This is the most common way people are hospitalized against their will. A doctor who believes a person has a mental disorder, as defined in the ''Mental Health Act'', can complete a certificate to admit the person to hospital, even if the person doesn’t want to be hospitalized or treated. The doctor must believe the person needs to be hospitalized for psychiatric treatment, to prevent substantial mental or physical decline, or to protect the person or other people. The mental disorder must seriously impair the person’s ability to react appropriately to their environment or to get along with others. The person does not have to be dangerous to be admitted involuntarily.