N.H. Rev. Stat. Ann. § 329:26

The confidential relations and communications between a physician or surgeon licensed under provisions of this chapter and the patient of such physician or surgeon are placed on the same basis as those provided by law between attorney and client, and, except as otherwise provided by law, no such physician or surgeon shall be required to disclose such privileged communications. Confidential relations and communications between a patient and any person working under the supervision of a physician or surgeon that are customary and necessary for diagnosis and treatment are privileged to the same extent as though those relations or communications were with such supervising physician or surgeon. This section shall not apply to investigations and hearings conducted by the board of medicine under RSA 329, any other statutorily created health occupational licensing or certifying board conducting licensing, certifying, or disciplinary proceedings or hearings conducted pursuant to RSA 135-C:27-54 or RSA 464-A. This section shall also not apply to the release of blood or urine samples and the results of laboratory tests for drugs or blood alcohol content taken from a person for purposes of diagnosis and treatment in connection with the incident giving rise to the investigation for driving a motor vehicle while such person was under the influence of intoxicating liquors or controlled drugs. The use and disclosure of such information shall be limited to the official criminal proceedings.