Mucositis can be treated with painkillers, mouthwashes, and other treatments. Pain medication Painkillers: Tablets, gels, sprays, or mouthwashes that can help with pain Opioids: Short-acting opiates or transdermal fentanyl can help with breakthrough pain Steroids: Dexamethasone mouthwash or oral prednisolone can help with lesions and ulcers