He should ask for a prescription for magic mouthwash (a mix including lidocaine) to numb the mouth. I also used viscous lidocaine.

On pain meds there are a variety of options. Many are put on a fentanyl patch. Others take oxycontin or oxycodone. Id make sure he tells his doctor he is in pain asap so he can get it managed. My doc was able to write me prescriptiona same day when I needed more relief.

The next weeks won't be fun but with proper prescriptions it is doable and he will make it through treatment.