I have been taking MTX for my RA for about a year and have had severe canker sores the whole time. I tried everything from oral numbing gel to salt water to hydrogen peroxide to prescribed "Magic Mouthwash". Absolutely nothing helped to alleviate the pain for more than maybe 30 minutes. Then, I found "Canker Covers". These things are an absolute godsend! They actually stick onto the sore to keep it protected from bacteria and irritation. And they stay on for hours! 12 bucks is sooooo worth the relief! I hope this helps someone else who has been as miserable with mouth sores as I was!