Reasons why an adult cat won't eat or drink for 5 days after arriving at its new home:
1. Cats get very nervous and stressed when they are in a new and unfamiliar environment. This can cause their appetite to drop significantly and they may stop eating altogether.
2. When a cat is unfamiliar with its new owner, it becomes wary of people and things around it, and may become anxious and restless, hiding in a corner and refusing to eat or drink.
3. If a cat is not eating the same food it used to like, it may stop eating and drinking. If you need to change its cat food, you should do it gradually. You can mix the two kinds together and slowly switch to the new food.
4. It might be because they are too attached to their home. Adult cats are different from kittens; they are more sensitive to changes in their environment, so they are more likely to experience anxiety and unease after moving to a new home. 
What to do if an adult cat refuses to eat or drink for 5 days after arriving at its new home:
1. Let the cat gradually adapt to the new environment.
2. Prepare easily digestible food for your cat.
3. Supplement your cat's diet with digestive enzymes.
4. Change the cat food to one that your cat prefers.
5. New owners should communicate with their cats more, stroke their heads, and help the cats trust them.
