.
You generally take metronidazole as a short-term treatment of up to 10 days (although it can be longer), so the side effects should subside when you finish your treatment.
You can take metronidazole with or without food, but taking it with food may help minimize uncomfortable stomach symptoms and settle your stomach.
Stay hydrated and stick with a bland diet while you’re on this antibiotic to avoid irritating your stomach more.
You might consider avoiding all alcohol while on metronidazole, and indeed many other antibiotics.
It can increase your side effects, including diarrhea and vomiting, and it can potentially be dangerous. The label also warns you to avoid alcohol for 3 days after finishing your treatment.
“You need to be extra careful with other alcohol-containing products, like cough and cold remedies,” said Stefanie Ferreri, PharmD, and chair of the practice advancement and clinical education division at UNC Eshelman School of Pharmacy in Chapel Hill, North Carolina.
“You can have severe nausea and vomiting if you mix the two and may have a nasty hangover afterward as well.”
Finally, you might also consider taking an over-the-counter probiotic. Probiotics can be beneficial in keeping your gut healthy, and some 2021 research suggests that taking probiotics can prevent the diarrhea that often accompanies antibiotic treatment.
Other side effects
Alongside gastrointestinal side effects like diarrhea and nausea, metronidazole can cause other side effects. Some of the most common include:
- headaches
- dizziness
- confusion
- nerve pain known as peripheral neuropathy
One common, slightly bizarre side effect is a metallic taste in your mouth. Doctors don’t know why this happens, but it isn’t harmful and it should go away on its own after you finish treatment.
But it can be unpleasant, so you might want to suck on lemon drops or mints, use mouthwash, and brush your teeth regularly while taking metronidazole. Taking the drug with food you enjoy can also prevent this side effect.
Metronidazole can lead to more serious side effects as well, including having a black box warning for its risk of leading to cancer. However, such serious side effects are very rare.
Metronidazole is generally safe and well tolerated, and research suggests that lower doses are effective while causing fewer and milder side effects than higher doses.
How to get metronidazole out of your system faster
A typical course of metronidazole depends on what it’s treating, but it typically won’t be longer than 14 days, and it’s more likely to be around 7–10 days.
It’s important to finish your course of antibiotics even if you feel better to prevent the infection from returning.
The half-life of metronidazole (that is, the amount of time it takes for half of the drug to leave your body) is 8 hours.
According to the National Institutes of Health (NIH), it takes around 4–5 half-lives for a drug to completely leave your body.
Once you’ve finished your treatment, you can try to get the drug out of your system faster by making sure you drink plenty of water. But it may be best to let the drug work and leave your system naturally.
Alternatives
A doctor will prescribe you an antibiotic based on what it’s treating. But several may be appropriate depending on the condition and your individual situation. Other common antibiotics include:
- amoxicillin (Amoxil)
- doxycycline (Adoxa)
- ceftriaxone (Rocephin)
- levofloxacin (Levaquin)
Note that side effects, particularly milder ones like diarrhea and nausea, are common to most antibiotics. But they can affect everyone differently.
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