Metronidazole is the most commonly prescribed treatment for bacterial vaginosis (BV) and has been the standard first-line option for decades. It’s available as an oral tablet or a vaginal gel, and both forms are effective at clearing the infection. Here’s what to expect if you’re prescribed it.
How Metronidazole Treats BV
BV develops when the balance of bacteria in the vagina shifts. Normally, beneficial bacteria keep everything in check, but in BV, harmful anaerobic bacteria (the kind that thrive without oxygen) overgrow and crowd out the good ones. This causes the hallmark symptoms: thin grayish-white discharge, a fishy odor that often gets stronger after sex, and sometimes itching or burning.
Metronidazole works by getting inside those anaerobic bacteria and generating free radicals that damage their DNA, killing them. It’s selective in a useful way: it primarily targets anaerobic organisms while largely sparing the beneficial lactobacilli that your vagina needs to maintain a healthy environment. That selectivity is a big part of why it’s been the go-to BV treatment for so long.
Oral Tablets vs. Vaginal Gel
Your provider will typically prescribe one of two forms. The oral version is a 500 mg tablet taken twice a day for seven days. The vaginal gel is a 0.75% formulation applied once daily for five days using a prefilled applicator. Both are CDC-recommended options, and clinical cure rates are comparable between the two.
The choice often comes down to personal preference and side effects. The oral tablet is simpler to take but more likely to cause systemic side effects like nausea and a metallic taste in your mouth. The vaginal gel keeps the medication localized, which means fewer whole-body side effects, but some people find the applicator messy or inconvenient. If you’ve used one form before and had trouble with it, it’s worth asking about switching to the other.
Common Side Effects
The most frequently reported side effects are gastrointestinal: nausea, stomach cramps, loss of appetite, and occasionally vomiting or diarrhea. A sharp, unpleasant metallic taste is also very common with the oral form and can linger throughout the course of treatment. These side effects are annoying but not dangerous, and they resolve once you finish the medication.
One widely repeated warning is that you should avoid alcohol while taking metronidazole. The concern is a reaction that can cause severe nausea, vomiting, flushing, and rapid heartbeat. A review in Antimicrobial Agents and Chemotherapy found that this reaction actually occurs with “uncertain frequency and with varied severity,” meaning it doesn’t happen to everyone. Still, most providers recommend avoiding alcohol during treatment and for at least 24 to 48 hours after your last dose, since the reaction can be unpleasant when it does happen.
How Well It Works
Metronidazole clears BV in the short term for most people who take it as directed. The bigger challenge is keeping it from coming back. A study published in The Journal of Infectious Diseases tracked women after a standard course of oral metronidazole and found recurrence rates that might surprise you: 23% had BV again within one month, 43% within three months, and 58% within a year.
Those numbers don’t mean the medication failed. Metronidazole does what it’s designed to do: kill the overgrown anaerobic bacteria. But BV is driven by an underlying shift in vaginal ecology, and the medication doesn’t always restore a lasting balance. Factors like having a new sexual partner, douching, or not having enough lactobacilli to recolonize after treatment all contribute to recurrence. If your BV keeps coming back, your provider may recommend a longer or repeated course of metronidazole, or explore alternative medications like clindamycin.
What to Know During Treatment
A few practical things to keep in mind while using metronidazole for BV:
- Finish the full course. Even if your symptoms clear up in a day or two, stopping early increases the chance of recurrence. The bacteria may be reduced but not fully eliminated.
- Vaginal gel and condoms don’t mix well. The gel formulation contains ingredients that can weaken latex condoms and diaphragms. If you’re using barrier contraception, check with your provider about timing.
- You don’t need to treat a male partner. BV is not considered a sexually transmitted infection in the traditional sense, and studies have not shown that treating male partners reduces recurrence.
- Expect symptom relief quickly. Most people notice the odor and discharge improving within two to three days of starting treatment, though you should still complete the entire prescription.
Metronidazole During Pregnancy
BV during pregnancy is worth treating because it’s associated with preterm birth and low birth weight. Metronidazole is considered safe for use during pregnancy, and the CDC includes it as a recommended treatment for pregnant individuals with BV. The standard oral dose (500 mg twice daily for seven days) is the same as for non-pregnant patients. If you’re pregnant and diagnosed with BV, treatment is generally recommended even if you don’t have symptoms, given the potential risks to the pregnancy.