How long after getting a root canal are you fully functional again?

Same or next day: Short term recovery is expected. Some people have little or no post op symptoms. Depends in part on pre op symptoms and your own immune system.

Immediately: Once the root canal therapy is completed and the tooth is properly restored your tooth is fully functional.

Depends.: Depends of condition of tooth. Inflammation around the tooth may have to resolve to feel better. This is usually relatively soon but sometimes takes longer to feel fully normal. To be "fully functional" the tooth has to be properly restored so it can bear chewing pressure without breaking, often with a crown or other covering. Don't wait too long after finishing the root canal to do this!