Surgery

Prior to anesthetic the stomach is starved of food, this results in a build up of acid. If during the actual anesthetic the cat brings up some of this acid it can burn the oesophagus causing possible damage.
Some strictures can take up to 14 days to form so any sickness post operatively should be reported to your vet as soon as possible.

Drugs including the Tetracycline group.

Also known as Doxycycline, Ronoxan and others of the same family. These are often not coated and unless washed down immediately are retained in the oesophagus causing severe inflamation and scarring. It is essential that drugs are always washed down, always ask your vet for any side effects or precautions you should take.