Thanks for the question. A common side effect of ecstasy abuse is bruxism, which is the medical term for teeth-grinding. This is caused by the massive release of serotonin in the brain caused by ecstasy. Commonly, people will grind their teeth or chew on their cheeks and lips. This is likely what happened to you, resulting in the sore you describe. Ecstasy use can be dangerous. You never know what is mixed in when you consume illegal substances, because they are not regulated. I would advise you stop using ecstasy for your own general health. If you have further questions or concerns, I would speak to a primary care doctor or psychiatrist. I hope this helps. Dr. Sheppe