It is their duty to warn and protect. Please look at the chart at link.
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Under ethical standards tracing back to the Roman Hippocratic Oath, doctors and mental health professionals usually must maintain the confidentiality of information disclosed to them by patients in the course of the doctor-patient relationship. With some exceptions codified in state and federal law, health professionals can be legally liable for breaching confidentiality. One exception springs from an effort to protect potential victims from a patient’s violent behavior. California courts imposed a legal duty on psychotherapists to warn third parties of patients’ threats to their safety in 1976 in Tarasoff v. The Regents of the University of California. This case triggered passage of “duty to warn” or “duty to protect” laws in almost every state as summarized in the map and, in more detail, in the chart below."
http://www.ncsl.org/research/health/mental-health-professionals-duty-to-warn.aspx