If someone has a head injury and has been put into an induced coma, how long can that person remain in that state?

Head injury coma: Typically this treatment is used to help reduce swelling in the brain and to reduce metabolic needs of the cerebrum. Treatment is usually weaned as the brain swelling improves, typically one to two weeks. Complications of immobility such as pneumonia and infections limit long term use.

Depends on cause: Following head injury there can be seizures, brain swelling, severe agitation, broken bones, etc. Some patients are put into coma in order to allow healing of body parts, some for control of seizures, some for control of brain swelling, and some to assist nursing management. Monitoring of brain pressure and eeg may indicate the coma can be reversed, or healing of body parts may take longer.