Licorice for Canker Sores: What Patch and Gargle Trials Show

For a canker-sore patch, two questions matter: does covering the ulcer help, and does adding licorice improve the result? A study comparing a medicated patch with no treatment answers those questions less clearly than one using the same patch without the herb.

The trials also tested different extracts, patches and rinses. Their findings cannot be transferred automatically to licorice candy, tea or a supplement capsule.

One patch trial included an active comparison

The 2008 study¹ randomized 23 people to a licorice-root patch and 23 to a comparison patch flavored with star anise. A further 23 people were subsequently recruited for a no-treatment group. That third group was not part of the same randomized allocation. Participants had a newly developed ulcer assessed by an oral-medicine specialist.¹

By day four, 81% of the licorice group reported no pain before stimulation, compared with 63% using the comparison patch and 40% receiving no treatment. This is a particular pain measure, not an 81% complete-healing rate.¹

The protocol involved patches for 16 hours daily, excluding sleep, with patches removed before assessments. That is a study regimen, rather than directions for any current product. The star-anise comparison also means the trial did not compare licorice with a chemically empty covering.¹

A smaller study showed why the covering matters

A 2009 Iranian study² followed 15 adults through three consecutive ulcer episodes: no patch, a patch without licorice and a patch containing 1% licorice. The methods describe that sequence rather than randomized treatment order. Each patch-treatment episode involved five days of use.²

Symptoms improved with covering, and the authors described the licorice and nonmedicated patches as almost equally effective. Mean healing times were 8.46 days with licorice, 8.60 with the vehicle patch and 9.53 without treatment; the overall healing-time comparison was not significant, P=.180.²

Its small sample and successive episodes limit certainty. The result does not prove that licorice adds nothing, but it prevents assigning every benefit of a patch to the extract inside it.

A gargle trial measured short-term pain

The 2022 Taiwanese trial³ reported results for 30 licorice-gargle users and 24 placebo users. Participants rinsed four times daily; the comparator contained xylitol. On a 0-to-10 pain scale, day-two mean scores were 1.07 versus 4.08, favoring licorice, P<.001.³

The report also describes placebo participants leaving because symptoms did not improve, and its participant counts are inconsistent across the recruitment narrative. That makes the handling of missing participants difficult to follow. The result should be read with that limitation.³

Only two days of symptom measurements do not establish sustained healing, recurrence prevention or long-term safety. A gargle result also cannot identify the benefit of a dissolving patch. The paper’s root preparation is not a recommendation to brew a rinse at home.³

The recent review combines several kinds of treatment

A 2025 review included seven studies using patches, pastes, mouthwash and mucoadhesive tablets. It reported favorable findings but called for standardized formulations and investigation of long-term efficacy and safety.⁴

Those preparations cannot supply a single interchangeable dose. Some comparisons used an untreated episode, others a vehicle or another treatment. Even the review’s table identifies the 15-person study as a consecutive-group trial. Its inclusion under a review title referring to randomized trials does not change that original design.²⁴

For a product claim, check the preparation and comparator, then the outcome. Less pain on one day, a smaller ulcer and prevention of the next episode require different evidence.

Safety depends on what is in the product

NCCIH’s⁵ April 2025 guidance says the evidence remains insufficient to clearly support licorice for any health condition. It notes possible canker-sore benefits while warning that glycyrrhizin can cause serious adverse effects, including abnormal heart rhythms, particularly with substantial or prolonged consumption. Even small amounts have been linked to severe effects in people with hypertension or heart or kidney conditions.⁵

It also reports interactions with corticosteroids, pregnancy concerns with substantial oral consumption and insufficient breastfeeding safety information. Products labeled deglycyrrhizinated licorice, or DGL, have had glycyrrhizin removed; that does not make them identical to the trial preparations.⁵

Take the actual label to a pharmacist or dentist, including the extract, other active ingredients and directions. Mention medicines and any licorice teas or supplements you already use. Short trials without serious reported harms cannot establish unrestricted use.

Keep the ulcer’s history in the care decision

UK NHS⁶ guidance advises seeing a dentist or GP for an ulcer lasting more than three weeks, one that differs from your usual ulcers, or one that bleeds or becomes increasingly painful and red. Ulcers elsewhere on the body or painful, swollen joints also warrant assessment.⁶

For an ordinary short-lived ulcer, the guidance includes softer foods, a soft toothbrush and avoiding spicy, salty, acidic or rough foods. A pharmacist can discuss pain relief and other mouth-ulcer treatments.⁶

Write down when the sore appeared, where it is, whether similar sores recur and what you applied. Chapter 8, “Stones, Throats and Tongues,” in Is It My Breath? uses the Breath Log to date persistent mouth changes and organize a dental visit. A treatment that reduces discomfort should not obscure how long the lesion has been present.