I couldn't sleep last night and I took a dose of promethazine (legally prescribed). To speed it up, i took it under the tongue. Worked very fast and I fell asleep before it all melted. I woke up in the middle of the night with burning of mucosa under the tongue. It was hard and white. Couldn't sleep rest of the night. Day later it's not as bad but still sore.
Once I took something else under tongue that gave me an unpleseant reaction, but not as bad as this. Are you aware of other things that are bad under tongue?
