How fast a person comes out of a coma depends on what caused it and the severity of the damage to the brain. If the cause was a metabolic problem such as diabetes, and doctors treat it with medication, he can come out of the coma relatively quickly. Many patients who overdose on drugs or alcohol also can recover once the substance clears their system. A massive brain injury or brain tumor can be more difficult to treat, and can lead to a much longer or irreversible coma.
Most comas don't last more than two to 4 weeks. Recovery is usually gradual, with patients becoming more and more aware over time. They may be awake and alert for only a few minutes the first day, but gradually stay awake for longer and longer periods. Research shows that a comatose patient's outcome relates very closely to his or her Glasgow Coma Scale score. The majority of people (87 percent) who score a three or a four on the scale within the first 24 hours of going into a coma are likely to either die or remain in a vegetative state. On the other end of the scale, about 87 percent of those who score between 11 and 15 are likely to make a good recovery [ref].
Some people come out of a coma without any mental or physical disability, but most require at least some type of therapy to regain mental and physical skills. They may need to relearn how to speak, walk, and even eat. Others are never able to recover completely. They may regain some functions (such as breathing and digestion) and transition into a vegetative state, but will never respond to stimuli.