Dexamethasone mouthwash is a steroid rinse you swish around your mouth and spit out. It works by direct contact with inflamed tissue, delivering anti-inflammatory and immune-suppressing effects right where they’re needed. The standard version is a solution containing 0.5 mg per 5 mL (one teaspoon), and a typical dose involves swishing that teaspoon for two to five minutes before spitting it out. Getting the technique right matters, because the longer the solution stays in contact with your tissues, the better it works.
What It Treats
Dexamethasone mouthwash is prescribed for chronic inflammatory conditions inside the mouth. The most common is oral lichen planus, a persistent immune-driven condition that causes painful white patches, redness, or open sores on the gums, inner cheeks, or tongue. It’s also used for other non-infectious oral conditions like recurring canker sores (aphthous stomatitis), mucous membrane pemphigoid, pemphigus, and erythema multiforme.
Some oncologists prescribe it to help prevent or manage mouth sores caused by chemotherapy (oral mucositis), particularly in patients receiving treatment for breast and other cancers. In these protocols, the concentration and frequency may differ from what’s used for lichen planus.
One critical point: this rinse is only for non-infectious conditions. Steroid rinses suppress local immune activity, which means using one when a bacterial or fungal infection is present can make things worse and potentially allow the infection to spread.
Step-by-Step Instructions
Your prescriber may give you slightly different directions, but the standard protocol used in clinical settings follows this pattern:
- Measure one teaspoon (5 mL) of the solution. Most pharmacies dispense it in a bottle with a measuring cup or oral syringe.
- Swish gently around your mouth for two to five minutes. Clinical protocols vary: some call for a two-minute rinse, others for a full five minutes. Try to direct the liquid toward the affected areas. Do not gargle unless your provider specifically instructs you to.
- Spit the solution out. Do not swallow it. The medication is designed to work on contact with the lining of your mouth, and swallowing it introduces unnecessary systemic steroid exposure.
- Do not eat or drink afterward. Wait at least 15 minutes, and ideally 30 to 60 minutes, before putting anything in your mouth. This gives the residual medication more contact time with the inflamed tissue. The University of Iowa’s oral medicine protocols recommend waiting 30 to 60 minutes for best results.
How Often to Use It
For oral lichen planus and similar chronic conditions, the typical frequency is three times per day. Some chemotherapy-related protocols call for four times daily. Your prescriber will set the schedule based on the severity of your condition.
A standard four-week supply is about 480 mL. Treatment courses commonly last four to eight weeks, though some conditions require longer use with periodic reassessment. Dexamethasone has a long biological half-life (36 to 54 hours), which means each dose continues suppressing inflammation well after you spit it out.
Getting the Most From Each Rinse
The single biggest factor in how well this mouthwash works is contact time. Swishing for 30 seconds and spitting won’t deliver the same benefit as a full two-to-five-minute rinse. If holding the solution in your mouth for that long feels difficult, try smaller, more deliberate movements rather than vigorous swishing. Some people find it easier to tilt their head to let the liquid pool over the affected area.
Timing your rinses around meals helps with the fasting window afterward. Using it first thing in the morning (before breakfast), mid-afternoon, and before bed gives you natural gaps where you’re not eating. If you’re on a four-times-daily schedule, adding a dose after lunch works well.
Oral Thrush and Other Side Effects
The most common side effect of any steroid mouthwash is oral candidiasis, commonly called thrush. Reviews of topical steroid use in oral conditions report thrush rates of 25% to 55%, with higher rates linked to stronger steroids, longer treatment courses, and higher concentrations. That said, topical rinses carry a much lower risk of serious side effects than oral steroid pills or injections.
Signs of thrush include white patches on your tongue or inner cheeks, a cottony feeling in your mouth, or a burning sensation. If you develop these symptoms, your provider can prescribe an antifungal rinse to use alongside or in place of the steroid temporarily. Some clinicians prescribe a preventive antifungal from the start for patients expected to be on the rinse for more than a few weeks.
Because you’re spitting the rinse out rather than swallowing it, systemic steroid side effects (weight gain, blood sugar changes, bone thinning) are uncommon with standard doses and typical treatment lengths. Swallowing the rinse regularly, however, increases that risk, which is why the spit-not-swallow instruction matters.
Storage
Dexamethasone mouthwash is often compounded by a pharmacy rather than manufactured as a commercial product, so storage matters. Compounded dexamethasone solutions remain stable for up to 91 days whether stored at room temperature (around 25°C / 77°F) or refrigerated, in either glass or plastic bottles. Stability studies show the solution retains at least 96% of its original concentration over that period.
Check the expiration date your pharmacist puts on the label. If your bottle doesn’t have one, a safe assumption is 90 days from the date it was compounded. Refrigeration isn’t required but won’t hurt. Some patients prefer the rinse slightly chilled, especially if they have sore, inflamed tissue.