The move follows heightened public concern about the ethics of stopping the treatment of patients being kept alive artificially.
There have been a number of reports of patients in a persistent vegetative state (PVS) waking up or showing signs of consciousness.
The college said the guidelines were drawn up before the recent case of a businessman who started communicating with hospital staff after being in a PVS for seven years.
They would be reviewed again once the clinical details of the case had been studied.
The guidelines followed a recommendation from the House of Lords Select Committee on Medical Ethics that PVS should be defined and a code of practice developed.
They recommend that a diagnosis of PVS should only be made when a patient has been in a continuing vegetative state for more than 12 months after a head injury, or six months following other causes of brain damage. A continuing vegetative state was said to occur when the patient failed to show signs of recovery after more than four weeks.
Professor David London, registrar of the college, admitted that the guidelines might have to be altered in light of the latest case.
"Our guidance is based on the best evidence available to us at the time and is intended to help doctors by differentiating the clinical states in line with current knowledge," he said.
"When we have seen the clinical details of this recent case, we will review the guidance we have given."Reuse content