Metronidazole vaginal gel treats bacterial vaginosis (BV), the most common vaginal infection in women of reproductive age. It is not used for yeast infections or sexually transmitted infections. The gel works by killing the overgrowth of anaerobic bacteria that cause BV’s characteristic symptoms: a thin grayish-white discharge, a strong fishy odor, and vaginal irritation.
What Bacterial Vaginosis Actually Is
A healthy vagina is home to large numbers of beneficial bacteria, primarily Lactobacillus species, that produce lactic acid and hydrogen peroxide to keep the environment slightly acidic. BV develops when these protective bacteria get displaced by a surge of anaerobic bacteria, including Gardnerella vaginalis, Prevotella, Mobiluncus, and others. This shift raises vaginal pH and creates the telltale fishy smell that often gets stronger after sex or during a period.
BV is not a sexually transmitted infection, though sexual activity can increase the risk. It can also develop after douching, after a course of antibiotics, or sometimes without any obvious trigger. Many people with BV have no symptoms at all, which is why it sometimes goes undiagnosed until a routine exam.
How the Gel Works
Metronidazole is an antimicrobial that specifically targets anaerobic bacteria, the kind that thrive without oxygen. These are exactly the organisms responsible for BV. The drug disrupts bacterial DNA, which kills the overgrowth and allows the normal Lactobacillus population to reestablish itself over time.
Because the gel is applied directly where the infection lives, very little of the medication enters your bloodstream. The systemic exposure from a single dose of the vaginal gel is roughly 2% to 4% of what you’d absorb from taking metronidazole tablets by mouth. That lower absorption is a key reason many providers and patients prefer the gel: it does the same job with fewer whole-body side effects.
How Well It Works Compared to Oral Tablets
A randomized, double-blind clinical trial comparing vaginal and oral metronidazole in 263 women with BV found the two routes were equally effective. The vaginal formulation produced a cure rate of 92.5% by day eight, compared to 89.9% for oral tablets. The difference was not statistically meaningful, confirming that the gel works just as well as the pill while keeping the medication more localized.
The gel’s main advantage is a better side effect profile. Oral metronidazole commonly causes nausea, a metallic taste, and digestive upset. The vaginal gel largely avoids those issues because so little of the drug reaches the stomach or bloodstream.
Standard Treatment Course
The CDC-recommended regimen is one full applicator of 0.75% metronidazole gel, inserted vaginally once a day for five days. A higher-concentration version (1.3%) is also available as a single-dose option for people who prefer a one-time treatment. Your provider will decide which formulation and schedule fits your situation.
The gel is typically applied at bedtime. You lie on your back with your knees bent, insert the pre-filled applicator as far as is comfortable, and slowly press the plunger to deposit the gel. Applying at night lets the medication stay in place longer while you sleep. If your prescription calls for twice-daily dosing, you’ll need to wash the applicator with warm soapy water between uses.
It helps to wear a panty liner during treatment, since some gel will naturally leak out. Avoid using tampons while you’re using the gel, as they can absorb the medication before it has time to work.
Alcohol and Other Precautions
Even though the vaginal gel delivers far less metronidazole into your system than oral tablets, the FDA labeling still warns against drinking alcohol during treatment and for at least 24 hours afterward. Metronidazole can interfere with how your body processes alcohol, potentially causing nausea, vomiting, flushing, and rapid heartbeat. This applies to beverages and also to products containing ethanol or propylene glycol.
The gel should not be used by anyone who has taken disulfiram (a medication for alcohol dependence) within the previous two weeks, as the combination can trigger severe psychiatric reactions. If you’re taking blood thinners, let your provider know, since metronidazole can increase their effect.
Side Effects to Expect
The most common side effects are mild and localized: vaginal irritation, a sensation of fullness or pressure, and sometimes a watery discharge as the gel works its way out. These typically resolve within a day or two of finishing the course.
About 10% of women develop a vaginal yeast infection after completing metronidazole treatment. This happens because the antibiotic can reduce the overall bacterial population, giving yeast an opportunity to overgrow. Symptoms of a secondary yeast infection, such as thick white discharge and itching, are different from BV symptoms and respond to standard antifungal treatment.
What the Gel Does Not Treat
Metronidazole vaginal gel is specifically formulated for bacterial vaginosis. It will not clear a yeast infection, which is caused by fungal organisms rather than bacteria. It also does not treat sexually transmitted infections like chlamydia, gonorrhea, or trichomoniasis, even though oral metronidazole tablets are sometimes prescribed for trichomoniasis. The vaginal gel formulation delivers too little systemic medication to address infections beyond the vaginal canal, and its FDA approval is limited to BV.
If you’re unsure whether your symptoms are BV or something else, getting a proper diagnosis matters. BV, yeast infections, and STIs can all cause discharge and irritation, but they require different treatments. Using the wrong one can delay relief and sometimes make the underlying problem worse.
Recurrence After Treatment
BV has a frustratingly high recurrence rate. Up to half of women who are successfully treated will experience another episode within 12 months. This isn’t a failure of the medication itself. Rather, the anaerobic bacteria can persist in biofilms that are difficult to fully eliminate, and the vaginal ecosystem sometimes struggles to reestablish a healthy Lactobacillus-dominant balance.
For recurrent BV, some providers recommend a suppressive regimen of metronidazole vaginal gel applied once or twice a week for several months after the initial treatment course. This extended schedule aims to keep bacterial levels in check while the natural vaginal flora recovers.